Hvac question

cmartin · 08-27-2014, 06:36 PM

We bought a 2 story house and the vents are in the floor (slab)on the lower level and in the ceiling of the upstairs. Down stairs cools great but the vents upstairs seem to hardly blow. We have closed some of the vents downstairs to try to get some more air up there. The furnace is on the first story

What are my options???

tbshakie · 08-27-2014, 11:41 PM

Not an HVAC guy, but I dealt with this before. Run the furnace fan 24/7. helps a little..... Then add a booster blower to 1 or 2 of the ducts running upstairs. I did this at my house. 1 booster made a huge difference. Tried it on the other side of the house and it didn't work because it sucked too much air away from the first one.

I will bet good money that you don't have enough return air on the second floor. I didn't. a 3.5 ton A/C system (what I have) needs ~1,400 cf of air. I had 700 cf. What size air conditioner do you have? take 400 cf per ton of air. get that number. now count your return vents, each return in a 16 inch on center wall (non metal but using the wall cavity) equals 100 cf.

Example: My house: so for a 3.5 ton system needs 1,400 cf of air. counted my air returns=6 (5 singles and a bigger one that took up 2 stud widths). 700 cf of return air. no wonder my upstairs was so freaking hot in the summer and cold in the winter. NO CIRCULATION.

Next. take your returns off and look down (or up) with a light. did the cut the sill plate out fully? Not in my case. the SOB builder 1/2 assed it and left a small opening. I didn't event have 700 cf of return.

so what did I do? Dropped out the whole truck line in the basement, used an electric chain saw to cut out the sill plates, ran 2 more returns (one on first floor, one on second floor), one more air supply up stairs. still wasn't enough. I added on to a wall downstairs and ran a huge floor return to the large room upstairs. that did the trick.

They also say that installing a furnace (and A/C unit that is 2 stage) with a variable speed blower helps too, but I couldn't afford it at the time.

Again- NOT an HVAC guy. But I got fed up and went through this before. Ripped up the upstairs floor to do it. But the proof is in the pudding.

08-27-2014, 06:36 PM	#1
cmartin Join Date: Feb 2011 Location: miamisburg Posts: 191	Hvac question We bought a 2 story house and the vents are in the floor (slab)on the lower level and in the ceiling of the upstairs. Down stairs cools great but the vents upstairs seem to hardly blow. We have closed some of the vents downstairs to try to get some more air up there. The furnace is on the first story What are my options???

08-27-2014, 11:41 PM	#2
tbshakie Join Date: Apr 2012 Location: Circleville Ohio Posts: 61	Not an HVAC guy, but I dealt with this before. Run the furnace fan 24/7. helps a little..... Then add a booster blower to 1 or 2 of the ducts running upstairs. I did this at my house. 1 booster made a huge difference. Tried it on the other side of the house and it didn't work because it sucked too much air away from the first one. I will bet good money that you don't have enough return air on the second floor. I didn't. a 3.5 ton A/C system (what I have) needs ~1,400 cf of air. I had 700 cf. What size air conditioner do you have? take 400 cf per ton of air. get that number. now count your return vents, each return in a 16 inch on center wall (non metal but using the wall cavity) equals 100 cf. Example: My house: so for a 3.5 ton system needs 1,400 cf of air. counted my air returns=6 (5 singles and a bigger one that took up 2 stud widths). 700 cf of return air. no wonder my upstairs was so freaking hot in the summer and cold in the winter. NO CIRCULATION. Next. take your returns off and look down (or up) with a light. did the cut the sill plate out fully? Not in my case. the SOB builder 1/2 assed it and left a small opening. I didn't event have 700 cf of return. so what did I do? Dropped out the whole truck line in the basement, used an electric chain saw to cut out the sill plates, ran 2 more returns (one on first floor, one on second floor), one more air supply up stairs. still wasn't enough. I added on to a wall downstairs and ran a huge floor return to the large room upstairs. that did the trick. They also say that installing a furnace (and A/C unit that is 2 stage) with a variable speed blower helps too, but I couldn't afford it at the time. Again- NOT an HVAC guy. But I got fed up and went through this before. Ripped up the upstairs floor to do it. But the proof is in the pudding. __________________ 1976 CJ 5 1984 CJ 7 1993 K3500 GMC 6.5 TD