Ceiling Fan Sizes: What Size Fan, CFM and Motors
Match blade span to floor area, about 44 inches for a small bedroom up to 84 inches for a great room, then compare airflow (CFM) and efficiency (CFM per watt).
By Karson AbernathyContributing writer.
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The short answer
Ceiling fans are sized by blade span: the diameter of the circle the blade tips sweep. Pick the span from the floor area of the room. Big Ass Fans publishes this guide for its residential models:
| Room size | Example room | Fan diameter |
|---|---|---|
| Up to 144 sq ft | Small bedroom, office | 44 in |
| Up to 225 sq ft | Standard bedroom, den | 52 in |
| Up to 400 sq ft | Living room, main suite | 60 in |
| Up to 900 sq ft | Great room, open plan | 84 in |
If a room falls between two sizes, the same guide says to go up a size: a bigger fan on a lower speed moves the air more gently and quietly than a small fan on high.
To get the square footage, multiply the room's length by its width in feet. A 12 by 12 foot bedroom is 144 square feet.
Ceiling height and mounting
Height changes which fan works:
- 8-foot ceilings: a flush-mount (hugger) fan sits close to the ceiling. ENERGY STAR defines a hugger fan as one whose blades sit 10 inches or less below the ceiling.
- 9 to 10-foot ceilings: a standard downrod, which Big Ass Fans says is typically 12 inches on its models.
- Higher ceilings: a longer downrod. Big Ass Fans advises keeping the blades at least 7 feet above the floor, ideally 8 to 9 feet.
Mount the fan on an electrical box listed for ceiling fan use; ENERGY STAR notes fans can weigh as much as 50 pounds.
What CFM means on a ceiling fan
CFM is cubic feet per minute: how much air the fan moves. Two numbers matter on the box:
- Airflow (CFM): the total air moved at high speed. Higher means a stronger breeze.
- Efficiency (CFM per watt): airflow for each watt of power. Higher means cheaper to run for the same breeze.
ENERGY STAR sets minimums for both that rise with fan size. For a standard (not hugger) fan between 36 and 78 inches, the program's formulas work out to:
| Fan size | Minimum airflow, high speed | Minimum efficiency |
|---|---|---|
| 44 in | 2,640 CFM | 88.9 CFM/W |
| 52 in | 3,687 CFM | 109.9 CFM/W |
| 60 in | 4,909 CFM | 131.0 CFM/W |
| 72 in | 7,069 CFM | 162.5 CFM/W |
Use these as a floor when you compare two fans of the same size. ENERGY STAR says certified fans are up to 44% more efficient than conventional fans.
DC vs AC ceiling fan motor
An AC motor runs straight off household current. A DC fan has electronics that convert the supply to drive a brushless DC motor, which is built for low power draw. Big Ass Fans says the brushless DC motors in its home fans draw as little as 2.4 watts at low speed. ENERGY STAR credits improved motors and blade designs for the gap between certified and conventional fans. When you compare an AC and a DC fan of the same size, the CFM per watt figure on each box shows the difference in running cost directly.
Using the fan year round
ENERGY STAR advises running the fan counterclockwise in summer for a cooling breeze and clockwise on low in winter to push warm air down from the ceiling. A fan cools people, not the room, so switch it off when you leave. Ceiling fans sit in the tools and home improvement department.