ERV / Ventilation CFM Calculator
Find the fresh-air ventilation rate a home needs in CFM using the ASHRAE 62.2 formula from floor area and bedroom count.
How it works
ASHRAE 62.2: CFM = 0.03 × floor area + 7.5 × (bedrooms + 1) · ACH = CFM × 60 ÷ house volume
The ASHRAE 62.2 residential ventilation standard sets a whole-house fresh-air rate from two terms: 0.03 CFM per square foot of floor area (a proxy for the building and its furnishings) plus 7.5 CFM per occupant, estimated as the number of bedrooms plus one. An energy recovery ventilator (ERV) delivers this fresh air while transferring heat and moisture between the incoming and outgoing streams, so a tight modern home gets its required ventilation without throwing away conditioned air.
Worked example
A 2,000 ft² home with 3 bedrooms: 0.03 × 2,000 = 60 CFM, plus 7.5 × (3 + 1) = 30 CFM, totaling 90 CFM of continuous ventilation. In a 16,000 ft³ house that is 90 × 60 ÷ 16,000 ≈ 0.34 air changes per hour.
Frequently asked questions
What is the difference between an ERV and an HRV?
Both recover heat between the exhaust and fresh-air streams. An ERV also transfers moisture, which helps keep humidity in balance — useful in humid summers and dry winters — while an HRV transfers only heat and is often chosen for very cold, dry climates.
Why do bedrooms drive the ventilation rate?
ASHRAE 62.2 uses bedroom count as a stand-in for the number of occupants, assuming two people in the first bedroom and one in each additional one. More bedrooms implies more people and thus more fresh air.
Can a home be ventilated too much?
Over-ventilating wastes energy conditioning excess outdoor air and, in humid weather, can add moisture load. Matching the 62.2 rate — often run continuously at a low speed — provides healthy air without the penalty of over-ventilating.
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This calculator is for educational purposes. Double-check important results before acting on them.