Short answer
Close the blinds on sunny upstairs windows. Open the upstairs vents all the way and close the downstairs ones about halfway, never fully, to push more air up. Keep upstairs doors open and return grilles clear, set the fan to "On" for a few hours to mix the air and replace a dirty filter. A few degrees warmer upstairs is normal; a bigger gap may need duct, insulation or zoning work.
How to even out a hot upstairs
1Hot upstairs, cool downstairs
Heat rises, the roof bakes the top floor and the thermostat downstairs shuts the AC off once the first floor feels fine.
Read all the steps
- Hot upstairs, cool downstairs. Heat rises, the roof bakes the top floor and the thermostat downstairs shuts the AC off once the first floor feels fine.
- Close the blinds on the sunny side. Sun through the upstairs windows adds a lot of heat. Close blinds or curtains during the hottest hours.
- Open the vents upstairs, half-close downstairs. Open every upstairs vent all the way. Close the downstairs vents about halfway, never fully, so more air goes up.
- Set the fan to On to mix the air. With the fan on "On", the blower keeps mixing hot air from upstairs with cool air from below. If the house turns humid, go back to "Auto".
- A few degrees apart is normal. Give it a day. Two or three degrees warmer upstairs is common. A bigger gap may need duct work, insulation or a zoned system.
- Still not fixed? Call an HVAC contractor Especially if: upstairs stays much warmer than a few degrees after these changes.
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Why upstairs gets hotter
- Heat rises, and the roof and the attic heat the top floor all day.
- The thermostat is downstairs, so the AC stops when the first floor is cool.
- Upstairs ducts often run through a hot attic, and they can leak or warm up on the way.
- Too few return grilles upstairs, or closed bedroom doors, trap the hot air.
Other things that help
- Run ceiling fans upstairs counterclockwise in summer so they push air down.
- Keep bedroom doors open, or ask a technician about adding a return upstairs.
- Replace a dirty filter: the whole system moves more air.
- Some smart thermostats use a remote sensor upstairs to run the AC a little longer.
What not to do
- Do not close downstairs vents all the way. Too many closed vents can freeze the coil or strain the blower.
- Do not set the thermostat very low to force the upstairs down. The first floor gets icy and the bill goes up.
- Do not go into the attic on a hot afternoon to look at the ducts. It can get dangerously hot up there.
When to call an HVAC technician
- Upstairs stays much warmer than a few degrees after these changes.
- Barely any air comes out of the upstairs vents.
- You can see a crushed, torn or disconnected duct in the attic.
- You want to look at zoning, a ductless unit for the top floor or more attic insulation.
Frequently asked questions
Why is my upstairs so hot?
Heat rises, the attic heats the top floor and the thermostat downstairs shuts the AC off once the first floor is cool. Long or leaky attic ducts and too few returns upstairs make it worse.
Should I close downstairs vents to cool upstairs?
Partly. Close them about halfway and open the upstairs ones all the way. Do not close them fully: the system needs the airflow.
How much hotter is it normal for upstairs to be?
Two or three degrees is common in a two-story home. A gap much bigger than that usually means an airflow, duct or insulation problem worth checking.
Should I run the fan on On or Auto to cool upstairs?
"On" keeps the air moving between floors and evens out the temperature. In humid weather "Auto" removes more moisture, so switch back if the house feels sticky.
Does closing doors upstairs make it hotter?
Often, yes. A closed bedroom without its own return grille traps hot air and pushes back on the vent. Leave the doors open or leave a gap under them.
Can a technician fix uneven cooling?
Yes. They can balance the dampers, seal or add ducts, add a return upstairs or set up zoning. Sometimes a small ductless unit for the top floor is the simplest fix.