Sizing Ductwork THE CORRECT WAY
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- Опубліковано 28 сер 2024
- Learn how to size ductwork the correct way. If you are still using 0.1" for a friction rate, you must watch this video
Video referenced
• HVAC Supplementary ...
Long Video for Architects, Engineers, Designers, And Service Professionals
www.SandwellMechanical.com
Sandwell Mechanical
717-549-3885
john@sandwellmechanical.com
Been fabricating duct in the shop for 11 years, and this was an extremely helpful insight into how things are designed. Definitely going to appreciate it moving forward in my career. Subbed 🤙🏼
I ran my own HVAC company for a total of 25 years, 18 of those in small town Iowa and it was a great experience. My wife kept the books and I did the work, having my son and sometimes my wife help me move equipment. I wore all the hats from scheduling the work, to doing the work, load calculations, duct sizing, choosing equipment, and, unfortunately sometimes having to collect the money the hard way (small claims court). Having said that, I would like to say that it is very hard for the single- person shop to compete with the BIGS (big companies) even if you do great work (I know I did great work because people told me I did). If you do everything they tell you that you need to do to "get it right' (and I did), then, if you sat down with paper, pencil, and a big eraser and figured out how much an hour you're getting paid for investing all of that time, you may as well get a job flipping burgers at Mickey Ds, it would pay more and you would have benefits; sad but true. The only other alternatives would be to charge the customer for all the time invested, or hire and train people to do the calculations for you, either one would probably quickly price you out of the running.
Okay, now that I got that off of my chest, here are some things to consider: 1) if properly used, you can't go wrong using this duct sizing methodology, since you will always get the most efficient duct system, and it even has a bit of wiggle room built-in. 2) know that this method also always yields the biggest, most expensive duct system and this will exclude you from the estimates that most homeowners will consider unless you can convince them that it is among the best investments they can make in their homes; one that could possibly last the life of their homes. 3) remember I said "could possibly last the life of their homes" and this is why: all it takes for the homeowner to screw this all up is : 1) for them to replace the air filter you installed with a way more restrictive air filter 2) cover up return air grilles and/or close registers (often done in the basement in the cooling season) 3) build on to the home without consulting with you about ductwork changes that will need to be made to accommodate the additional space and last, but not least, the ever popular 4) not replacing the air filter as frequently as you recommended ( I can't tell you how many times I discovered this to be the only thing causing the problem, and then they complain about you charging them to replace their air filter). Fortunately, I did have great customers who had a lot of patience and understanding.
Well, I hope this wasn't too negative, but it is the truth. You know, maybe I should have written a book instead of this comment. 🤔
Read all of it and i think its great man. Would love to know more
Say it brother. Everyone is in a race to the bottom. Cheap cheap cheap. Nobody wants their contractors to pay their rent. I quit and have the same lifestyle as when I worked minus the stress and 10 hour days. Old clients still call and I just laugh.
I agree with you. The manual D calculates everything as you can see. It also runs you through velocity design and return velocity design. You will see that usually when done right you can barley hear return and supplies. You can actually flow the same amount of airflow at higher velocities with smaller duct but there is a limut to the blower performance. As a contractor you have to make sure not to cross some of this limits. For example dont run a 4 ton unit with a 12 " return amd we all know we run into some rigged uo unit where someone gas done this. I agree with you. For the most common small residential home the common evailable static is usally close. Just have to rememember to also keep corrrect size boots and return. It keeps you in tje ball park but not precise as the manual D. I worked commercial for 10 years and yes commercial has all kind of money where they can afford an engineer to do the design from the load calc to duct. Its not uncommon to charge 100k for a 10 ton complete system. 😂😂
Finally someone that cares about the work they do. Great Video. I just started my own HVAC business and my goal is to be different then all the .1 guys around here and do things the correct way. Thanks
One of the best videos on duct design that I have seen so far. Relative to the mechanical side of the trade, I think that ductwork and duct design is probably one of the least understood topics. I have 35 years as a technician in the trade and been teaching now for almost 7 years and duct design can be a bit difficult to teach in a limited amount of time. For that and other reasons, I think that ductwork, especially residential is also one of the most abused parts of the trade.
More comprehensive than my semester long ductwork course. Thank you.
Glad it was helpful! Thanks
Honestly, this really should be a 3 hour video. There's so many questions i have
Honestly, it was 3hrs. I cut much of it just to maintain some audience. What is briefly covered here could be a 3 week course. Thanks for the watch!!
In a perfect world this is great. Man I wish we lived in a perfect world.
Good info to take note of.
So many hacks out there cobbing jobs that haven't a clue. When you first look at a job, if there are no ports for static pressure monitoring, be leary.
I've been involved in HVAC since the late 70's. Was asked to leave my job as maintenance supervisor in my mid 20's to join a large union sheet metal contracting outfit that was founded in 1867. Our systems were in the Pentagon, many government projects, schools, factories, institutional and industrial projects across the country. We had an entire floor of engineers and draftsmen. I was blessed to have had opportunities to work with some amazing folks in research and development with many large corporations. Our larger systems had fans big enough to crawl into and pretend that you were a gerbil. We had the as builts for every project. Built and serviced many of the large theaters and opera houses. Was an interesting career. I was also involved in fire, EMS, cutting people out of what was left of their vehicles,
dive team, tech rescue, and flew occasionally with the early medical helicopters and the first non hospital based EMS helicopter in the country.
I often joked that I did this to unwind after dealing with architects and engineers.
It never ceases to amaze me how many folks have blinders on -- they just don't look at the whole system.
I was recently asked if I could help a friend change a compressor on a second floor factory office rooftop.
In talking with the head of production of the factory, he mentioned that he didn't understand why they kept losing compressors.
I surveyed the systems. Contacted the owner who had been involved with the original construction of the building. The owner sent me original prints. There had been problems since the building was built. Two additional split/dx systems had been added to the south end of the offices. They had cobbled into existing duct, and added spaghetti warehouse flex runs draped through the ceiling -- too small of duct for the new systems and further exacerbated the problems with the other units. The original prints showed devices with up to 16" necks. The largest device necks in the building were 8". The static pressures were literally off of the chart. So many other projects where larger equipment had been quoted but the duct couldn't support what was there. Explaining problems like this has led to an abundance of work without ever advertising.
I have done surveys for home and building owners, realtors, and insurance companies.
Superintendents and building/ business owners have become friends once they saw that looking out for their project and capital was a priority. Have open invitations to friend's properties on lakes, golf courses, in the Allegany mountains, in Idaho, West Virginia, Virginia, Colorado, Florida, and Mexico, etc. -- do all you do as if you're doing it directly for our Creator. It comes back to you.
Very nice! Thanks
Thanks for posting this. I feel like this is probably the most misunderstood thing in the industry. Lot of companies I work at just go by the .1. One of my mentors told me 0.8 supply and 0.6 return. I see it is a lot of work to do it manually if you don't have the program.
Yes friction rate is calculated not guessed.
Thanks to its details and its length, here's a video you can really learn something from.
Thanks I appreciate it
Great video, thank you! In my mind, the concept of Friction Rate is squirely. When I think of a rate of something (like the rate of heat loss or the rate of acceleration), the higher the number, the greater the rate at which something happens (like friction). But no. "Friction Rate", as defined by ACCA, is the measure of the system's ability to overcome friction, not the rate of friction. Look at the numerator: Avaiable Static Pressure x 100. The higher the ASP, the higher the FR. Then check out the chart at 37:19. The FR is a measure of the system's ability to handle pressure drops. So perhaps a better name is NPD (for normalized pressure drop), or DPD (design pressure drop). But there it is. On the latest version of ACCA's duct calculator, you won't find FR. You will find friction loss (in IWC) per 100 feet.
I think one thing you may have overlooked in your analysis and perhaps you left it out because we simply don't know, but it is worth pointing out. The 600fpm rule for branches is based on average desired face velocity for residential rooms for optimal throw. But that is only average rooms under average conditions. So consider this, perhaps these are small rooms under a tremendous load, or more likely this guy is trying to use 1 run for 1 massive room. This means that we will definitely want a higher than normal face velocity at our diffusers to achieve a higher throw. As a side note, yes I am aware that increasing face velocity beyond a certain point has diminishing returns for efficiency and what not, but if this is what we're working with then so be it. This all means that if these are large rooms each wanting just 1 run, than we're going to want a higher face velocity for higher throw, which means we may want a higher branch velocity than 600, which means 900 might not be enough for the main duct. To be fair you can get around this issue, by simply cheating with your branch sizes and making them slightly smaller than you "should" to increase that branch velocity -> face velocity -> throw. Yes you'll sacrifice some efficiency because of this, but at the same time if you don't increase your throw for a large room, you're also still losing efficiency, so you may want to undersize anyway. Again, that's assuming these are large rooms, not small ones under ridiculous loads. But again, this is information, important information, not given to us.
Honestly though a lot of people underestimate, overlook, or don't know or understand the value of face velocity and throw for room efficiency. 600fpm is not a set in stone law, it is a general rule for average residences. This place is not average, and possibly not a residence, so we should definitely consider not sticking to 600fpm here.
thanks for the information, Because where I work they only use rule of thumb for everything and call themselves HVAC professionals but with this information it makes more sense to do the duct work the right way.
Wasn't aware that dut size meant so much for efficencys now I do thank u
Just follow manual D - size most restrictive branch, use that total length. Careful with decimals, we all have a habit of saying one for 0.1 etc… look at any fitting that is sharp edged and find a simpler less restrictive (Less equivalent feet) arrangement for it if possible. Overall good to see you are just not doing the ductulator thing at a .1” or .08”, or whatever is fashionable.
This is standard stuff you learn while getting your State contractors license. I agree on some other stuff can take it or leave it. Always use round with external wrap for best airflow IMO.
When it comes to trunk reduction, it’s helpful to note that the group 2 takeoff effective length are depended on the number of down stream takeoffs to the end of the trunk or a reduction.
That means the 50ft takeoff the sandwell uses can become 100+ without trunk reductions.
Designing my forever home and this info is super helpful in designing and laying out ductwork. Gives me so many things to consider when designing to get maximum efficiency while using minimal space. I would hate to have a 48x36" intake! Lol
Awesome. glad it helped
@@sandwellmechanical since you are up north, have you ever tied in a zero clearance fireplace into a central hvac system? Is it difficult? This would be a new build and designed for this type if integration not an afterthought.
If you're still designing, for the love of God, minimize flex duct. Hardline everything you can.
Thank you for video. Wow… In Canada we rely on engineering drawings, no guess work, professional, scientific approach.. Trades in HVAC must go on a 4 year apprenticeship program, they must attend formal college education, pass certification in order to be a qualified person. Video is good though, much appreciated.
Such a good video, very detailed. Thanks for sharing.
I have some questions:
How do you find the friction factor and pressure loss in duct without knowing the duct material?
What if you dont know the CFM that the equipment´s fan is going to supply?
is it always 1tn=400 cfm?
what about the acceptable air velocity in the ductwork?
Great video, I'm in HVAC school right now, and were going to be getting into ductwork next semester. I was just researching how this works and am really glad I found your channel and this video. Thank You for the time you put into this.
Thanks for watching. Best of luck in school!
@@sandwellmechanical Can I pay you to consult me on skype to design a HVAC plan for our church cafeteria?
I've designed a total of 3 duct systems so certainly no pro. They all moved air quietly and adequately. I would have at least considered turning vanes in some or all hard turns in this example and re-run the numbers. Vanes can make an enormous difference in the effective length.
A. that depends on duct size. B. I believe this is round pipe.
By the way, equivanent length of fittings is not a single number, but dependent on the velocity of air through the fitting. The velocity will affect the pressure drop through the fitting. Higher velocities will result in higher pressure drops and vice versa. Manual D, Appendix 3 explains how this adjustment is made. The "reference pionts" appear to be one of two typs of straight ducts: one have a friction rate of .08 IWC per 100 feet, and another having a FR of .15 IWC per 100 feet. Manual D states "For example, the lenght of a fitting (used in an example in Appendix 3) could vary from less than 1 foot to more than 94 feet (depending on velocity, among other things)". This sounds like a job for a good ductwork design program.
100% correct. I've addressed your exact point in another video a few years ago. Great point though. Thanks for watching
I'm now a fan!! I don't necessarily agree with your opinions about the duct calculators BUT your attention to detail is great! You're going through the Hart and Cooley books!!! I thought only I was this detailed. K.U.D.O.S. To you. NOBODY does this in my area.
Also, and I know this isn't the main focus here but... good beard game.
Thanks for sharing!
I'm sure this is a great video, but I'm short on time today, but will definitely watch all of it at some later date. Don't feel bad that you made an hour+ video. Manual D is complicated and deserves a thorough explanation as you have done here. Thank you! Your example system is one in which the air handler/furnace is on one end of the home and, therefore, there is only one supply trunk duct. So, here is my question: When using Manual D to size ducts, if you have two or more supply trunk ducts off of the plenum, would you use separate friction rates for each one? In other words, would you have more than one critical air path (one for each trunk duct) or just one? Also, I think it's worth noting that, (and this comment isn't just for you, but for everyone reading this) if you think Manual D is very complicated, then you must think sizing gas piping using the longest length method is very complicated, since, if you think about it, this is basically the same methodology. You use only one column for the length and the length column used is the one for the most remote outlet. Same as the critical air path length, right? Thanks again. I really appreciate guys like you who want to do things the right way.
Really this video make me see to all mistake I do with my duct work.
Thanks for the video, very helpful. I was wondering - the .8 of most air handlers (or better - furnaces) refers only to operation during cooling. The ESP of most heating furnaces is .5. So if you size according to cooling, with the furnace be able to operate in the .8 environment. I also like the specs given by Hart and Cooley. The perfect reason not to buy until you can verify the cfm and Ps of a diffuser. It seems so hard to meet the .5 requirement of a furnace in an older house. Thanks, again, Larry
Thanks for the view, and I agree 100%. What I'm hoping for people to take away from this video is just that.. actually looking at the design characteristics of equipment, duct, diffusers, etc shows how difficult if not impossible for "some" of the HVAC installs out there to work efficiently, especially in older homes with limited space, undersized ducts, and newer blowers
@@sandwellmechanical Your video has helped me a lot. After a lot of research, I have learned that in an HVAC system, no one can ask one question (ie what size duct - or what size register in the bedroom) and expect to solve the 10 problems associated with it. Probably better to ask 10 questions and maybe solve one problem. The solutions are as fluid an air. You have helped me understand some terms and considerations. Thank You for the video.
Outstanding training!! I have to ask, are you an HVAC design engineer? I'm guessing your average installer techs no next to nothing about design. Thanks for the great video.
You have to consider all building materials and windows etc
Anyone ever tell you that you kinda look like Rhett from good mythical morning? Great video by the way.
this is so great. manual duct d book in one video 👍🏼👍🏼
obviously the drawing you started with did not have enough information. That said, maybe draw up an example of a 2000 square foot house or office complex, showing room square footage etc. Then design the duct and go thru like the process. I think it would be a big help and even a video to show clients the correct way to design. I agree that all is seen so far is using the 0.1 and no reducers etc.
stay tuned, thanks!
What’s the difference between going off the pressure drop for a certain fitting instead of finding the equivalent length for that fitting?
33:42 - I suppose you could call that an exact guess; since, you were guessing the return size and fittings of his design.
Wow that’s my neighbor howdy neighbor, hope all is well with with you and your family
At 56:44 you said if over 10ft you need to bump that up. The Ductulator is rated for 100ft. How did you know to increase it
He said for flex duct. There are often codes that prohibit flex duct exceeding a certain length. Just because the box has 25' of duct, doesn't mean you should ever run it that far. Installers often do anyway, though. The static friction of flex duct is high because of the way it made. If not installed and supported properly, it has kinks and even higher pressure (and cfm capacity). It should be installed as straight as possible and stretched out so the interior becomes smooth.
Great video. What I’m curious about is how do you source these specific grilles and registers? Does your supply house just carry this infinite number of options for different sizes and restrictions?
Thanks, As far as our local suppliers, no they only have a few options "in stock" at any time, however they can order most of these in if I need an odd ball grille. With that in mind I design most systems with what we have in our stock or is readily available.
Excellent video! Learned a lot.
Glad you enjoyed it!
How were the CFMs for each supply register determined?
This is a good video on Manual D, but there is another very good, more detailed video on UA-cam called 'Duct Design for Great Results by Ed Janowiak'. Ed is a certified ACCA instructor and the current Manager of HVAC Design Education at ACCA.
Good mythical morning.
I assume you have no zones?, seems that duct vents and registers will be opened and closed which would mess up all these calculations. What about variable speed blowers?.
Once you establish a friction rate, how do you know that friction rate is good or bad and adjustments need to be made? You stated yours was too low, what did you base that off of?
Great video! Thumbs up.
I have a question, what do you do if you have CFM left after all your rooms are covered?
I have high static pressure on a new 3.5 ton heat pump. I know for sure the flex duct is the issue. I have two 12" coming out of the supply in opposite directions. I know I need an 18" for a 3.5 ton heat pump. I did a diagram layout of the duct in the attic. What would happen if I just replace the two 12" to 18"?
Ignoring the downstairs, because everything is between the walls. The problem was even worse with an undersized return. The original and only return was a 24x18. The total static pressure on the unit was .9 W.C. I was able to drop the TESP to .66 by making the return 30x24. Since there is so much static pressure and the unit TESP is a .2 and I need an 18" for a 3.5 ton for 1400 CFM. How big does the supply plenum should be and what shape? Should the supply plenum split to 3 18" going out to each of the 3 distribution boxes? Do the other three distribution boxes also need to be larger?
Looking at the triangle shaped supply plenum I have very little room up for a rectangle plenum. I think a 3 feet ductboard supply plenum should work. There is a foot from the Air handler to the ceiling and I think 2 feet from the attic floor to the roof. Now I am looking at two types of designs. Design #1 keeps the 18" ducts straight by having a single 18" coming out of the supply and then a distribution box splitting it to three 18". The sides would be coming out straight to the to side boxes and one going to the third box with a slight curve. Design #2 splits to three right at the supply plenum and goes to each box individually, but all three will have a slight curve. I will not be using any metal plenums..... it will be all flex duct and ductboard boxes, because of budget. I am not trying to make a perfect system, but trying to remove the restriction from the 12" undersized ducts installed and replacing the flex duct that was patched with mastic with new ones.
Another question about the installation..... I have the flex duct running up and strapped to the roof for support. Since the supply plenum is low to the floor due to the roof..... Can the flex duct be run on the attic floor? Can you tell me which layout makes more sense and less restrictive? Thank you.
Layouts:
Current
i.ibb.co/Ld9kmPM/Flex-Duct-Layout-and-Size.jpg
Option #1
i.ibb.co/GHyS00g/2022-07-05-0002.jpg
Option #2
i.ibb.co/PNN8mSB/2022-07-05-0001.jpg
Air Handler Specs
ibb.co/17VvF4B
Video of attic
ua-cam.com/video/iInIN89q8GU/v-deo.html
U may know what are taking about.u need a print of house lay out.
This guy may know his stuff but he has no idea how to express it in a cogent manner. Too bad. Why is he working with faulty or incomplete information? We all should appreciate those really good teachers we had after suffering through this.
What would you have done differently?
@@michaelwestmoreland2530 I am just a retired guy trying to learn. My point is that although he appears to be quite knowledgeable, he is not a good teacher. Teaching is a special skill that he clearly doesn't excel at. I assume that most people have known a few exceptional teachers over the course of their lives so they would understand my point. I know that I have and what made them exceptional was that they were easy to understand and follow and made learning easy. Perhaps my assumption is incorrect. That's all I meant.
Learned more here than 2 years at college in regard to ductwork
@@anthonygulla3055 "I don't understand the material, therefore the individual is a poor teacher." Fallacy. This is a video for pros who know the basics. Are you retired from the HVAC trade? If not, this is like teaching algebra to a 3rd grader. No teacher in the world can teach a 3rd grader the concept of a quadratic equation and the formula that goes with it, or the concept of a square root having +/- values that need to be accounted for. 🤷🏻♂️
After watching this video, I went out and bought some of the manuals esp D and he is taking this straight from the book, just how he understands it. Not word for word but the general way of correctly sizing. No he didnt use by the book exact figures, but the steps are right. I was able to read the manual D and know exactly what he was saying. Good vid
So, I'm not really sure you need to subtract the evap. coil on an AHU for the TESP. I have read that is included with the AHU specs, and it's only a factor when using a furnace with an external coil?
That is correct Thanks for watching
Thanks for the question and answer. I was just thinking about this today!
Great content. Very refreshing to see someone that takes there trade seriously.
I have a question on my own system. I have a Goodman unit in my house and the spec sheet shows 1200 cfm at .5 ESP. In your example you didn’t talk about static pressure vs cfm. Do I just use .5 as my blower rating in the formula?
Yes, you got it!
@@sandwellmechanical
Ok so I did my calculations and similar to your example my available pressure is too low. I believe my only option is to change my blower motor to a higher rating. My unit is a Goodman 2 stage high efficiency with a variable speed blower. Do you know if I am able to upgrade that to a blower with a higher ESP?
Very loaded question lol. But YES and NO.
Obviously we would need to know a bit more of what you've got, however, I will assume you are running an ECM motor as it is a 2 stage furnace. Now this is where the residential/ light comm divisions are lacking. As opposed to our large equipment, we are stuck with what the factory has available. Now that's not to say we can not physically remove the original motor and bump it up a size, bc that you certainly can do. I would say though to take a look at the hp of yours vs the next size static/cfm ratings. I wouldn't be afraid to use 0.6-0.8 in my calculations for the ductwork in your application if you are borderline able to make this work. Now keep in mind with ECM blowers I need that static used in the calculations as low as possible, as you will find how expensive it gets running these against high pressure... And on the other hand, if you use a 0.8" and still not making the calculations come together, unfortunately it's back to the drawing board with the duct work.
@@sandwellmechanical
Thank you for the reply. Your assumption is correct. 2 stage heat with ecm blower. Based on what I learned from your video I will have the restriction of the coil at around .25 and the restriction of the filter around .2. That basically uses up the available pressure of the original blower right there. I assume because the unit was only for heat the blower is very weak.
So if I contact a Goodman dealer will they help me upgrade the blower or do I need to figure it out by myself by looking at the specs of other units?
Do you offer a service to help with system design? I would gladly pay you to help with design. I am having trouble finding someone local.
Add a split unit
Awesome video, definitely will be referencing this in the future.. What velocity do you shoot for with metal duct?
I could answer that with 4 different figures depending on size, application, and design. but for sake of simplicity id shoot for 750 in residential
I like your explanation but when it comes to heating and cooling some things don't make sense. Nowdays they design the supply vents to be under outside windows. With houses now days many outside windows are 60" tall. The first thing people do it put floor length drapes on the windows. In winter at night they close the drapes and cover the supply register that you took all that time to calculate the flow and size only to be covered by drapes. Why? I can see them being on the outside wall but why would they put them where they know they will be covered?
You supply air where the load is. That is the same reason radiators were located under windows. With double and triple paned windows, the load is much less, but it is still the place where some of the highest envelope loads occur. If you take care of the load at that point, the rest of the interior is more comfortable.
do multiple return filters and spread them arond. Why not use 4" filters in return boxes? Why does the industry make that one so tough?
lol no returns on the og print. sales guy is a savage
for a 3 floor 7000 sq feet (total) residential construction with Daiken VRV would you go with duct or ductless?
The furthest register from the unit is key.
I do not work in the HVAC industry, but I am curious. Question: do you use the same friction factor for sizing the return duct, the same as used in the supply calculations? If the answer is YES, then basic rules of thumb I read/heard about: 0.1friction factor for supply and 0.05 for return would be way off since they are different between supply and return, instead of being the same. A difference in the friction factor between supply and return would only be justified if we would want a different air speed for the return, different from the say 750ft/min design speed of the supply main.
You use only one friction rate for both the supply and return ducts. The reason for this is that the critical air path is calculated by measuring the supply and return ducts lengths, then adding the total effective length of all of the fittings (like register boots, return air drops, adjustable elbows etc) to the measured length. This gives you the TEL (total effective length) of a register run. The register run (which runs from the return air opening after the return air grille to the air handler or furnace, then from the supply plenum that is attached to the top of the furnace/air handler through the supply trunk duct to the register branch duct through the register boot) with the largest TEL is called the critical airway path . If you can supply the required amount of air (CFM) to the register in the critical airway path, then you automatically will supply MORE than enough air to all the other registers; To keep from supplying too much air to all the other registers, you install volume dampers in the register branches and adjust them until you get the required amount (CFM) coming out of the register (you need to use an air balancing hood to do this). Once all of the dampers have been correctly set, then each register run will have very close to the same amount of resistance to airflow as the register run that is in the critical airway path. Thus, all of the register runs will offer nearly the same amount of resistance (friction) to airflow, and that is why the Manual D duct sizing methodology is also known as the Equal Friction Method of sizing duct.
Great video, but you lost all credibility by using ductboard!😁
ductboard and flex!!
@@sandwellmechanical "the right way"
Thanks for the video - I followed along up until about 37 minutes in - not sure what the ideal number would be. Is 0.071 good or bad for most homes? Also - slide rule? Is there no decent online calculator? I undertand they want to sell these things, just surprised there isn't an electronic alternative. Also is 900 FPM what you usually want to aim for?
I find that something around 0.07 on the supply is common, however we often use much lower as well. I have not come across an online calculator for this, but that's not to say one doesn't exist. As far as the electronic alternative.. I use one almost everyday at work, I seldom use the actual ductulator much anymore
Please don't skimp on duct size for cost. Use the Equal Friction method, velocities based on type of system you'll be OK. Avoid duct board, high aspect ratio square duct and long runs of flex. Think performance. It's possible to exceed 400CFM / ton with the correct air distribution design and installation. Many installers / contractor's under size the return air filter system. Big mistake. Don't forget to test / air balance.
If your sensible to latent ratio is very high, then you may be able to have a bit higher cfm/ton, but humid climates will often require lower than 400cfm/ton.
Good video
As a technician now I better understand why I would into systems with airflow issues with poor duct design
Thanks for watching
Yo Sandwell buddy just makin sure now, the friction rate is on each manual of the air handler depending on the speed of the blower? And we have to match that friction rate based on how we calculate sp, pressure drop, equivalent length, etc after the design is complete correct?
yes sir, you got it. Ill have shorter videos coming soon as ive had a lot of questions regarding this video. Thanks
I know this is dated, but is it worth installing a 24” coil above a 100000 btu variable speed 21” gas furnace in order the save .10 to .12 w.c.? My variable speed furnace is rated at .10 to .80 w.c. Thanks for a great video!
If you have the means to transition a 24" coil to a 21" furnace cabinet, absolutely. Especially considering your furnace is running an ECM blower. Keeping the pressures as low as possible is key to making that motor last. Thanks for watching!
@@sandwellmechanical Thanks, I have enough height in my utility closet, but I’ll have to shorten my 19” round supply duct leaving the coil by 6”. I’ve sourced a SST-CD-R6 21 to s4 coil box that should work well. Your information and help are greatly appreciated!
Question. Due to California SJAQCD where I live, I will need to down size from a 110000 btu 80% afue to an 80,000 BTU Ultra Low Nox unit single stage burner/variable speed blower 96% AFUE. I’ll be 11,200 BTU short from my current 28 year old unit. I’m not too concerned, but wonder if you gave an opinion on that. I could go to and 80 AFUE 100000 btu but it’s single stage and single blower.
Sorry to hear about your local restrictions. Now, this is a very loaded question which immediately triggers a bunch of questions on my end. Such as loads of building, physical size constraints, AC size, and so on. Long story short if you 'truly' can get away with the downsize of furnace thats fine. My concern however is not heating for you, its cooling cfm requirements, as I assume you are in Southern CA.
It could be a open attic rerun for a restaurant
that math doesn't seem to add up, don't you add the restrictions? since they are all added as restrictions? so .8 and .2 gives a 1.0 of resistance? subtracting them is actually removing them from your equation? I'm sure I'm wrong but that's my train of thought.
Question please. When doing the ASP = ESP - DPL, do I include all the home's registers in the DPL? Have 11 of the them. By the time I do the FR = ASP x 100 / TEL, I will have a negative value! Cheers, Grant
no only count 1. The 1 on the critical/ longest path
Thanks for your reply. Very helpful. Love your engineering videos and sarcasm. You remind me of my old engineering teacher (not HVAC). One day he said to us young guys, "If you don't want to do this stuff right. You might like to remove yourself from my glass and find a job selling tennis rackets". I think it was one of those guys that did the duct work in my attic that I am redoing from scratch. My furnace is horizontal with with 10' of return from a wall mounted grill and filter to the "top side" of the blower box. I am going to add a mirror image of this return line to the "bottom side". Will I include both grills and filters or just one of each to the DPL? Thanks again for your help. Grant
Nice video. What is the alternative of duct calculator?
computer software!! or mathematically figuring each section based on cross sectional volume and friction loss coefficients per material used. Then shooting for a specific velocity based on the system criteria. We certainly can do it without one, but its just the time involved.
Care to size my basement remodel's supply and return? If so let me know!
I do them often. john@sandwellmechanical.com
Great stuff
Question: When someone says, “This size duct, or boot, or whatever it may be will deliver a certain amount of CFM.”..... is it just assumed that they’re implying a velocity of 600 FPM for residential, or a certain FPM value. I’ve only been studying ductwork for a few months, but from what I understand size AND velocity equals CFM..... Seems like there’s something I’m missing. Thanks.
You are on the right track. all too often, wholesalers, retailers, and even contractors/ designers, will used a presumed velocity (600-900fpm) for general sizing. 6" - 100 cfm, 400cfm per ton and so on...
@@sandwellmechanical Thanks for the reply! I'm learning what I don't know to figure out what I need to learn. Lol.
Their are computer programs that do this automatically in second's ( manual J). The good one's will even tell you how many hanger's screw's etc, it will take to do the job. He never accounted for insulation value, window's etc.
Manual j is heat load calc, this video is on duct design which is manual d.
Work
Where did you get the Cfm rating tho
Has anyone ever told you that you look a lot like a young Mathew McConaughey.
Should I get bryant with flex duct or mistubishi ceiling casstes
Depends on the building layout. We will try to utilize a conventional ducted system as often as possible. BUT, there are several times were we will need to use ductless systems due to layout criteria. I have another video showcasing the pitfalls of using "flexduct" excessively
My head hurts
Thanks for the video however you can improve by preparing your materials in advance instead of on the fly, This way you can focus on the points you want to make. You should have been able to cover the material i less than 60 minutes.
Link me to your video please.
Most houses I have seen seam to be starved for cold air return
Your filter grill should be 300 fpm or less 🤔
Well.. at least I'm not the only one out there, who is a little crazy about design. Too bad- ppl won't pay for the job done right 🤣 and hire neighbors to save money. At least it keeps me busy with x13 ecm replacements.
37:31...The acca wedge...I see
I don’t doubt you know every damn thing you’re talking about but you should have started with the basics of duck work. you started at level five, most guys are at level one trying to figure out how to get started
good point, Thanks
This guy is eating his nail when he is in hunger.
Ilove ductman😍
I will never calculate a job i can not see OR a set of prints.
agree 100%
7:25
YOU STARTED OFF STRONG THEN IT GOT A LITTLE WILD LOL ( I KNOW ITS CUZ OF STRANGE CFM DAMAND) IT WOULD BE NICE TO SEE A REAL JOB THAT YOU ARE INSTALLING
I assume this video has a ton of useful information, but because you didn't bother to show how to find your start point, i.e. how do I decide how big a unit I need, how do I decide how much cfm each room needs, what size furnace to buy, and instead your whole premise for the video is a small sketch that you point out is missing pertinent information, this video is useless to me.
this video, I had to give up watching it. so much repeating, so much saying you don't know this length and that - YEA, we get it - 15 mins in and all I know is you have to add your lengths.
Nope.
This is system design.
It's not duct design. AHU coil dp, for instance, is entirely irrelevant to the size of the duct. It's the air in and out that matters (pressure and volume/time). The kind of equipment is irrelevant to the size of the duct as well. This video is fundamentally wrong because it conflates system design with duct sizing.
Amigo why not making this more simple... Everything was going well untill you starting adding and subtracting. I think peopke will understand if you make the video very simple
Granted it’s nice to do all that but today there are hundreds of programs that will do this for you, and from what I’ve seen in the real world… rules of thumb do work but only when they are followed correctly, and when all is said and done, they both are of no real significance. Doing all the calculations take a significant amount of time and effort. And the customers don’t want to pay for that, so you had better be able to pop this out lickity split.
All over the place, maybe make your game plan prior to making a video.
This is what happens when you have no religion or hobbies in your life
Yes, stand by for my church design video we are doing now
@@sandwellmechanical only joking because of how ridiculous and mundane hvac calculations can get
This video is terrible. Duct design isn’t that hard, or hard to teach if you have all the proper information. You shouldn’t even start if you don’t have all info. ACCA has a course, pay the money and learn right.
The duct design may not be terribly difficult, but there are lots of things to consider; fabrication, noise, pathways in the building, conflicts with other trades (try running down a hallway in a hospital) and many other considerations. He has already tried to make it pretty simple. And of course you need to know how to properly do heating and cooling load calculations, properly the equipment and distribution devices and system layout. For instance, you can really screw-up a system design by improperly placing thermostats. And balancing a system after installation is also a critical step that is too often skipped. I am a professional mechanical engineer and have designed thousands of systems since I started back in the early '80s. Too many people do everything by rules of thumb. Rules of thumb are great to see if you are in the right ballpark, but they are not a design. Unfortunately, the HVAC design in most homes is just an educated guess. Even if the model design was done properly, when you change the orientation or location, you change the load design.
Horrible backgound music 🤮