Enter the room length, width and ceiling height. You get the right blade span in inches and the minimum airflow in CFM to look for.
How it is calculated
ENERGY STAR matches the blade span, also called the diameter, to the size of the room. Multiply the room length by the width to get the area in square feet, then read the diameter from the table. The guide lists the bands as “up to 75”, “76 to 144”, “144 to 225” and “225 to 400”, so the tool puts a room of exactly 144 sq ft in the 36 to 42 inch band and exactly 225 sq ft in the 44 inch band. The guide does not cover rooms larger than 400 sq ft.
| Room area (sq ft) | Blade span |
|---|---|
| Up to 75 | 29 to 36 in. |
| 76 to 144 | 36 to 42 in. |
| 144 to 225 | 44 in. |
| 225 to 400 | 50 to 54 in. |
The airflow figure is the minimum a fan must move on its high setting to earn the label, so it is a floor to look for rather than a sizing target. It depends on the diameter D in inches. The criteria also set a minimum efficiency in cubic feet per minute per watt. A hugger fan, whose lowest blade point is within 10 inches of the ceiling, has lower minimums than a standard fan. The tool switches to the hugger figures when the ceiling is under 8 ft, which is where the guide says to use a hugger fan.
| Fan type and diameter | Minimum airflow on high (cfm) | Minimum efficiency (cfm per watt) |
|---|---|---|
| Standard, 36 in. or less | 1,767 | 0.72 × D + 41.93 |
| Standard, over 36 to under 78 in. | 250 × π × (D ÷ 24)² | 2.63 × D − 26.83 |
| Hugger, 36 in. or less | 1,414 | 0.31 × D + 36.84 |
| Hugger, over 36 to under 78 in. | 200 × π × (D ÷ 24)² | 1.75 × D − 15 |
Blade span = value from the area table
Minimum airflow on high (standard fan, 36 in. to under 78 in.) = 250 × π × (D ÷ 24)² cfm
Minimum efficiency (same fan) = 2.63 × D − 26.83 cfm per watt
Worked examples
A 14 ft by 12 ft bedroom with an 8 ft ceiling
Area = 14 × 12 = 168 sq ft, in the 144 to 225 band, so the blade span is 44 in. (112 cm).
Minimum airflow: 250 × π × (44 ÷ 24)² = 2,640 cfm. Minimum efficiency: 2.63 × 44 − 26.83 = 88.9 cfm per watt.
A 10 ft by 10 ft office, 100 sq ft
The 76 to 144 band gives 36 to 42 in. Minimum airflow runs from 1,767 cfm at 36 in. to 250 × π × (42 ÷ 24)² = 2,405 cfm at 42 in.
The same 168 sq ft room with a 7 ft ceiling
Under 8 ft the tool uses hugger fan figures. Minimum airflow at 44 in. is 200 × π × (44 ÷ 24)² = 2,112 cfm, and minimum efficiency is 1.75 × 44 − 15 = 62 cfm per watt.
Placement and ceiling height
The guide says a ceiling fan should be mounted in the middle of the room, at least 7 ft above the floor and 18 inches from the walls, and ideally 8 to 9 ft above the floor if the ceiling allows. Fans for tall ceilings use longer downrods, sold from 6 inches for a 9 ft ceiling up to 120 inches for a 20 ft ceiling, and the maker or salesperson can say which length fits your ceiling. The tool shows a reminder when the ceiling is over 9 ft.
Using the result
Match the blade span to the room first, then check the airflow and efficiency on the fan’s label or data sheet against the minimums above. A higher figure in cfm per watt means more air for the same power. If your room is larger than 400 sq ft, the guide offers no figure, so ask the fan maker which model suits it.
Frequently asked questions
What size ceiling fan for a 12 ft by 12 ft bedroom?
A 12 by 12 room is 144 sq ft, which the tool places in the 76 to 144 sq ft band: a 36 to 42 inch fan. The minimum airflow runs from 1,767 cfm at 36 inches to about 2,405 cfm at 42 inches.
How much airflow in CFM should a ceiling fan have?
A fan earns the label by moving at least 1,767 cfm on high for diameters up to 36 inches, and at least 250 × π × (D ÷ 24)² cfm for larger standard fans, where D is the diameter in inches. A 44 inch fan needs about 2,640 cfm.
What is a hugger fan, and when do I need one?
A hugger fan, also called low-profile, mounts so that its lowest blade point is within 10 inches of the ceiling. The guide points to it for ceilings under 8 ft. Its airflow minimum is lower: 200 × π × (D ÷ 24)² cfm instead of 250.
How high should a ceiling fan be mounted?
At least 7 ft above the floor, in the middle of the room and 18 inches from the walls. If the ceiling allows, 8 to 9 ft above the floor gives the best airflow.
What if my room is bigger than 400 sq ft?
The guide covers rooms up to 400 sq ft only, so the tool does not return a size above that. Ask the fan maker which model is suited to a larger room.
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Sources
Every figure on this page comes from the sources below. They were opened and checked while building the tool.