FreeHVACCalculators

Start here

Menu

Whole House Fan Size Calculator

Find the airflow range a whole-house fan should deliver for your home, from its floor area and ceiling height.

Method reviewed October 26, 2026. Version 1.0.0. How it works

Your inputs

Unit system

Result

Minimum fan airflow
4,000CFM
Upper end of the range
8,000CFM

Look for a fan rated about 4,000–8,000 CFM at 0.1 in. w.c.

  • Choose a fan by its rated airflow at about 0.1 in. w.c. static pressure, as the DOE guidance says.
  • Open windows before running the fan, give the attic enough exhaust vent area for the fan’s airflow (see the fan manufacturer’s instructions), and never run it where it could pull flue gases back from a fuel-burning appliance.
Air changes per hour at the minimum
30
Show the working
  1. House volume = floor area × ceiling height
    8,000 ft³
  2. Fan airflow = ½ to 1 × volume per minute (DOE)
    4,000 – 8,000 CFM

The DOE sizing rule

DOE’s Building America fact sheet on whole house fans says to multiply the total floor area — including upstairs — by the ceiling height, and choose a fan that delivers one-half to one times that number in CFM, rated at 0.1 inch of static pressure. That is 30 to 60 air changes per hour.

For a 1,000 ft² single-story home with 8 ft ceilings, that is 4,000 to 8,000 CFM.

Installing safely

A whole-house fan needs open windows and enough attic venting to let the air out; the fan manufacturer specifies the vent area. It must never be able to pull combustion gases back down a chimney or flue, so take care in homes with fuel-burning appliances, and seal the attic opening when the fan is off.

Worked example

These are the example values the calculator opens with, and the result the engine calculates for them.

Inputs

Total floor area (all floors)
1,000 ft²
Ceiling height
8 ft

Result

Minimum fan airflow
4,000 CFM
Upper end of the range
8,000 CFM
Air changes per hour at the minimum
30

Look for a fan rated about 4,000–8,000 CFM at 0.1 in. w.c.

Assumptions

  • One-half to one house volume per minute (30–60 air changes per hour), at 0.1 in. w.c.

Limitations

  • Attic venting, fan placement and safety with fuel-burning appliances are covered by the manufacturer’s instructions and local codes.

Frequently asked questions

When does a whole house fan help?

In the evening and at night when the outdoor air is cooler than indoors, it flushes out heat quickly. It does not dehumidify, so it suits dry climates best.

Bigger or smaller within the range?

Larger fans cool faster but are noisier and need more attic vent area. Two-speed fans give flexibility.

Is a whole house fan the same as an attic fan?

No. An attic fan only ventilates the attic; a whole-house fan pulls air from the living space through open windows.

Sources

  1. Whole House Fan: Technology Fact Sheet — U.S. DOE Building America. Multiply gross floor area by ceiling height and select a fan delivering one-half to one times that number in CFM at 0.1 in. static pressure (example: 1,000 ft² × 8 ft × ½ = 4,000 cfm).

Spotted an error? Report a problem with this calculator — see our corrections policy.