Air conditioner doesn't work right. Upstairs 15 degrees warmer than down. HVAC company says...beats them.

Question

30 year old house. Airconditioner is relative new and strong...plenty big for this size house. Older weaker unit used to cool upstairs fine. Vents and returns are in proper positions. Air handler in basement is blowing strong. Filters are clean and new.

HVAC company tested coolness in vents in basement...the duct leading to the first floor was seven degrees cooler than the one inches away that leads to the second floor. I know that upstairs is harder to cool...but when you start off with a 7 degree difference in the basement...and add to that the warmth naturally upstairs...it makes things unbearable. We have an attic fan....ceiling fans....and multiple stand alone fans upstairs. HVAC company essentially gave up. Any suggestions? Thanks.

Answer 1

Gotta go with the last two answers. If the older weaker unit used to cool with no problem, then something about the new one is not right. Improper sized duct sounds like it is the problem. It may mean a new trunk line needs to be run to the upstairs.

Get with the company who installed it. If they can't do it, find some one who can figure the proper size

Answer 2

You say, "older weaker unit used to cool upstairs fine".  

It sounds as though it is not fine, if it is giving you air that is 7 degrees warmer than the air from the newer downstairs unit.

I may be misunderstanding what you are saying...because HVAC company would suggest you replace the older unit for upstairs as that seems to be the problem...they wouldn't just give up.

So assuming you don't want to replace the unit for the upstairs, your best option is most likely to get a portable A/C unit for the upstairs. or window unit.  I have a portable one that costs about 400 bucks.  It is a heater/AC/dehumidifier all in one.  It is a bit loud and you have to vent it to the outside and empty water bucket often. (or find a way to put the drain hose into a house drain)  But it does blow ice cold air.  At the time I needed this unit, I valued the cold air more than I did the inconviences of the unit.

Your other option is to paint the walls with Ceramic Paint, make sure windows are sealed and block the radiant heat with Tint, etc..   Plus you may need to check the insulation in the attic and update it.

I have painted several rooms in my house using a ceramic additive I got from Hy-tech ceramics.  Those rooms are much cooler than the rooms I have yet to coat.

Good luck.

I provided a link for the ceramic additive, but I am not trying to sell it you...it is simply something that worked for me.

Answer 3

Your ductwork was origionally set up for your "old weaker" unit. Your new unit is most likely moving more air than the older unit and your ductwork may not be sized properly now.

This should have been addressed when your HVAC company estimated the cost of a new unit.

Sounds like your HVAC company isn't up to speed on ACCA guidelines. Was a complete Manual J heat load calculation performed by your HVAC company? I highly doubt it by what you have written.

Anyway, the cheapest route would be to install dampers in the duct leading to the 1st floor and the 2nd floor and reduce the flow of air to the 1st floor and try to force more to the second. ALthough, this won't help much if the ductwork won't handle the amount of air that is being fed to it.

The way to actually fix your problem is to have a complete Manual J calculation performed, followed by equipment selection from Manual S, and duct design according to Manual D.

You have to decide what you want for your new unit. Is the old ductwork going to kill that pretty machine you just paid for? Maybe. If your airflow isn't correct, you will loose your compressor.

Sounds like a long road ahead for you.

Answer 4

What about adding a fan to the duct work upstairs so it will draw the cool air up above the upstairs rooms. Cold air is heavier then hot air and with the funace in the basement you need a real good fan to push those cfm's that's why they are finding that A/C Units work easier in attic locations, but the other downside is water draining from the unit. I have seen a few that caused some big water damage cause the over follow wasn't installed right. But I would try to add some duct fans and see if they can be set up to a T-stat so that when the upper rooms reach a set temp the fans will kick in to make up the difference by drawing the cool air up to the top floor, the other thing is to check the return air follow from upstairs if the furance isn't pulling the room air from the upper rooms you can't force more air into the space. So maybe if you check into these it might help Good luck

Answer 5

Oversized equipment, short run time where old unit ran longer and kept the air mixing and circulating.

Poor duct sizing for the new unit.

Keep after the contractor until this is resolved. When you take short cuts and hack in a job, it should come back to haunt you!

Answer 6

it must be how your house is insulated.

Answer 7

Close a couple of vents down stairs. Not completely and force more air up stairs and see if that makes a difference

Answer 8

Sometimes restricters are added to duct beneath the house, possibly you have one of these and could have been covered with insulation, therefor unnoticed.