Whole House Fan Calculator

Size a whole-house fan for your home.

CFM NEEDED
CFM
for air changes

Usage Tip

Run whole-house fans when it is cooler outside than inside. Open windows first, then turn on the fan.

THE MATH
CFM = Volume × ACH ÷ 60
Where: Volume = floor area × ceiling height
• Attic vent area = CFM ÷ 750
• Whole-house fans target 30-60 ACH
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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.