calcs.homes
calcs.homes
Enter your room's dimensions and type to size an exhaust fan — bathroom, kitchen, and laundry rooms each need a different air-change rate.
Estimate only — ducting length and bends reduce a fan's real-world airflow below its rating.
CFM = room volume × target air changes per hour ÷ 60. Bathrooms and laundry rooms typically target 8 air changes per hour, kitchens closer to 15 due to cooking moisture and odors. We round up to the nearest common retail fan size (50, 80, 110, 150, 190, or 250 CFM) since that's what's actually sold.
A common rule of thumb is 1 CFM per square foot for bathrooms up to 100 sq ft — this calculator uses the more precise volume-based HVI formula, which accounts for ceiling height too.
Yes — long duct runs and elbow bends add resistance that reduces actual airflow below the fan's rated CFM. For long runs, size up or choose an in-line duct booster fan.