Originally Posted by nholmes8669
The blower is a 3 speed blower and is set at the highest setting. I am unsure of the cfm's at each speed. It is a comfortmaker 75,000 btu furnace 80%. There is no return air duct on the 2nd level but I plan on adding one when I add a bathroom up there in the next couple months. The rest of the ducts throughout the house are 6" round. It is an older house and all the return air runs on the first floor used the floor joists as ducts.
You have not give enough info to even begin to do any engineering. Like SQ' of lower story, SQ' of upper story Sizing of all the return air ducts, size of all the
supply air ducts. They make 75,000 btu furnaces with 2 ton, 3 ton, and 4 ton blowers A 2 ton blower is max. 800 CFM, a 3ton is 1200 CFM, a4 ton is 1600 CFM. If you give me all the numbers off the furnace than maybe i can tell which
blower you have. One thing you can test is take off the blower door tape the door switch so it will make contact. Now start the furnace and with the blower running check the air flow up stairs with door off and with door on. If you get a lot more air flow with door off than your return air ducting is not large enough. Of course if you put so much CFM. up stairs you have to take that much return from up stairs. later paul