It is the most common comfort complaint we hear in Houston: the downstairs is fine, the thermostat says 74, and the upstairs bedrooms are unusable from about two in the afternoon until well after dark. The air conditioner is running. It just is not winning up there.
This is not usually an air conditioner problem. It is a building problem, and it has a small number of specific causes.
Why heat concentrates upstairs
Heat rises, and it arrives from above
Two things work against your second floor at once. Warm air inside the house naturally moves upward, and the attic above is running at 130 to 150 degrees and radiating down through the ceiling. The upstairs is squeezed between both.
The ducts serving upstairs are the longest run
In most two story Houston homes the air handler is in the attic and the upstairs supply runs are the ones snaking through the hottest part of that space. Air that starts at 55 degrees at the coil can arrive noticeably warmer at the furthest bedroom register, and the rooms at the end of the run suffer most.
Duct leakage makes it worse
Residential duct systems commonly leak at the connections. Every leak on the supply side is conditioned air delivered to the attic instead of your bedroom. Every leak on the return side pulls 140 degree attic air into the system, which the coil then has to cool again.
Bonus rooms over the garage are the worst case
A room over a garage has an unconditioned space below, attic above, and often three exterior walls. It is exposed on more sides than any other room in the house. If your game room is the problem room, this is why.
Things people try that do not fix it
- Closing downstairs vents. This raises static pressure in the duct system and can make delivery worse overall, not better.
- Turning the thermostat down. The system runs longer, the downstairs gets cold, the upstairs still does not catch up, and the bill climbs.
- Adding more attic ventilation. More outside air moving through a 140 degree attic in a humid climate does not solve heat gain through the ceiling, and can pull conditioned air out of the house through ceiling leaks.
- A bigger air conditioner. Oversized equipment short cycles, removes less humidity, and still fights the same heat gain.
What actually works
Move the attic inside the conditioned envelope
Spraying foam at the underside of the roof deck and sealing the vents turns the attic from a 140 degree oven into a space close to house temperature. Your ducts are no longer running through heat, the ceiling is no longer radiating down into the bedrooms, and the upstairs stops being a different climate zone. This is the single most effective fix for this specific complaint, and it is covered on our attic insulation page.
Seal the ceiling plane properly
If your ducts are not in the attic, air sealing the ceiling and adding depth may get you most of the way for less money. The air sealing is the part that matters, and it is the part usually skipped.
Insulate the walls of the problem room
For bonus rooms and rooms with multiple exterior walls, sealing the walls with closed cell foam addresses the sides that the attic work does not reach.
Have the ducts checked
Sealing and, where needed, resizing the runs to the far rooms is HVAC work rather than ours, but it belongs in the conversation. We will say so when we see it.
How to work out which one you need
Three questions get you most of the way. Where does your ductwork run? What condition is the existing attic insulation in? Is the problem room exposed on more than one side? A free inspection answers all three, with photographs, before anyone quotes you anything.
Frequently asked questions
Will a second AC zone fix my upstairs?
Zoning gives you better control, but it does not reduce the heat coming in. If the attic is still 140 degrees and the ducts still run through it, you are managing the symptom at a fairly high cost.
Is an attic fan a good idea?
Powered attic fans can depressurize the attic and pull conditioned air up through gaps in your ceiling, which means paying to cool the attic. In a humid climate they also draw moist outside air in. We generally do not recommend them.
How quickly would I notice a difference?
Immediately, in the sense that the attic temperature drops as soon as the work is done. Most clients report the upstairs feeling like part of the same house within the first afternoon.
Do I have to seal the whole attic, or can I do part?
It has to be complete. Sealing some vents and leaving others creates air movement through the assembly with nowhere controlled to go, which is worse than leaving it alone.
Get the upstairs looked at
Call (346) 775-9128 or request a free estimate and we will tell you which of these is happening in your house.