Hi Tomas. Great to see your low flow temperature experiments. We have recently done a similar thing with advice from a Heat Geek engineer. Before we got his help we were running our ridiculously oversized boiler with flow temperatures suited to radiators, even though we have UFH throughout. We have never really understood how to get the best from the system until we got advice from Leon. He removed a pump from the manifold and changed our zoning set up to open loop using the boiler pump and weather compensation. Our flow is set at a max 45deg, but often runs lower. This is our first winter with the new set up. We are comfortably warm and no longer turning the heating up and down. We run the system from 3 am to 9.30pm. I was nervous when we had the first snow in November but the new set up worked a treat and cheaper to run than our previous on/off set up. Look forward to move videos on your journey to a ASHP as we want to make the same transition.
I’ve been tracking our gas usage over two winters now. We have been using a flow temp of 50 degrees and as we are both at how all day, this year we have basically had the whole house at a constant temperature all day and night. Not only have we been consistently using less gas than lat year, we also haven’t had to put up with the house (especially downstairs) being cold for the first couple of hours in the morning
Apparently that is the magic number, 50c, coincident I arrived to that number too. after study the basic how the boiler do condensation and the saving tipping point value. I put my thermostat at 17.5c "
@@tomasmcguinness this discussion has prompted me to look back at the historic data in our Tado app for the heating zones, how much temperature variation there was and how much time that zone was calling for heat. It’s really quite surprising how much more effective it is to aim for a constant temperature, especially as it’s more comfortable and the system isn’t chasing a constantly changing target.
Had a similar result. Last November ran boiler @ 50 degrees between 16:00 - 21:00 each day and used an average of 23.9 kWh per day. This year tried it at 36 degrees flow and had a set back of 18 degrees over night and then 19 degrees first thing, followed by 18 degrees during the day and then 19.5 between 16:00 - 21:00. We used an average of 45.37 kWh per day, keeping the house nice and comfortable 24/7. Noticed a massive reduction in condensation.
Brilliant. Condensation is an interesting one. If the fabric of the building stays warm, there aren't as many cold surfaces for condensation to form on. Of course, if the building cools down enough, you will get condensation again. If you're getting a lot of condensation, I'd look to identify the source and maybe look at ventilation changes.
Something is odd here, last year you said 23.9 kwhr per day at 50 Deg and now you run at 36 for a longer period and use almost twice the energy at 45.3 kwhr. Is that a benefit? I can see why the condensation reduces but why do you have any condensation in the 1st place and where? But it's at almost twice the fuel cost,.......... Or have I misunderstood your savings ?
@stevew9957 OK, here goes. 2023 boiler running 5 hours on an evening. No heating on from 21:00 until 16:00 next day. House cold, trying to save money. This year tried it where heating on to maintain a minimum of 18 degrees over 24 hours, with 2 periods where it increases to 19 and 19.5 respectively. So home heated 24/7 as required. But only 22kWh for additional 19 hours of heat and comfort. Condensation is more of an issue in bungalows, ours is made worse by having a conservatory. So when you have no or little heat the air can't hold the moisture and this condenses on the glass. Hope this helps.
We have a smallish 3 bed semi detached built in 2018 but it does seem pretty well insulated. Peak gas used through days with with snow and about -2 outside including cooking and hot water is never more than 50kWh per 24hrs
Have had my gas CH on various temps 24/7 for 20 years and, with good rad & room stat controls, found this to be the most efficient way to heat a 4 bed detached house and now a 4 bed bungalow. Boiler flow temp is kept at 55 degrees on my Greenstar CDi system boiler, bedroom rad stat at 2/3 with hall & livingroom at 4/5.
Anything at 55 or under is great, since your boiler will be working more efficiently. Not a fan of TRVs myself, but if it's working for you and your comfortable, it's working for you!
Great, interesting but complex subject, some points for consideration as well, electrical consumption of the boiler is related to run time of boiler and also optimisation is affected by flow temp i.e. at the higher flow temp the start time should be later in order to reach room temperature at the start of the occupied period and the stop earlier because of greater residual heat content which you did of course acknowledge at the end.
Thanks. It's very hard to account for everything in tests like this and they aren't the most controlled environments either, but it's interested to see broad results.
Interesting stuff Tom. Very informative. Actual house with figures! Love it. If you ask 'Google' it says something like 33KWH a day average, and I think - how? I'm in a 1934 bungalow, cavities and roof insulated, running a 40 year old fanned boiler set to 50c on Y plan F&E system with a delay unit to control firing, set to 12 minutes delay at the moment. On 14 hours a day and consuming about 55KWH a day with cooking and hot water. Seems to work. Of course I then think would a new Combi save me money? Or the glories of a Heat Pump that we see folk telling us they are so cheap to run whilst dressed in their thick woolies! Keep up the great content. 😊
Thank you! Glad you found it interesting. If you average out gas usage out over the whole year, the daily number is rubbish. Average UK gas usage is 12,000kWh annually, which is your 33kWh a day. Doing that to my usage is only 43kWh a day. Upgrading from a 40-year-old boiler would see you saving money, as condensing boilers are more efficient, especially with a flow of 50c. Heat pumps do work perfectly well but need due care and consideration when being installed. They are not forgiving of poor design or installation.
hi john how far are the water runs to the kitchen and bathroom to the tank, do you leave the hot water demand on all the time or just set on a timer say twice a day.
@stephenfanthorpe2708 Hi, quite a long run from hot cylinder to the taps, as in most F&E systems but have an electric shower. In summer two times sessions for hot water but when heating is on so hot water priority is the rule, no hot water off -but - I've fitted a HW off switch to boost heating if needed. (A DPDT switch overrides tank stat)This because I've also fitted a delay unit (555 timer ic) to delay firing. It works for me, and boilers only half my age, but I guess a combi has got to go in one day!
@ I find often in bungalows in the loft as close as central to the bathroom/s kitchen is ideal if you go the combi route just for less lost time getting to temp at the taps especially if you use a lot of 2minute water. If you have currently say a baxi solo or an ideal classic boiler you’ll be looking at 25% better efficiency minimum m. If you do go combi ensure they match the hot water output to your mains water flow rate a 30kw with 12l a min flow capacity isn’t as efficient as a 24kw with 9l if you only have 6l a min flow to play with. Condensing boilers need to condense to be as efficient as the tag. Calculate the heat loss per room get the radiator capacity and your water usage that is the way to plan it properly to save money hit a delta of 40-50 and you won’t believe how cheap a boiler can be to run in comparison even the one you have now. I think maybe your rads are somewhat small or you maybe haven’t enough carcass in the pipe work to keep it efficient as it could be.
Heat pumps are good and have about the same running cost as efficient gas if reasonably installed. The benefits to me are the reduced emissions and the modern heating controls, which are good, being more sophisticated than my old gas boiler. It should also never need upgrading (will need fixing and might need replacing at some point). My solar, battery and time of use tariffs are what help bring the cost down below what I had previously (as they would had I kept my old heating system).
5 bed house, integral garage. Run our heating at 36 degrees day and night, even in the cold snap. We have 10mm microbore drops to radiator. No heating in the main bedroom. We got a good drop in bills (still on old meter) and for 4 adults inc 2 gamers our bills are £10 more per month than our neighbours in the same house config - run their heating only morning and evening and retired but also out a lot. Happy with that I do have some more tweaking to do re pump speed and other bits. Houses are predominantly sold block walls - very little studding so I work on keeping thermal mass in the house
That's great! 36 is really good and shows microbore isn't the end of the world either. I really need to find out what my street uses in terms of gas. I've been pondering a survey or some type to share as I'd be fascinated to see how my usage compares!
@@tomasmcguinness I watched an Urban Plumbing video that opened my eyes to it. Funnily enough it was done while he was putting in UFH for going to a heat pump and he showed running a low flow temp to heat his house while it was sub-zero outside . He also helped (via email) with selecting our Intergas Boiler which has so far been fantastic.
I've had a look back at some of your previous videos and found that you have a 2 storey house of about 150m2 total floor area? Can I ask if the overall structure and insulation is typical of your area? It's just that I'm utterly staggered by the energy consumption, our approx 150m2 bungalow in the north Highlands has a maximum 24hr heating consumption (space and DHW) since I started measuring it in 2017 of 33.9kWhr, that was on January 18th this year when the outside temp was -7c and the wind 50mph+. I measure all the energy going into our thermal store from the heat pump, solar thermal and solar diverter, so can't split out the DHW. We do get much colder weather, but that tends to be very still so heat loss is actually lower. I keep hearing that the UK housing stock is badly insulated, but never realised a typical family home owned by someone actively try to reduce energy consumption would be consuming over 100kWhr/day with the outside temp hovering around 0C. I find that a bit depressing really.
What?? That's crazy!! 34kWh for one day when it was -7 outside?? That means you were only putting in about 1.5kW of heat over the whole day? You're right about the house, 4-bed, detached. Heat loss is about 7.5kW for 21/-3, so to maintain 21 over a whole day would be 180kWh. My house is better insulated than most on the street. It's a 1950s, with suspended floors and cavity walls. I have insulated the floors, the loft and even had cavity wall insulation added. I know that's more than most of the houses of the road. I am going to try and survey my neighbours in Jan/Feb to get a feel for energy usage on the street and see how mine compares. Usage pattern is important to consider too. We're working from home all day, so we will have the heating on more than those who are out at work.
@@tomasmcguinness Yes, 1.5kW in those conditions is about right, the heating is at 21c 24/7, except the spare rooms where it's 18c if no visitors. Over the last 12 months to date we've put 4081kWhr of heat into the thermal store from all sources, I estimate 1400kWhr is used for DHW so about 2700kWhr for heating. Our house was built 20 years ago, it's a 140mm timber frame and suspended floors, 140mm PU in both plus 20mm over the complete wall to minimise bridging then Fermacell to finish. 40mm PU on the window and door reveals. 40mm PU under the floor for anti-bridging. 400mm Rockwool in the loft and eaves "fences" to prevent cold air being blown under the insulation. MVHR, triple glazing and I was pretty obsessive about sealing every little gap. The trades helping me thought I was mad to exceed building regs requirements, at that time oil was maybe 12p/litre, but it was as much about comfort and only added about £7k to build costs Leak tests weren't required at the time but I do them periodically using the MVHR, I can do both positive and negative pressure tests by blocking the inlet or outlets as necessary and turning the opposite fan to maximum. Typical results are 20litres/sec at 15Pa for the entire house, that equates to around 1.1 air changes per hour at 50Pa, so nearly double that allowed for Passivhaus but well above current building regs. I have a comparison with a friend's house, similar size bungalow to ours and same age but built by a developer. They're still on a condensing oil boiler and use around 1100 litres/year, it's probably around 85% efficient so that's 9600kWhr in total, assume 1400kWhr for DHW therefore 8200kWhr for heating; or 3 times our heat requirements.
One caveat with low flow temperatures - the radiators need to be big enough to dissipate the minimum modulated burner output. If the heat demand is below that the flame will cycle on and off; would welcome any data about that affects boiler efficiency (from recent YT videos it seems to have a bad effect on heat pumps). PS - My Y Plan system uses the same boiler temperature for heating and hot water. As such, the lowest I can go to get usable hot water is 55 C. Between Spring & Autumn my solar panels add extra heat to the water so I can go lower but there is precious little sunshine this time of year.
My boiler is so big, the minimum is between 5kW and 6kW. I asked the plumber to put in some oversized radiators, thought I didn't even know what that really meant at the time. The hotter the radiators, the more heat they will output, but as I show, when it's zero outside, a 40 flow temp is still enough to get the house up to 20ish. Last winter, when it was -5, a 45 flow was enough. Heat Pumps really don't like cycling. It's far more inefficient then a boiler, so good design is important to ensure the heat pump is correctly sized. If my boiler was 20kW and could modulate down to 2kW, it would *never* need to cycle. I have an S-Plan system, but was able to jury-rig support for two flow temperatures, so I can use 70 for hot water and anything else for heating. There are a few videos in my channel on how I did it.
I run mine at 52c and it's on timer, runs around 7 hours a day, 4 bed end terrace 1950's house, well insulated, using around 30kw a day of gas and then I light my wood burner at 6pm. Wood burner is essential when it's sub zero in an older house as before that I could use 140kw of gas a day in a cold snap and it would be chilly in here, now T shirt in the evening.
Good question and I have wondered this too. Electricity usage isn’t all that much. I monitor this and if my boiler was running for 24 hours solid it would use about 1kWh of electricity. Wear and tear - not sure. I have heard that restarts cause more wear than continuous operation. There is also much less thermal stress & shock since pipes, joints etc. stay at a steady temp. I don’t have any empirical evidence for this, just what I hear from professionals.
Great video and data. Could you compare a day when you go out with a heat in the morning, off all day, then heat in the afternoon/evening before you get back? It'd be good to see how much the efficiency cancels out the saving from the lower delta loss. Your indoor temp was slightly higher on the thermostat day, so I guess a lot of the extra energy was due to the delta to outside. Comparing my octopus figures on the same day, I guess your house is a lot bigger than mine 😮
Would that with the high flow temp vs the low flow temp? And you're right about the set point being high. We find that when the heating isn't on (i.e. the boiler isn't firing), we *feel* colder, so I set it at a higher value. That said, the outdoor temperature during the day was *higher* so the internal/external dT was probably less. I need to add a sensor to track the dT as that would be useful. House is a four-bed detached property with a 7ish kW peak heat loss.
@ yeah on the high vs low flow temp. The warmer temp makes sense to feel the same warmth if there isn't as much mass giving off stored heat. dT vs COP would be a good comparison when you get a heatpump. I'm in a 3 bed detached, but not much distance between the houses, and with a low flow temp it has taken a while to heat up.
Hello Tom I notice your consumption for that cold period is high do you use other gas appliances? On 19Nov (-1c) my baxi duo tec 24 combi used 81kwh. On a regular day with outside temp at 5c I use just below 60kwh per day. I live with family of 4 in a 1950's semi detached 3 bed 100m2 my flow temperature at 45c to get my house to 22c from 5am to 10pm. All Trvs but room with thermostat set at 4 throughout.
I don't think it's too high for the property. I live in a 4-bed detached house, around 150m2, so my usage at around 120 is proportional enough to your 81. Peak heat loss on my house is about 7.5kW when it's -3 outside, meaning I'd use around 140kWh on a very cold day with the heating running constantly. I have *no* TRVs in the system, since I don't believe they bring any values.
I don't know if this is covered in other videos, But this would only be condensing boilers. A condensing boiler condenses the water out of the exhaust, which extracts more heat, but if the temperature is too high, it condenses outside, losing energy. So that cloud of smoke you see coming out of boiler flues, is actually steam, and thats energy a condensing boiler should be capturing. heat pumps should also be more efficient at lower flow temperatures, but for different reasons.
I don't think there is anything stopping a *non* condensing boiler running with a low flow temperature. I know must older boilers had to run at 80 to stop corrosion and that choice of temp was carried forward to more modern boilers. This is part of the problem with most default flow temp settings today.
@@tomasmcguinness You can run any boiler at a lower flow temp. You aren't going to see any benefit. A condensing boiler uses less energy because it condenses. a lower flow temp means you will be able to condense more water out of the exhaust. None of this is relevant to a non condensing boiler.
Of course it is. Running a lower temperature will use less gas. I’m trying to show that you can run all day at a low temp and use less gas than a high temp. In both of these cases, my boiler’s efficiency is pretty much the same. It just takes less energy to heat water to 40 than 70.
@@tomasmcguinness Wheres the saving coming from? assuming youre heating your house to the same average temperature, you aren't losing less heat from the thermal envelope. and gas doesn't burn more efficiently at a lower temperature See for example ua-cam.com/video/wFOpHNz7Fdc/v-deo.html specifically around 4:12
Running longer at a lower temperature consumed less gas the high flow temp. It’s not a perfect comparison as the weather was warmer. In the video you refer to, Szymon is talking about efficiency. I’m looking at consumption. My boiler is operating in condensing mode in both of these tests, since the return temp stays below 55. If you look at the blog post, I address efficiency in its own section.
I see from your graph that your indoor temperature during your high temperature flow was a little higher than during the low temperature day. It's difficult to see exactly, but it looks like about 2 degrees warmer on average throughout the day (something like 21 vs 19). If it is that much, this would account for quite a large amount of heat input, I would suggest. Secondly, 21C is really warm. You could save messing aroung with flow temperatures by turning your thermostst down and wearing a jumper.
Well spotted! Under thermostat control, the set point was 21. It has to be higher to make the house feel as comfortable, since the boiler is stopping and starting. The outdoor temperature is also higher on that day, so the delta is about the same. Having the heating on all day means the indoor target temp is lower, yet we feel as comfortable. We do wear jumpers anyway, as that just makes sense in colder weather. If we were walking around in t-shirts and shorts, the set point would need to be even higher.
Totally agree with this I got the same result with my 15 year old baxi 33kw combi. I tried to run it at 40 but it short cycles so the lowest it is happy to run is 50 but that does the trick and keeps the house warm without excessive bills. It is also useful to know the flow temperature that I will need for when I get a heat pump.
Same here - my Baxi can only modulate down to 9kW and so anything lower than 50C the rads can’t get rid of the heat and short cycles - in principle a HP of a similar size will match my heat loss at -3C and can the compensate up to 50C as and when needed 👌
@@tomasmcguinness this our plan as well. We’ve had solar and batteries for about 18 months now and even with gas heating and an EV we are not far off being cost neutral over a full year. The only part of our house which may need some plumbing changes is the downstairs front hallway. It s north facing and the coldest part of the house. Layout means there’s only limited radiator space and although there is a good size 1800mm tall radiator, in fitting in very small pipe has been used (8mm copper) and I don’t believe that 8mm can carry enough energy at sensible flow rates to keep the hall warm. A new, very efficient front door and triple glazed side panel are going in and may solve this but otherwise we will have to have bigger pipes chased down from upstairs. Still, gives me something to do I suppose.
The question to answer is, where does the excess energy go? Because if the house had the same comfort levels on both days there must have been increased losses. My guess would be increased flu losses due to increased output. If the space temperature remained the same then the fabric losses should have remained equal for both scenarios. Any thoughts?
Good question. At this point, I believe it's all down to the ferocity of the burn. The boiler won't start modulating its power until the flow temp is at the desired level. It burns like crazy to get the water up to 70. It never does because the house's temp gets pushed up and the thermostat tells the boiler to turn off. It's related to my boiler being oversized too. I have limited my boiler to 50% of its max, so when it starts, it's putting out about 18kW before it starts to reduce its power. It burns like that 10 times in the day. With the lower temp, it has a large burn at the start, but the water reaches 40 very easily (as the water starts at 15) and once it's up to temp, the boiler throttles all the back to its lowest output. The temperature on the high temp day also fluctuates, up and down, as the thermostat tries to meet the desired temp. On the low temp day, the indoor temperature slowly rises to the desired level and then flattens and remaining constant.
@tomasmcguinness that explains a lot thanks. All of the energy must go somewhere so if the room temperature fluctates above the desired setpoint the delta between room and outside will be greater which will lead to increased fabric losses at those times. Gas burns at the same temperature regardless of the water flow setting, which is likely to equal greater flu losses when the boiler is operating, though it seems like the boiler is range rated. Either way look into the benefits of compensated heating control, which will increase radiator temperature in winter and decrease radiator temperatures in milder conditions. If you combine compensated heating with a condensing boiler you'll also reduce the boiler flu losses. Until then it looks like your heating system might be oversized, which is a good thing and allows you to operate a lower 40*C radiator temperature setting even in winter. Great experiment and I really enjoyed the video. Thank for putting this together Tomas 👍
Is this just balancing the reduced heat loss from the house being cooler while you're out, vs reduced boiler efficiency when run at full power? If your house is well insulated and has lots of thermal mass, it won't cool down much while the boiler is off, and will continue to lose heat at close to the normal rate - and low-and-slow will work well. OTOH if your house cools down to ambient when you turn the heating off, it will stop losing heat entirely and an on-off strategy would work better. I'm not really sure what affects boiler efficiency. I'd imagine there's a critical power where a condensing boiler's exhaust it above boiling point and your efficiency drops drastically. I think it would be useful to plot heat loss and boiler efficiency, and model what happens in different scenarios.
if the higher flow temp was running the boiler flat out for a period of time to get the house temperature up to the desired target than does that mean running the boiler at the lower flow rate took much longer to reach the same desire internal temperature ? in which case one would assume the net gas consumption is the same albeit allowing some small difference ?
That's what you'd assume, but it turns out not to be the case. If you look at the graphs, the morning burn at 70 degrees used almost 60kWh of gas in the first three hours. The low burn used around 20kWh in the same period of time. The boiler has to work *much* harder to heat water to 70. Perhaps my experiment was flawed, but the data showed that across the whole day, leaving the heating on used less gas.
the laws of physics tells us you use more energy to heat a house all day; heat loss wont be less bc the house is kept warm 24/7; the answer is always better insulation
On that day, the outdoor temp didn't really get above zero at all. I was running at the slightly higher flow temp of 45 too and the hourly consumption was a little over 8kWh. The startup usage was high as I think the fabric lost most heat because it was -2 for most of the night.
I tried this in my 1992 4 bed detached Mcleans house. It didnt work, for what i think are the three main reasons; 1. Some of the radiators/emitters are original whoefully undersized units piped in 10mm microbore. 2. The 2007 Baxi 40kWh boiler doesn't modulate sufficiently at 50C let alone lower temps, it cycles constantly. 3. Excessive heat loss. The third reason is why I wont go for a heat pump! Ill probably try and bag a more efficient boiler. Im surprised this test wasnt carried out with the boiler in condensing mode, ie return temp < 55°C. I think the results would have been closer.
Good on you for giving it a try! If the rads are undersized at 70 you have no hope with anything lower :) My boiler is 35kW so I feel your pain! How excessive is excessive? Have you had a heat loss survey done? My test? For the most that, the boiler was always operating in condensing mode. Even at 70, the return only passed 54 for two very short periods. That is why I didn’t mention efficiency in the video.
@tomasmcguinness , to be fair I've not run it that high as I'm a tight northerner 🤭. I should have by now, and will do next year, upgrade the rads. However I've balanced them as best I can and managing a 10°C flow/return Dt. It's a shame I can't go ASHP as it would fit nicely with a newly installed solar system! Keep the vids coming, they're very informative 👍.
You are right and thats a good rule of thumb. But with both temps I tested worth, the boiler actually operates in condensing mode. The measured efficiency doesn’t really differ between the days I looked at.
Even when using the low flow temperature though, why not use a thermostat set at, say, 20c (or whatever your preferred setting) and whenever the room reaches that temp. the boiler will switch off, saving even more money? I'm actually experimenting with adjusting the anti cycle time, I've set the boiler at 50c which easily gets our room up to 19c but with a 20 min anti cycle time. Setback temp. is also the key, certainly no need to have overnight temp. the same as the day, but a 2c difference works (for us anyway). On those 2 days in your example, we used 66 and 69 kWh respectively, 3 bed terraced house, 3 adults and also included cooking/showering (obviously yours is a bigger house).
I do have a thermostat with the low flow temp, but it only comes into plan when the outside temperature is above 3 or 4. This is because my boiler can modulate down low enough to provide the right amount of continuous heat. Once the temp is up at 8 or 10, the thermostat does kick in, turning the boiler off. Restarting the boiler during the on/off cycles can be expensive as the boiler will fire at max power when it turns on. I've limited this to 50% of its total, but that's still 17kW. I have individual temperature sensors in each room, but I take an average of the whole house rather than one specific room. My house is a 4-bed detached property and its heat loss for -3 is around 7.5kW
@@tomasmcguinness So, what is the length of your cycles ? My WB also has a hysteresis setting where it allows the water to drop below a certain temp before refiring. I'm unsure which takes precedence though, the hysteresis temp or anti cycle time, apparently you use them in conjunction with each other but when I contacted WB for an explanation they said leave it at default and high flow temp. (which is obviously a waste of money and gas).
My hysteresis is +/- 6 degrees (default), which I think is too wide for the lower flow temp. When the weather is warming, the flow temp does hit the plus 6 and the burner stops. This is mostly because my boiler is too large :( From what I understand, it's a combination of both. If the flow temp drops below the hysteresis point before the cycle time ends, the burner won't fire. I think anyway :) I plan on tinkering with those setting in January, to see if I can even the indoor temperature (it does climb as the flow temperature climbs)
@@tomasmcguinness Mmmm similar thoughts to mine. When you say too wide, do you mean it should be a less number i.e 2c on the hysteresis rather than the default of 6? Although I thought the hysteresis was only changeable for dropping the temp i.e. if I have a flow of 48c it goes up 4 degrees to 52c before then either cycling down to the hysteresis of (say 6c) or the set anti cycle time. Surely if the hysteresis is too wide (and you need a less of a drop) then the cycle would be much quicker? Mine drops 6 degrees (to the hysteresis) in about 4 minutes, if I set the hysteresis at 1 degree drop, then it would only be around a minute before restarting?
Hysteresis works both sides. If my flow is set to 45, the boiler will let it climb it 51 before turning off the flame. The water will continue to be pumped around the system until it falls to 39 at which point the flame will start again. That's my understanding anyway!
There is one huge reason you are not mentioning at all in your video. I assume you are using a high efficient condensating boiler. One big issue with high input flow temp is that the heat recovery in the boiler gasses is NOT working at all when your return flow temperature is 53 celsius or above. A Delta T of about 10 to 15 percent is what you are looking for. With 55 degrees input, you would get about 46 to 47 on your return temp. If you input 70 celsius, you would get somewhere around 59 degrees on your return. The loss in efficiency in a gas based heating system that's unable to do exhaust gas condensation can be up to 30%. Your loss in efficiency with higher temps is due to exhaust gas condensation just not working and you are thus piping a lot off heat out of your house. Obviously the 53 degree limit is influenced by the exact dew point of the exhaust air, which is a function of several complex inputs. If your house can get comfy with 55 degrees, that's a perfect sweetspot to go for, because you still have about 50% of your radiator capacity if you would run those at 70 degrees, AND you are guaranteed to have maximum condensation happening out of your exhaust gases. What a high efficiency boiler does, if possible, is preheat the return water with the heat still available in the exhaust gases. But for that to be able to occur, the water in the exhaust gas should be able to condensate. A phase change is a massive heat sink. For example, take a litter of water, frozen at 0 degrees. The amount of heat to turn that ice into a liquid is the same as getting that liter of water to boiling point.
Oh and if you want to know if your boiler is condensating properly on the return flow. A white plume outside indicates you should look to decrease your return flow temperature if possible. Even when it is freezing, and you are able to condensate on your exhaust properly, there simply should not be a white plume from your exhaust. Except when you turn on the shower for example, with a combi unit, flow stops on your heating system when you are producing hot water and thus there is no water to condensate the exhaust gasses with.
Thanks for your comment. Whilst I should have mentioned it, I didn't, because I don't believe condensing is playing a part in the lower consumption. On both of the days I looked at in the video, my boiler's efficiency is up around 90%. On the 70 degree days, the return only crosses the 53 line twice, for very short periods of time. You can view my boiler's statistics here - emoncms.org/app/view?name=TomsBoiler&readkey=484aa317fd15cfef28cc3c7a7a2bedd4 if you want to drill in more!
The boiler is a 35kW beast and its minimum output is supported to be 5.2kW, but I've never seen it that low. It's usually around 5.6kW. That was part of the reason I waited for the temp to drop below zero because it's only around then that the boiler becomes the right size.
@@tomasmcguinness Okay. Ours is 6.1 kwh at minimum. Mostly it's going on and down 7 times an hour. I see 7 huos in homewizard app (smart meter). In the morning it has to go from at minimium 16 degrees to 20,5 degrees. And only than it makes ongoing run. I have set the max power to 30 % (from 0 to 100). And temp to max 65 degrees(i think).. I let the modulating boiler in combination with the honeywel modulation thermostat do the rest !
Range rating, like you have done, is a great way to limit the damage of cycling. Honestly, before I learned anything about heating, our boiler was eating over 220kWh a day! Now, with the low flow temperature and range rating, the most I'll use in one day (if the boiler is only *all day* is about 150kWh) I was also burned by having Tado controls, which had no modulation support. At least you've got the right sort of controls. I don't want to buy new controls, as I'll be getting a heat pump in the next year or two. I think it would be throwing good money after bad.
@@tomasmcguinness One other question. Why is it and how,.. do you measure in kwh's with gas use. Because, here in the Netherlands we only measure gas in kubic (m3).. ? I know it's also in watts in Germany.. I read it on internet everywhere..
Here in the UK, we pay by the kWh. Our meters record m3 (as it's a gas!!) but it's converted to kWh on our bills. What part of the Netherlands are you from? I lived in Enschede and Maastrict when I worked for CMG back in 2000s,
If you have a modern boiler it should support open therm if you pair that with a nest thermostat + heatlink you can connect the heatlink using 2 wire open therm control and control the temperature modulation from the nest (can set the hot water as well)
That is very true. My boiler is only 3 years old, but as it's a Worcester Bosch, there are no 3rd party controls available that can work digitally. As I'm planning on having my boiler replaced by a heat pump in the next year or two, I'm reluctant to buy any new thermostat hardware.
@tomasmcguinness nest should work with it as long as boiler is opentherm (ot) if not be a bIt odd as its been a thing for quite some time (some boilers you might have to set it to open therm) What is the model of the boiler most boilers in last 6-4 years should have it
@@tomasmcguinness Not only do WB not support opentherm, Worcester own smart controller Worcester wave doesn’t support multiple zones, they’re not any more reliable than cheaper boilers and are a pig to work on, Worcester boilers truly are a triumph of marketing over substance.
@@tomasmcguinness but what about using a tado as they support other data bus types (it's nest that only supports opentherm as far as i am aware) tado supports HT EMS UBA BS WOLF KM E and opentherm and probably others not listed here Worcester-Bosch seems to be HT-bus if it has data bus connector (just set it to D17 on the tado Config id).
Some very cheap £30 thermostats have some advanced features, not always ON by default. I'm not sure a 2 day test will show the "benefits" even a basic digital thermostat Honewell DT 92e learns the boiler response over the previous 7days to optimise the boiler run times.
@@551moley There is also passive heating to be considered. I have a room where I switch my heating off when i go to sleep and then in the morning I check how far the temperature has dropped. Today and yesterday had similar outside temperatures, but today the sun was shining and the radiation was acting as a greenhouse effect in my room. The temperature was 2C higher in the morning because of this.
I get solar gain in my office and kid's rooms in the morning, which does help, but during the winter it's not all much, especially around this time of year, due to the orientation of the house. More so in the shoulder months.
I can see overall savings when running a boiler constantly at different flow temps but if you are switching off over night you would have to pump a certain number of kilowatts back into the house fabric to get back to desired temperature so not really a valid comparison?
I tried to replicate the starting conditions for both tests. The heating was off when the boiler started. In the test runs, the fabric would have been at roughly the same temperature. You said it's not a valid comparison. How could I improve the experiment?
It's a four-bed detached house. Around 150m2. The itself house is actually pretty well insulated, but being a 1950s build, it's draughty in places! When the temperature is around 0, we need around 6kW to maintain 20 degrees. Over the 19 hours that's 114kWh of gas. Add boiler efficiency into the equation and the figure is around where I'd expect it.
@@tomasmcguinnessyep, drafts will cost you much more than heat loss through insulation. Looking at your graphs and comparing them to mine you do seem to lose a ton of heat. I’m in the middle of insulating my place and had a new flat roof put on that leaks air like a sieve as it’s a cold roof and the insulation is not in yet. I have an old non condensing boiler so flow temps don’t help me at all but I’m out all day and most of the evening so heating the house would be a waste. So for me knowing my warm up times allows me to pre warm the house with the smart heating. Eventually I will swap the boiler out when I re-plum the radiators as they have their pipe work all buried in the concrete floor.
Drafts are next on my hit list! I have some that I can't even explain, like under the skirting board in my upstairs office. I'm going to get a door blower test in the New Year to see how leaky the house actually is before I work out how much time and money to put into air tightness. Good luck with the insulating!
@@tomasmcguinness Drafts sould be higher on the list than insulation. Even bricks insulate better that any open connection to the outside air. It's like wondering why the room is cold, while the door is open.
Hi Tomas. Great to see your low flow temperature experiments. We have recently done a similar thing with advice from a Heat Geek engineer. Before we got his help we were running our ridiculously oversized boiler with flow temperatures suited to radiators, even though we have UFH throughout. We have never really understood how to get the best from the system until we got advice from Leon. He removed a pump from the manifold and changed our zoning set up to open loop using the boiler pump and weather compensation. Our flow is set at a max 45deg, but often runs lower. This is our first winter with the new set up. We are comfortably warm and no longer turning the heating up and down. We run the system from 3 am to 9.30pm. I was nervous when we had the first snow in November but the new set up worked a treat and cheaper to run than our previous on/off set up. Look forward to move videos on your journey to a ASHP as we want to make the same transition.
I’ve been tracking our gas usage over two winters now. We have been using a flow temp of 50 degrees and as we are both at how all day, this year we have basically had the whole house at a constant temperature all day and night. Not only have we been consistently using less gas than lat year, we also haven’t had to put up with the house (especially downstairs) being cold for the first couple of hours in the morning
This is exactly what I'm talking about! Comfort and less cost! Thanks!!
Apparently that is the magic number, 50c, coincident I arrived to that number too. after study the basic how the boiler do condensation and the saving tipping point value. I put my thermostat at 17.5c "
@@tomasmcguinness this discussion has prompted me to look back at the historic data in our Tado app for the heating zones, how much temperature variation there was and how much time that zone was calling for heat. It’s really quite surprising how much more effective it is to aim for a constant temperature, especially as it’s more comfortable and the system isn’t chasing a constantly changing target.
Had a similar result. Last November ran boiler @ 50 degrees between 16:00 - 21:00 each day and used an average of 23.9 kWh per day. This year tried it at 36 degrees flow and had a set back of 18 degrees over night and then 19 degrees first thing, followed by 18 degrees during the day and then 19.5 between 16:00 - 21:00. We used an average of 45.37 kWh per day, keeping the house nice and comfortable 24/7. Noticed a massive reduction in condensation.
Brilliant. Condensation is an interesting one. If the fabric of the building stays warm, there aren't as many cold surfaces for condensation to form on. Of course, if the building cools down enough, you will get condensation again. If you're getting a lot of condensation, I'd look to identify the source and maybe look at ventilation changes.
@tomasmcguinness we have a bungalow with a loggia conservatory on which is unseparated, which doesn't help with the condensation.
@@JOOI525 PIV units are your friend...we have one and our humidity has gone from a regular mid/high 70's to low 60's, cheap to run too.
Something is odd here, last year you said 23.9 kwhr per day at 50 Deg and now you run at 36 for a longer period and use almost twice the energy at 45.3 kwhr. Is that a benefit? I can see why the condensation reduces but why do you have any condensation in the 1st place and where? But it's at almost twice the fuel cost,.......... Or have I misunderstood your savings ?
@stevew9957 OK, here goes. 2023 boiler running 5 hours on an evening. No heating on from 21:00 until 16:00 next day. House cold, trying to save money. This year tried it where heating on to maintain a minimum of 18 degrees over 24 hours, with 2 periods where it increases to 19 and 19.5 respectively. So home heated 24/7 as required. But only 22kWh for additional 19 hours of heat and comfort. Condensation is more of an issue in bungalows, ours is made worse by having a conservatory. So when you have no or little heat the air can't hold the moisture and this condenses on the glass. Hope this helps.
We have a smallish 3 bed semi detached built in 2018 but it does seem pretty well insulated. Peak gas used through days with with snow and about -2 outside including cooking and hot water is never more than 50kWh per 24hrs
I'm in a 1950s 4 bed detached. My heat loss is up around 7, so with the heating on for 18 hours a day, I require about 120kWh a day.
Have had my gas CH on various temps 24/7 for 20 years and, with good rad & room stat controls, found this to be the most efficient way to heat a 4 bed detached house and now a 4 bed bungalow. Boiler flow temp is kept at 55 degrees on my Greenstar CDi system boiler, bedroom rad stat at 2/3 with hall & livingroom at 4/5.
Anything at 55 or under is great, since your boiler will be working more efficiently. Not a fan of TRVs myself, but if it's working for you and your comfortable, it's working for you!
Great, interesting but complex subject, some points for consideration as well, electrical consumption of the boiler is related to run time of boiler and also optimisation is affected by flow temp i.e. at the higher flow temp the start time should be later in order to reach room temperature at the start of the occupied period and the stop earlier because of greater residual heat content which you did of course acknowledge at the end.
Thanks. It's very hard to account for everything in tests like this and they aren't the most controlled environments either, but it's interested to see broad results.
Interesting stuff Tom. Very informative. Actual house with figures! Love it. If you ask 'Google' it says something like 33KWH a day average, and I think - how? I'm in a 1934 bungalow, cavities and roof insulated, running a 40 year old fanned boiler set to 50c on Y plan F&E system with a delay unit to control firing, set to 12 minutes delay at the moment. On 14 hours a day and consuming about 55KWH a day with cooking and hot water. Seems to work. Of course I then think would a new Combi save me money? Or the glories of a Heat Pump that we see folk telling us they are so cheap to run whilst dressed in their thick woolies! Keep up the great content. 😊
Thank you! Glad you found it interesting.
If you average out gas usage out over the whole year, the daily number is rubbish. Average UK gas usage is 12,000kWh annually, which is your 33kWh a day. Doing that to my usage is only 43kWh a day.
Upgrading from a 40-year-old boiler would see you saving money, as condensing boilers are more efficient, especially with a flow of 50c.
Heat pumps do work perfectly well but need due care and consideration when being installed. They are not forgiving of poor design or installation.
hi john how far are the water runs to the kitchen and bathroom to the tank, do you leave the hot water demand on all the time or just set on a timer say twice a day.
@stephenfanthorpe2708 Hi, quite a long run from hot cylinder to the taps, as in most F&E systems but have an electric shower. In summer two times sessions for hot water but when heating is on so hot water priority is the rule, no hot water off -but - I've fitted a HW off switch to boost heating if needed. (A DPDT switch overrides tank stat)This because I've also fitted a delay unit (555 timer ic) to delay firing. It works for me, and boilers only half my age, but I guess a combi has got to go in one day!
@ I find often in bungalows in the loft as close as central to the bathroom/s kitchen is ideal if you go the combi route just for less lost time getting to temp at the taps especially if you use a lot of 2minute water. If you have currently say a baxi solo or an ideal classic boiler you’ll be looking at 25% better efficiency minimum m. If you do go combi ensure they match the hot water output to your mains water flow rate a 30kw with 12l a min flow capacity isn’t as efficient as a 24kw with 9l if you only have 6l a min flow to play with. Condensing boilers need to condense to be as efficient as the tag. Calculate the heat loss per room get the radiator capacity and your water usage that is the way to plan it properly to save money hit a delta of 40-50 and you won’t believe how cheap a boiler can be to run in comparison even the one you have now. I think maybe your rads are somewhat small or you maybe haven’t enough carcass in the pipe work to keep it efficient as it could be.
Heat pumps are good and have about the same running cost as efficient gas if reasonably installed.
The benefits to me are the reduced emissions and the modern heating controls, which are good, being more sophisticated than my old gas boiler. It should also never need upgrading (will need fixing and might need replacing at some point). My solar, battery and time of use tariffs are what help bring the cost down below what I had previously (as they would had I kept my old heating system).
5 bed house, integral garage. Run our heating at 36 degrees day and night, even in the cold snap. We have 10mm microbore drops to radiator. No heating in the main bedroom. We got a good drop in bills (still on old meter) and for 4 adults inc 2 gamers our bills are £10 more per month than our neighbours in the same house config - run their heating only morning and evening and retired but also out a lot. Happy with that
I do have some more tweaking to do re pump speed and other bits.
Houses are predominantly sold block walls - very little studding so I work on keeping thermal mass in the house
36 degrees! My house is at 19, if it ever gets above 20 we all start cooking.
@@StephenButlerOneheating water flow temp, not room temp
That's great! 36 is really good and shows microbore isn't the end of the world either. I really need to find out what my street uses in terms of gas. I've been pondering a survey or some type to share as I'd be fascinated to see how my usage compares!
@@tomasmcguinness I watched an Urban Plumbing video that opened my eyes to it. Funnily enough it was done while he was putting in UFH for going to a heat pump and he showed running a low flow temp to heat his house while it was sub-zero outside .
He also helped (via email) with selecting our Intergas Boiler which has so far been fantastic.
@@tomasmcguinness could heat a house with a candle if it beat the heat loss off the house!
I've had a look back at some of your previous videos and found that you have a 2 storey house of about 150m2 total floor area? Can I ask if the overall structure and insulation is typical of your area? It's just that I'm utterly staggered by the energy consumption, our approx 150m2 bungalow in the north Highlands has a maximum 24hr heating consumption (space and DHW) since I started measuring it in 2017 of 33.9kWhr, that was on January 18th this year when the outside temp was -7c and the wind 50mph+. I measure all the energy going into our thermal store from the heat pump, solar thermal and solar diverter, so can't split out the DHW. We do get much colder weather, but that tends to be very still so heat loss is actually lower.
I keep hearing that the UK housing stock is badly insulated, but never realised a typical family home owned by someone actively try to reduce energy consumption would be consuming over 100kWhr/day with the outside temp hovering around 0C. I find that a bit depressing really.
What?? That's crazy!! 34kWh for one day when it was -7 outside?? That means you were only putting in about 1.5kW of heat over the whole day?
You're right about the house, 4-bed, detached. Heat loss is about 7.5kW for 21/-3, so to maintain 21 over a whole day would be 180kWh.
My house is better insulated than most on the street. It's a 1950s, with suspended floors and cavity walls. I have insulated the floors, the loft and even had cavity wall insulation added. I know that's more than most of the houses of the road.
I am going to try and survey my neighbours in Jan/Feb to get a feel for energy usage on the street and see how mine compares. Usage pattern is important to consider too. We're working from home all day, so we will have the heating on more than those who are out at work.
@@tomasmcguinness Yes, 1.5kW in those conditions is about right, the heating is at 21c 24/7, except the spare rooms where it's 18c if no visitors. Over the last 12 months to date we've put 4081kWhr of heat into the thermal store from all sources, I estimate 1400kWhr is used for DHW so about 2700kWhr for heating.
Our house was built 20 years ago, it's a 140mm timber frame and suspended floors, 140mm PU in both plus 20mm over the complete wall to minimise bridging then Fermacell to finish. 40mm PU on the window and door reveals. 40mm PU under the floor for anti-bridging. 400mm Rockwool in the loft and eaves "fences" to prevent cold air being blown under the insulation. MVHR, triple glazing and I was pretty obsessive about sealing every little gap. The trades helping me thought I was mad to exceed building regs requirements, at that time oil was maybe 12p/litre, but it was as much about comfort and only added about £7k to build costs
Leak tests weren't required at the time but I do them periodically using the MVHR, I can do both positive and negative pressure tests by blocking the inlet or outlets as necessary and turning the opposite fan to maximum. Typical results are 20litres/sec at 15Pa for the entire house, that equates to around 1.1 air changes per hour at 50Pa, so nearly double that allowed for Passivhaus but well above current building regs.
I have a comparison with a friend's house, similar size bungalow to ours and same age but built by a developer. They're still on a condensing oil boiler and use around 1100 litres/year, it's probably around 85% efficient so that's 9600kWhr in total, assume 1400kWhr for DHW therefore 8200kWhr for heating; or 3 times our heat requirements.
One caveat with low flow temperatures - the radiators need to be big enough to dissipate the minimum modulated burner output. If the heat demand is below that the flame will cycle on and off; would welcome any data about that affects boiler efficiency (from recent YT videos it seems to have a bad effect on heat pumps).
PS - My Y Plan system uses the same boiler temperature for heating and hot water. As such, the lowest I can go to get usable hot water is 55 C. Between Spring & Autumn my solar panels add extra heat to the water so I can go lower but there is precious little sunshine this time of year.
My boiler is so big, the minimum is between 5kW and 6kW. I asked the plumber to put in some oversized radiators, thought I didn't even know what that really meant at the time.
The hotter the radiators, the more heat they will output, but as I show, when it's zero outside, a 40 flow temp is still enough to get the house up to 20ish. Last winter, when it was -5, a 45 flow was enough.
Heat Pumps really don't like cycling. It's far more inefficient then a boiler, so good design is important to ensure the heat pump is correctly sized. If my boiler was 20kW and could modulate down to 2kW, it would *never* need to cycle.
I have an S-Plan system, but was able to jury-rig support for two flow temperatures, so I can use 70 for hot water and anything else for heating. There are a few videos in my channel on how I did it.
Didn't expect the F bomb at 50 secs, the kids loved it while I was chilling on the sofa with them!
Sorry! I was going to bleep it out, but I felt it ruined the delivery of the quote!
I run mine at 52c and it's on timer, runs around 7 hours a day, 4 bed end terrace 1950's house, well insulated, using around 30kw a day of gas and then I light my wood burner at 6pm. Wood burner is essential when it's sub zero in an older house as before that I could use 140kw of gas a day in a cold snap and it would be chilly in here, now T shirt in the evening.
Does any boiler running 24/7 not cause an additional charge for electricity and wear and tear which may off set gas savings?
Good question and I have wondered this too. Electricity usage isn’t all that much. I monitor this and if my boiler was running for 24 hours solid it would use about 1kWh of electricity. Wear and tear - not sure. I have heard that restarts cause more wear than continuous operation. There is also much less thermal stress & shock since pipes, joints etc. stay at a steady temp. I don’t have any empirical evidence for this, just what I hear from professionals.
@@tomasmcguinnessthanks for the reply and considerations👍
Great video and data. Could you compare a day when you go out with a heat in the morning, off all day, then heat in the afternoon/evening before you get back? It'd be good to see how much the efficiency cancels out the saving from the lower delta loss. Your indoor temp was slightly higher on the thermostat day, so I guess a lot of the extra energy was due to the delta to outside. Comparing my octopus figures on the same day, I guess your house is a lot bigger than mine 😮
Would that with the high flow temp vs the low flow temp?
And you're right about the set point being high. We find that when the heating isn't on (i.e. the boiler isn't firing), we *feel* colder, so I set it at a higher value. That said, the outdoor temperature during the day was *higher* so the internal/external dT was probably less. I need to add a sensor to track the dT as that would be useful.
House is a four-bed detached property with a 7ish kW peak heat loss.
@ yeah on the high vs low flow temp. The warmer temp makes sense to feel the same warmth if there isn't as much mass giving off stored heat. dT vs COP would be a good comparison when you get a heatpump. I'm in a 3 bed detached, but not much distance between the houses, and with a low flow temp it has taken a while to heat up.
Hello Tom I notice your consumption for that cold period is high do you use other gas appliances?
On 19Nov (-1c) my baxi duo tec 24 combi used 81kwh.
On a regular day with outside temp at 5c I use just below 60kwh per day. I live with family of 4 in a 1950's semi detached 3 bed 100m2 my flow temperature at 45c to get my house to 22c from 5am to 10pm. All Trvs but room with thermostat set at 4 throughout.
I don't think it's too high for the property. I live in a 4-bed detached house, around 150m2, so my usage at around 120 is proportional enough to your 81. Peak heat loss on my house is about 7.5kW when it's -3 outside, meaning I'd use around 140kWh on a very cold day with the heating running constantly. I have *no* TRVs in the system, since I don't believe they bring any values.
I don't know if this is covered in other videos, But this would only be condensing boilers.
A condensing boiler condenses the water out of the exhaust, which extracts more heat, but if the temperature is too high, it condenses outside, losing energy. So that cloud of smoke you see coming out of boiler flues, is actually steam, and thats energy a condensing boiler should be capturing.
heat pumps should also be more efficient at lower flow temperatures, but for different reasons.
I don't think there is anything stopping a *non* condensing boiler running with a low flow temperature. I know must older boilers had to run at 80 to stop corrosion and that choice of temp was carried forward to more modern boilers. This is part of the problem with most default flow temp settings today.
@@tomasmcguinness You can run any boiler at a lower flow temp. You aren't going to see any benefit.
A condensing boiler uses less energy because it condenses. a lower flow temp means you will be able to condense more water out of the exhaust. None of this is relevant to a non condensing boiler.
Of course it is. Running a lower temperature will use less gas. I’m trying to show that you can run all day at a low temp and use less gas than a high temp. In both of these cases, my boiler’s efficiency is pretty much the same. It just takes less energy to heat water to 40 than 70.
@@tomasmcguinness Wheres the saving coming from?
assuming youre heating your house to the same average temperature, you aren't losing less heat from the thermal envelope. and gas doesn't burn more efficiently at a lower temperature
See for example ua-cam.com/video/wFOpHNz7Fdc/v-deo.html specifically around 4:12
Running longer at a lower temperature consumed less gas the high flow temp. It’s not a perfect comparison as the weather was warmer.
In the video you refer to, Szymon is talking about efficiency. I’m looking at consumption.
My boiler is operating in condensing mode in both of these tests, since the return temp stays below 55. If you look at the blog post, I address efficiency in its own section.
I see from your graph that your indoor temperature during your high temperature flow was a little higher than during the low temperature day. It's difficult to see exactly, but it looks like about 2 degrees warmer on average throughout the day (something like 21 vs 19). If it is that much, this would account for quite a large amount of heat input, I would suggest.
Secondly, 21C is really warm. You could save messing aroung with flow temperatures by turning your thermostst down and wearing a jumper.
Well spotted! Under thermostat control, the set point was 21. It has to be higher to make the house feel as comfortable, since the boiler is stopping and starting. The outdoor temperature is also higher on that day, so the delta is about the same.
Having the heating on all day means the indoor target temp is lower, yet we feel as comfortable.
We do wear jumpers anyway, as that just makes sense in colder weather. If we were walking around in t-shirts and shorts, the set point would need to be even higher.
you could look at mean temp difference (inside - ext) per day vs gas usage per day to get an efficiency metric?
I use influx to record that data and grafana to graph it summarised by week.
I’ve actually added a sensor to record that after doing my test. Great minds!
Totally agree with this I got the same result with my 15 year old baxi 33kw combi. I tried to run it at 40 but it short cycles so the lowest it is happy to run is 50 but that does the trick and keeps the house warm without excessive bills. It is also useful to know the flow temperature that I will need for when I get a heat pump.
That is one of the reasons I'm experimenting with temperatures as I want to get a heat pump in the next year or two.
Same here - my Baxi can only modulate down to 9kW and so anything lower than 50C the rads can’t get rid of the heat and short cycles - in principle a HP of a similar size will match my heat loss at -3C and can the compensate up to 50C as and when needed 👌
@@tomasmcguinness this our plan as well. We’ve had solar and batteries for about 18 months now and even with gas heating and an EV we are not far off being cost neutral over a full year. The only part of our house which may need some plumbing changes is the downstairs front hallway. It s north facing and the coldest part of the house. Layout means there’s only limited radiator space and although there is a good size 1800mm tall radiator, in fitting in very small pipe has been used (8mm copper) and I don’t believe that 8mm can carry enough energy at sensible flow rates to keep the hall warm. A new, very efficient front door and triple glazed side panel are going in and may solve this but otherwise we will have to have bigger pipes chased down from upstairs. Still, gives me something to do I suppose.
The question to answer is, where does the excess energy go? Because if the house had the same comfort levels on both days there must have been increased losses. My guess would be increased flu losses due to increased output. If the space temperature remained the same then the fabric losses should have remained equal for both scenarios. Any thoughts?
Good question.
At this point, I believe it's all down to the ferocity of the burn. The boiler won't start modulating its power until the flow temp is at the desired level. It burns like crazy to get the water up to 70. It never does because the house's temp gets pushed up and the thermostat tells the boiler to turn off. It's related to my boiler being oversized too. I have limited my boiler to 50% of its max, so when it starts, it's putting out about 18kW before it starts to reduce its power. It burns like that 10 times in the day. With the lower temp, it has a large burn at the start, but the water reaches 40 very easily (as the water starts at 15) and once it's up to temp, the boiler throttles all the back to its lowest output.
The temperature on the high temp day also fluctuates, up and down, as the thermostat tries to meet the desired temp. On the low temp day, the indoor temperature slowly rises to the desired level and then flattens and remaining constant.
@tomasmcguinness that explains a lot thanks. All of the energy must go somewhere so if the room temperature fluctates above the desired setpoint the delta between room and outside will be greater which will lead to increased fabric losses at those times. Gas burns at the same temperature regardless of the water flow setting, which is likely to equal greater flu losses when the boiler is operating, though it seems like the boiler is range rated. Either way look into the benefits of compensated heating control, which will increase radiator temperature in winter and decrease radiator temperatures in milder conditions. If you combine compensated heating with a condensing boiler you'll also reduce the boiler flu losses. Until then it looks like your heating system might be oversized, which is a good thing and allows you to operate a lower 40*C radiator temperature setting even in winter.
Great experiment and I really enjoyed the video. Thank for putting this together Tomas 👍
Is this just balancing the reduced heat loss from the house being cooler while you're out, vs reduced boiler efficiency when run at full power?
If your house is well insulated and has lots of thermal mass, it won't cool down much while the boiler is off, and will continue to lose heat at close to the normal rate - and low-and-slow will work well. OTOH if your house cools down to ambient when you turn the heating off, it will stop losing heat entirely and an on-off strategy would work better.
I'm not really sure what affects boiler efficiency. I'd imagine there's a critical power where a condensing boiler's exhaust it above boiling point and your efficiency drops drastically.
I think it would be useful to plot heat loss and boiler efficiency, and model what happens in different scenarios.
if the higher flow temp was running the boiler flat out for a period of time to get the house temperature up to the desired target than does that mean running the boiler at the lower flow rate took much longer to reach the same desire internal temperature ? in which case one would assume the net gas consumption is the same albeit allowing some small difference ?
That's what you'd assume, but it turns out not to be the case. If you look at the graphs, the morning burn at 70 degrees used almost 60kWh of gas in the first three hours. The low burn used around 20kWh in the same period of time.
The boiler has to work *much* harder to heat water to 70.
Perhaps my experiment was flawed, but the data showed that across the whole day, leaving the heating on used less gas.
Not to mention the reduced stress on the boiler and system due to reduced expansion and contraction.
Exactly! Another one of the benefits of low temperatures!
but was there any difference on how long it took to get the house up to the desired temperature in the morning?
Yes, absolutely. Lower flow temperatures mean slower warmups. It's just something you need to account for.
the laws of physics tells us you use more energy to heat a house all day; heat loss wont be less bc the house is kept warm 24/7; the answer is always better insulation
That is true, but the rate of delivery of that energy is what I questioned.
Any thoughts on Thursday 21 with 162kWh?
On that day, the outdoor temp didn't really get above zero at all. I was running at the slightly higher flow temp of 45 too and the hourly consumption was a little over 8kWh. The startup usage was high as I think the fabric lost most heat because it was -2 for most of the night.
I tried this in my 1992 4 bed detached Mcleans house. It didnt work, for what i think are the three main reasons;
1. Some of the radiators/emitters are original whoefully undersized units piped in 10mm microbore.
2. The 2007 Baxi 40kWh boiler doesn't modulate sufficiently at 50C let alone lower temps, it cycles constantly.
3. Excessive heat loss.
The third reason is why I wont go for a heat pump! Ill probably try and bag a more efficient boiler.
Im surprised this test wasnt carried out with the boiler in condensing mode, ie return temp < 55°C. I think the results would have been closer.
Good on you for giving it a try!
If the rads are undersized at 70 you have no hope with anything lower :)
My boiler is 35kW so I feel your pain!
How excessive is excessive? Have you had a heat loss survey done?
My test? For the most that, the boiler was always operating in condensing mode. Even at 70, the return only passed 54 for two very short periods. That is why I didn’t mention efficiency in the video.
@tomasmcguinness , to be fair I've not run it that high as I'm a tight northerner 🤭. I should have by now, and will do next year, upgrade the rads. However I've balanced them as best I can and managing a 10°C flow/return Dt.
It's a shame I can't go ASHP as it would fit nicely with a newly installed solar system!
Keep the vids coming, they're very informative 👍.
The boiler operates more efficiently at lower temperatures, because more heat from the flame is extracted by cool water than hot water.
You are right and thats a good rule of thumb. But with both temps I tested worth, the boiler actually operates in condensing mode. The measured efficiency doesn’t really differ between the days I looked at.
Even when using the low flow temperature though, why not use a thermostat set at, say, 20c (or whatever your preferred setting) and whenever the room reaches that temp. the boiler will switch off, saving even more money? I'm actually experimenting with adjusting the anti cycle time, I've set the boiler at 50c which easily gets our room up to 19c but with a 20 min anti cycle time. Setback temp. is also the key, certainly no need to have overnight temp. the same as the day, but a 2c difference works (for us anyway). On those 2 days in your example, we used 66 and 69 kWh respectively, 3 bed terraced house, 3 adults and also included cooking/showering (obviously yours is a bigger house).
I do have a thermostat with the low flow temp, but it only comes into plan when the outside temperature is above 3 or 4. This is because my boiler can modulate down low enough to provide the right amount of continuous heat. Once the temp is up at 8 or 10, the thermostat does kick in, turning the boiler off.
Restarting the boiler during the on/off cycles can be expensive as the boiler will fire at max power when it turns on. I've limited this to 50% of its total, but that's still 17kW.
I have individual temperature sensors in each room, but I take an average of the whole house rather than one specific room.
My house is a 4-bed detached property and its heat loss for -3 is around 7.5kW
@@tomasmcguinness So, what is the length of your cycles ? My WB also has a hysteresis setting where it allows the water to drop below a certain temp before refiring. I'm unsure which takes precedence though, the hysteresis temp or anti cycle time, apparently you use them in conjunction with each other but when I contacted WB for an explanation they said leave it at default and high flow temp. (which is obviously a waste of money and gas).
My hysteresis is +/- 6 degrees (default), which I think is too wide for the lower flow temp. When the weather is warming, the flow temp does hit the plus 6 and the burner stops. This is mostly because my boiler is too large :(
From what I understand, it's a combination of both. If the flow temp drops below the hysteresis point before the cycle time ends, the burner won't fire. I think anyway :)
I plan on tinkering with those setting in January, to see if I can even the indoor temperature (it does climb as the flow temperature climbs)
@@tomasmcguinness Mmmm similar thoughts to mine. When you say too wide, do you mean it should be a less number i.e 2c on the hysteresis rather than the default of 6? Although I thought the hysteresis was only changeable for dropping the temp i.e. if I have a flow of 48c it goes up 4 degrees to 52c before then either cycling down to the hysteresis of (say 6c) or the set anti cycle time. Surely if the hysteresis is too wide (and you need a less of a drop) then the cycle would be much quicker? Mine drops 6 degrees (to the hysteresis) in about 4 minutes, if I set the hysteresis at 1 degree drop, then it would only be around a minute before restarting?
Hysteresis works both sides. If my flow is set to 45, the boiler will let it climb it 51 before turning off the flame. The water will continue to be pumped around the system until it falls to 39 at which point the flame will start again.
That's my understanding anyway!
Works for me also.....I also down rated my boiler from 24kw to 8 KW.
There is one huge reason you are not mentioning at all in your video. I assume you are using a high efficient condensating boiler.
One big issue with high input flow temp is that the heat recovery in the boiler gasses is NOT working at all when your return flow temperature is 53 celsius or above. A Delta T of about 10 to 15 percent is what you are looking for. With 55 degrees input, you would get about 46 to 47 on your return temp. If you input 70 celsius, you would get somewhere around 59 degrees on your return.
The loss in efficiency in a gas based heating system that's unable to do exhaust gas condensation can be up to 30%.
Your loss in efficiency with higher temps is due to exhaust gas condensation just not working and you are thus piping a lot off heat out of your house.
Obviously the 53 degree limit is influenced by the exact dew point of the exhaust air, which is a function of several complex inputs. If your house can get comfy with 55 degrees, that's a perfect sweetspot to go for, because you still have about 50% of your radiator capacity if you would run those at 70 degrees, AND you are guaranteed to have maximum condensation happening out of your exhaust gases.
What a high efficiency boiler does, if possible, is preheat the return water with the heat still available in the exhaust gases. But for that to be able to occur, the water in the exhaust gas should be able to condensate. A phase change is a massive heat sink. For example, take a litter of water, frozen at 0 degrees. The amount of heat to turn that ice into a liquid is the same as getting that liter of water to boiling point.
Oh and if you want to know if your boiler is condensating properly on the return flow. A white plume outside indicates you should look to decrease your return flow temperature if possible.
Even when it is freezing, and you are able to condensate on your exhaust properly, there simply should not be a white plume from your exhaust.
Except when you turn on the shower for example, with a combi unit, flow stops on your heating system when you are producing hot water and thus there is no water to condensate the exhaust gasses with.
Thanks for your comment. Whilst I should have mentioned it, I didn't, because I don't believe condensing is playing a part in the lower consumption. On both of the days I looked at in the video, my boiler's efficiency is up around 90%. On the 70 degree days, the return only crosses the 53 line twice, for very short periods of time. You can view my boiler's statistics here - emoncms.org/app/view?name=TomsBoiler&readkey=484aa317fd15cfef28cc3c7a7a2bedd4 if you want to drill in more!
How much is the low load (minimal) power of the boiler ?
The boiler is a 35kW beast and its minimum output is supported to be 5.2kW, but I've never seen it that low. It's usually around 5.6kW. That was part of the reason I waited for the temp to drop below zero because it's only around then that the boiler becomes the right size.
@@tomasmcguinness Okay. Ours is 6.1 kwh at minimum. Mostly it's going on and down 7 times an hour. I see 7 huos in homewizard app (smart meter). In the morning it has to go from at minimium 16 degrees to 20,5 degrees. And only than it makes ongoing run. I have set the max power to 30 % (from 0 to 100). And temp to max 65 degrees(i think).. I let the modulating boiler in combination with the honeywel modulation thermostat do the rest !
Range rating, like you have done, is a great way to limit the damage of cycling. Honestly, before I learned anything about heating, our boiler was eating over 220kWh a day!
Now, with the low flow temperature and range rating, the most I'll use in one day (if the boiler is only *all day* is about 150kWh)
I was also burned by having Tado controls, which had no modulation support. At least you've got the right sort of controls. I don't want to buy new controls, as I'll be getting a heat pump in the next year or two. I think it would be throwing good money after bad.
@@tomasmcguinness One other question. Why is it and how,.. do you measure in kwh's with gas use. Because, here in the Netherlands we only measure gas in kubic (m3).. ? I know it's also in watts in Germany.. I read it on internet everywhere..
Here in the UK, we pay by the kWh. Our meters record m3 (as it's a gas!!) but it's converted to kWh on our bills.
What part of the Netherlands are you from? I lived in Enschede and Maastrict when I worked for CMG back in 2000s,
If you have a modern boiler it should support open therm if you pair that with a nest thermostat + heatlink you can connect the heatlink using 2 wire open therm control and control the temperature modulation from the nest (can set the hot water as well)
That is very true. My boiler is only 3 years old, but as it's a Worcester Bosch, there are no 3rd party controls available that can work digitally. As I'm planning on having my boiler replaced by a heat pump in the next year or two, I'm reluctant to buy any new thermostat hardware.
@tomasmcguinness nest should work with it as long as boiler is opentherm (ot)
if not be a bIt odd as its been a thing for quite some time (some boilers you might have to set it to open therm)
What is the model of the boiler most boilers in last 6-4 years should have it
Again, no OpenTherm support on the WorcesterBosch I have. I find the state of controls a complete joke. OpenTherm should be mandatory.
@@tomasmcguinness Not only do WB not support opentherm, Worcester own smart controller Worcester wave doesn’t support multiple zones, they’re not any more reliable than cheaper boilers and are a pig to work on, Worcester boilers truly are a triumph of marketing over substance.
@@tomasmcguinness but what about using a tado as they support other data bus types (it's nest that only supports opentherm as far as i am aware) tado supports HT EMS UBA BS WOLF KM E and opentherm and probably others not listed here
Worcester-Bosch seems to be HT-bus if it has data bus connector (just set it to D17 on the tado Config id).
Maybe you want to use a PID controller.
The SAT thermostat I used for the test is PID controller. I think it needed more time to tune itself.
Some very cheap £30 thermostats have some advanced features, not always ON by default. I'm not sure a 2 day test will show the "benefits" even a basic digital thermostat Honewell DT 92e learns the boiler response over the previous 7days to optimise the boiler run times.
@@551moley There is also passive heating to be considered. I have a room where I switch my heating off when i go to sleep and then in the morning I check how far the temperature has dropped. Today and yesterday had similar outside temperatures, but today the sun was shining and the radiation was acting as a greenhouse effect in my room. The temperature was 2C higher in the morning because of this.
I get solar gain in my office and kid's rooms in the morning, which does help, but during the winter it's not all much, especially around this time of year, due to the orientation of the house. More so in the shoulder months.
I can see overall savings when running a boiler constantly at different flow temps but if you are switching off over night you would have to pump a certain number of kilowatts back into the house fabric to get back to desired temperature so not really a valid comparison?
I tried to replicate the starting conditions for both tests. The heating was off when the boiler started. In the test runs, the fabric would have been at roughly the same temperature.
You said it's not a valid comparison. How could I improve the experiment?
You are using a huge amount of gas - how big is your house? I think you might need better insulation.
It's a four-bed detached house. Around 150m2. The itself house is actually pretty well insulated, but being a 1950s build, it's draughty in places! When the temperature is around 0, we need around 6kW to maintain 20 degrees. Over the 19 hours that's 114kWh of gas. Add boiler efficiency into the equation and the figure is around where I'd expect it.
@@tomasmcguinnessyep, drafts will cost you much more than heat loss through insulation. Looking at your graphs and comparing them to mine you do seem to lose a ton of heat. I’m in the middle of insulating my place and had a new flat roof put on that leaks air like a sieve as it’s a cold roof and the insulation is not in yet.
I have an old non condensing boiler so flow temps don’t help me at all but I’m out all day and most of the evening so heating the house would be a waste. So for me knowing my warm up times allows me to pre warm the house with the smart heating. Eventually I will swap the boiler out when I re-plum the radiators as they have their pipe work all buried in the concrete floor.
Drafts are next on my hit list! I have some that I can't even explain, like under the skirting board in my upstairs office.
I'm going to get a door blower test in the New Year to see how leaky the house actually is before I work out how much time and money to put into air tightness.
Good luck with the insulating!
@@tomasmcguinness Drafts sould be higher on the list than insulation. Even bricks insulate better that any open connection to the outside air. It's like wondering why the room is cold, while the door is open.