Calculate the airflow (CFM) a room needs from its size, ceiling height and air changes per hour — fans, HVAC and ventilation sizing.
| Input | Result |
|---|---|
| 100 sq ft × 8 ft, 8 ACH (bathroom) | 107 CFM |
| 150 sq ft × 8 ft, 15 ACH (kitchen) | 300 CFM |
| 200 sq ft × 9 ft, 5 ACH (bedroom) | 150 CFM |
CFM = cubic feet per minute. CFM = (room area × ceiling height × air changes per hour) ÷ 60. A 100 sq ft bathroom with 8 ft ceilings at 8 ACH needs (100×8×8)÷60 ≈ 107 CFM.
Aim for 8 air changes per hour: that works out to roughly 1 CFM per square foot for standard 8 ft ceilings — the common '1 CFM per sq ft' rule. A 50 sq ft bathroom → 50 CFM minimum; add more for long duct runs.
Kitchens want ~15 ACH for cooking moisture and odors: a 150 sq ft × 8 ft kitchen needs about 300 CFM. Range hoods are sized separately at 100 CFM per 10,000 BTU of cooktop output, capped by make-up air rules.