r/hvacadvice Jul 31 '21

Questions on improving my AC. I have one unit and two floors, large 8+ degree difference between the two floors..

Hi guys,I have a 2500 sq ft house, with two issues that I'm trying to address.

The core of the issue is I have one single AC unit, and one thermostat (downstairs).

My downstairs is pretty much one large open plan area 3/4 the size of the upstairs.

That's because my garage is directly under my master bedroom. Imagine a square with four quarters, my garage is one of those quarters, and up stairs we have a room in each quarter.

So because my garage, which is in Houston, gets like 100+ during the day (no AC to garage), my master bedroom becomes the hottest room in the house..

I wasn't sure why, but it's a combination of that side of the house having no tree shade, and the heat in the garage has to radiate upwards, into that master bedroom.

Combined with the obvious heat coming from the roof above, my upstairs is roastie toastie.

As mentioned I have one thermostat downstairs.

The core of the issue is:

If downstairs is at a reasonable temp (75-77), up stairs is like ~85.

Which if you try to go to bed or even have a shower it feels hot as bolas.

If I set my AC downstairs to a temp to pull upstairs down to ~~77.. I have to set my downstairs to like 68.

The downside this is, during the hot summer it means my AC is running pretty much 24/7.

I did it for one month, and my electricity bill went from $130 to $350.

I have been doing some research and seems I could use dampers?

I think if add a second thermostat upstairs and it would control the dampers that would restrict flow downstairs to equalize the temps.

Is this correct?

My AC vents have grills on then that can also restrict flow, and I closed then by about 1/3 and it def moved the temps on the two floors closer to equilibrium.

Someone told me I should never touch the vents on the ceiling and they should be 100% open all the time?

If so, why are they there?

What's the difference between me manually closing the vent slightly, and using a damper in the ducting to essentially do the same thing.

Is this my only option?

Short of installing another unit to control upstairs (large expense) I think this is all I can do?



u/zacce Jul 31 '21

Someone told me I should never touch the vents on the ceiling and they should be 100% open all the time?

This topic is controversial in this sub. Some agree and advise never to touch vent. Others say it's okay to adjust (but not 100% close).

My take is the latter, as long as no icing.


u/Weak_Relative_7767 Jul 31 '21

How big is the unit and is it zoned? Is it sized properly to the square footage of your house and codes?


u/Tea-Money Jul 31 '21

You could try the flair smart vents. That would close the downstairs vents when it’s satisfied & keep cooling upstairs.