Ceiling Fans and A/C: What They Do, and the Mistake Most People Make
Fans cool people, not rooms. Used correctly they let you raise the thermostat several degrees; left running in empty rooms they just cost money.
Ceiling fans do not lower room temperature — they create a wind-chill effect on skin that makes a room feel three to four degrees cooler. Used in occupied rooms, that lets you raise the thermostat several degrees and save real money. Running fans in empty rooms wastes electricity and adds a small amount of heat from the motor.
The thing to understand first
A ceiling fan does not cool air. It moves it. The cooling sensation comes from increased evaporation off your skin and from breaking up the thin layer of warm air that sits against you in still conditions.
That effect is worth roughly three to four degrees of perceived temperature for most people. It is entirely real — and it only exists where there is a person.
The corollary is the mistake: a fan running in an empty room is converting electricity into a tiny amount of heat and nothing else. Every fan in the house running around the clock is not a cooling strategy.
How to actually save money with them
Turn the fan on in the room you are in, then raise the thermostat three or four degrees. The room feels the same to you and the air conditioner runs meaningfully less.
In Phoenix, where the cooling season runs eight months, that adds up. Going from 76 to 79 with a fan on is a significant reduction in runtime over a summer — and the fan itself uses a small fraction of what the air conditioner uses.
Turn it off when you leave the room. That single habit is the difference between fans saving money and costing it.
Direction: which way in summer
In summer, blades should turn counterclockwise when viewed from below, pushing air straight down. That downdraft is what produces the wind-chill effect.
In winter, reverse to clockwise at low speed. That pulls air up the center and pushes it gently down the walls, circulating warm air that has collected at the ceiling without creating a draft. In a Valley home with high or vaulted ceilings this is worth doing.
Most fans have a small switch on the motor housing. Almost nobody uses it, and in a two-story home with vaulted ceilings the winter setting is genuinely useful.
What about the whole-house fan?
A whole-house fan mounted in the ceiling pulls air from the house and exhausts it into the attic, drawing outside air through open windows. It works beautifully in climates with cool nights.
In Phoenix its usefulness is seasonal. In April, May, October, and November, when evening temperatures drop into the 70s, a whole-house fan can flush the day's heat out of a house quickly and let you avoid running the air conditioner entirely on shoulder-season evenings.
In July, when overnight lows stay in the 90s, it does nothing useful. And during monsoon it pulls humid air into the house. So: a legitimately valuable tool for perhaps four months of the year here, which is worth knowing before spending on one.
Fan sizing and placement
| Room size | Fan diameter |
|---|---|
| Up to 75 sq ft | 29–36 inches |
| 75–144 sq ft | 36–42 inches |
| 144–225 sq ft | 44–50 inches |
| 225–400 sq ft | 50–60 inches |
| Over 400 sq ft | Two fans, or a 60"+ fan |
Blades should sit eight to nine feet above the floor and at least eighteen inches from the nearest wall. On a vaulted ceiling, a downrod that brings the fan to that height matters — a fan mounted tight to a twelve-foot peak moves very little air where people actually are.
The outdoor version
Patio fans extend the usable season on a covered Arizona patio considerably. Moving air plus shade makes a 95-degree evening pleasant rather than oppressive, and misting systems combined with fans work extremely well during our dry months.
Make sure any fan installed outdoors is rated for damp or wet locations. An indoor-rated fan on a Phoenix patio will fail, usually during monsoon.
Frequently asked
Do ceiling fans actually lower the temperature?
No. They create a wind-chill effect on skin that makes a room feel three to four degrees cooler, but the air temperature is unchanged. That is why a fan in an empty room accomplishes nothing except using electricity.
Which way should a ceiling fan turn in summer?
Counterclockwise when viewed from below, pushing air straight down. In winter, reverse to clockwise at low speed to circulate warm air off the ceiling without creating a draft. Most fans have a small switch on the motor housing.
How much can ceiling fans save on cooling costs?
Used correctly — on in occupied rooms, thermostat raised three to four degrees — the savings over an eight-month Phoenix cooling season are meaningful. The fan uses a small fraction of what the air conditioner does. Left running in empty rooms, they cost money instead.