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second floor won't cool down

Posted by suzan30 (My Page) on
Fri, Jun 29, 12 at 11:51

I purchased my home two years ago. The AC is older but still functioning well. I have it serviced every year. This summer I've noticed that there is an extreme difference between the first and second floor. To got the 2nd floor cool enough for comfort, the temperature ha to be set very low (72 or so) and then the first floor is freezing. Last year, things seemed fine. Any suggestions?

Follow-Up Postings:

RE: second floor won't cool down

Second floor always hard to cool because heat rises. But same house, same AC should not be different one year from the other. Did you change anything ? close or open any of the air registers ? The only thing you can do is try to close some of the downstair registers and force the air go upstair. (but don't close too many/much which will damage your AC itself.)

RE: second floor won't cool down

Typical summer AC problem for two stories operating off one system.

Unfortunately, there is not a down and dirty answer to your question.

Do you know if you have separate returns on both floors?

How's your attic insulation? How are your windows?

Do you know if you have manual damper control on the supply trunk lines to each floor? If you don't know, you need to find out.

Unless. You are having some mechanical problem with your system, I doubt if anything is amiss. You may just be noticing the problem especially if you are having high temps.

I would get a cheap digital thermometer so you can take readings of your supply vents at different locations upstairs and at different times of day.

Of course, your ductwork system in attic should be checked for any leaks.


RE: second floor won't cool down

I think closing registers is a poor choice. Yes adjust dampers on the trunk lines but not room registers.


RE: second floor won't cool down

Thanks for the follow up. I just checked the temperature on each floor. Thermostat is set at 72 and thermometer reads 72 on the first floor, upstairs it is 80(!!!) and in the basement, it is 68. I understand that the 2nd floor will be warmer, but isn't 8 degrees a bit extreme? I can close the vents in the basement which is always too cool when the AC is on.

I don't know about the returns (separate or not), but my windows are old and in need of replacement. There is no attic here. How do I know how the returns work?

RE: second floor won't cool down


Do you think there's really a big difference between adjusting a damper vs a room register? Please explain.

In cases where there's no damper and one room (often close to the source) is blowing too hard, what do you suggest be done?

Sorry for the mini-thread hijack.

RE: second floor won't cool down

Check your ducts. Something might have become unhooked.

I'd say that closing dampers is better than closing registers for at least one reason. Ducts leak so the less duct you have pressurized, the less leakage you will have. If the ducts are outside of the house envelope this is a much bigger problem than if the ducts are inside the house,

RE: second floor won't cool down

shutting the air flow off at the supply grill
doesn't put the air back into
the supply plenum to be redistributed throughout
the house.
it simply stops it from exiting the duct.
the full force is still in the duct. by not allowing
it to exit, you can increase the static pressure
of the duct system.

manual dampers are best located at the plenum.
the duct is connected to a duct take off or collar.
the take offs either have manual dampers or they
you can install them by replacing take off with a
dampered take off. but then you have to be sure
to reseal (with mastic) the take off to the plenum,
set the damper, and reattach the duct..and mastic seal.
bring insulation to plenum so that no metal of take
off is exposed.
I usually put a piece of mastic tape
at the damper on the bottom of theduct take off
to keep it from viberating. if it viberates it will
change the position of the damper over time.
mark on plenum which direction to
move damper to close.

if ducts leak..they leak at any pressure. mastic
seal of ductwork is always a good thing. as is sealing supply boxes where they penetrate into
conditioned space. I use mastic tape..see attached
picture to seal from inside house.

best of luck.

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