A whole house fan is simple to run once you know the rhythm: open up when it cools off outside, close up before it warms. Here is the routine, plus the mistakes to avoid.
Use a whole house fan when it is cooler outside than inside. CentricAir suggests waiting until it is at least 10 degrees cooler, usually after sunset. Close any fireplace damper, open windows in the rooms you want cooled, keep interior doors open, and turn the fan on. Building America recommends about 4 square feet of open window per 1,000 CFM. Before it warms up outside the next morning, turn the fan off and close the windows to hold the cool air in.
The goal is to swap the warm air trapped in your house for cooler outdoor air, and then hold onto that cool air as long as you can. Everything below serves one of those two jobs.
How do you use a whole house fan?
Seven steps, built from CentricAir’s operating instructions.
- Wait for the crossover.Turn the fan on once it is cooler outside than inside. CentricAir suggests at least 10 degrees cooler, usually in the evening, at night or early morning.
- Close the fireplace damper.CentricAir advises closing it first so the fan does not pull soot into the room.
- Open windows.Open windows in the rooms you want to cool. You can close windows in other rooms to focus the airflow where you need it.
- Open interior doors.Leave doors open between those rooms and the fan so air can move freely.
- Turn the fan on.Start on high to flush the day’s heat, then drop to low if you want quieter running.
- Set a timer.A timer or temperature control shuts the fan off for you.
- Close up in the morning.Before it warms up outside, turn the fan off and close the windows. The house stays cool longer.
How many windows should you open?
About 4 square feet of open window for every 1,000 CFM of fan airflow.
That is the Department of Energy’s Building America guideline. For a CentricAir 3.4, rated at 3,242 CFM, that works out to roughly 13 square feet of open window. Too little window area makes the fan work harder and can pull air from places you do not want, like the fireplace. CentricAir also warns against concentrating all of the suction in one spot. Our guide to which windows to open goes room by room.
When is the best time to run it?
Evening, overnight and early morning, whenever it is cooler outside.
Building America says whole house fans work best where summer nights drop below about 67°F. In many dry western climates, that means you can run the fan from sunset to morning. Turn it off during the day once the outside temperature climbs above the inside temperature. See our best time to run a whole house fan and heat wave guides for more.
Should you use high or low speed?
High to cool the house fast, low for quieter overnight running.
On a CentricAir 3.4, high speed moves 3,242 CFM and low moves 1,409 CFM, with listed noise of 49 and 47 dBA. Many owners flush the house on high for the first part of the evening, then switch to low for the night. Our noise guide lists every model.
What mistakes should you avoid?
- Running it with the windows shut. The fan has nothing to pull from. Open windows and close the fireplace damper before the fan starts.
- Running it with the AC on. The fan would push your cooled air into the attic.
- Running it when it is warmer outside. You will pull hot air in.
- Running it on humid nights. A whole house fan cannot remove moisture the way an air conditioner can.
- Forgetting to close up. Leaving windows open into the morning lets the heat back in.
What control makes this easiest?
One with a timer and a temperature setting.
A timer shuts the fan off after the hours you choose. A temperature setting stops it once the house is cool. CentricAir’s 2 speed remote and wired wall switch offer both, with timers from 1 to 12 hours.
See every CentricAir control, from simple timers to temperature control.
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Frequently asked questions
When should I turn on my whole house fan?
When it is cooler outside than inside. CentricAir suggests waiting until it is at least 10 degrees cooler outdoors, usually in the evening, overnight or early morning.
How many windows should be open?
Enough for the fan’s airflow. Building America recommends about 4 square feet of open window for every 1,000 CFM. Open the windows in the rooms you want cooled first.
Should I leave the whole house fan on all night?
You can, if it stays cooler outside than in. Use a timer or temperature control so it shuts off before the morning warms up or the house gets too cold.
Should interior doors be open or closed?
Open, between the rooms you want cooled and the fan. CentricAir’s guidance is to keep interior doors open so the cool air can move through the house.
What should I do before turning on a whole house fan?
Open windows and close any fireplace damper. CentricAir advises both so the fan does not pull hard on one spot or draw soot into the room.
Keep reading
Sources
- CentricAir, Instructions for Operating a Whole House Fan (Jan. 13, 2015) and How to Cool Your Home with a Whole House Fan, accessed Sept. 2026.
- U.S. Department of Energy, Building America Solution Center (PNNL), Whole-House Fans, updated Sept. 29, 2022.
- CentricAir 1.5, 2.0, 2.7, 3.4, 4.0 and 4.0 ECM product pages (specifications tab), centricair.com, accessed Sept. 30, 2026.