Furnaces have a BTU's input rating, for simplicity lets say 100,000 BTU's and it is a 95% furnace, then we multiply the 100,000 BTU's X 0.95 and get 95,000 BTU's output. If you measure the BTU's after finding how much air the unit is moving and multiplying that by 1.08 X Temp rise between the supply and return it should come out close to what it is rated for.
@@shggydg9100 Not usually, most furnaces use a different fan speed when you set the thermostat to FAN. Same holds true for heating and cooling. We want to set the fan speed in heating to the proper temperature rise. This temperature range is printed on the manufacturer label inside the furnace. The one in the video is 35 to 65 degree temp rise. So I would measure the difference between the return and the supply and shoot for a temperature rise of 50 degrees, smackdab in the middle of 35 to 65 (15 degreesis right in between those two numbers add 15 degrees to 35 for targetof 50). If the temperature is higher than 50 switch to a higher fan speed and if lower switch to a slower fan speed. For cooling we want 400 cfm per ton. The National Comfort Institute NCI, has a different method to determine the correct temperature rise. They calculate temperature rise based on the efficiency of the furnace. A 70% furnace they divide the furnace btu's by 10,000 and multiply that number by a constant of 100 for the cfm, example a 100,000 btu's furnace is 100,000 ÷ 10,000 = 10 × 1000 = 1,000 cfm. For a 80% furnace the constant is 130 and 90% furnace the constant is 150. The only other step is measuring the amount of air the system is producing. The class that teaches this method can be taken at various locations in California for free through the TECH program. Visit the NCI website for details.
great job
Thank you this will help me out in the field
Your welcome
I would have been interested in seeing how putting the blower on medium would have played out.
Question: If you had a 90% Furnace would you had to multiply 45,000 x .90 ?
Or where did you get the .80 from?
Thanks, I loved your video!!
Furnaces have a BTU's input rating, for simplicity lets say 100,000 BTU's and it is a 95% furnace, then we multiply the 100,000 BTU's X 0.95 and get 95,000 BTU's output. If you measure the BTU's after finding how much air the unit is moving and multiplying that by 1.08 X Temp rise between the supply and return it should come out close to what it is rated for.
Can fan only mode be used instead of firing up furnace or ac?
@@shggydg9100 Not usually, most furnaces use a different fan speed when you set the thermostat to FAN. Same holds true for heating and cooling. We want to set the fan speed in heating to the proper temperature rise. This temperature range is printed on the manufacturer label inside the furnace. The one in the video is 35 to 65 degree temp rise. So I would measure the difference between the return and the supply and shoot for a temperature rise of 50 degrees, smackdab in the middle of 35 to 65 (15 degreesis right in between those two numbers add 15 degrees to 35 for targetof 50). If the temperature is higher than 50 switch to a higher fan speed and if lower switch to a slower fan speed.
For cooling we want 400 cfm per ton.
The National Comfort Institute NCI, has a different method to determine the correct temperature rise. They calculate temperature rise based on the efficiency of the furnace. A 70% furnace they divide the furnace btu's by 10,000 and multiply that number by a constant of 100 for the cfm, example a 100,000 btu's furnace is 100,000 ÷ 10,000 = 10 × 1000 = 1,000 cfm. For a 80% furnace the constant is 130 and 90% furnace the constant is 150. The only other step is measuring the amount of air the system is producing. The class that teaches this method can be taken at various locations in California for free through the TECH program. Visit the NCI website for details.
I m confused with the btu when you entered 658 on the app. How do you do the math when you get the cfm?
How is this system 82% vs 80%