Whole-House Ventilation Rate Calculator
Modern airtight homes need mechanical fresh air. Enter the floor area and number of bedrooms to find the continuous ventilation rate.
Method reviewed October 26, 2026. Version 1.0.0. How it works
Result
- Continuous ventilation rate
- 90CFM
About 90 CFM of continuous mechanical ventilation (0.34 air changes per hour).
- If your local code official requires a different rate, that rate must be used. No infiltration credit is applied here.
- Floor-area part (0.03 × area)
- 60CFM
- Occupant part (7.5 × (bedrooms + 1))
- 30CFM
- Equivalent air changes per hour
- 0.338
Show the working
- Q = 0.03 × floor area + 7.5 × (bedrooms + 1)0.03 × 2,000 + 7.5 × (3 + 1) = 60 + 30 = 90 CFM
- Air changes per hour = Q × 60 ÷ volume90 × 60 ÷ 16,000 ft³ = 0.338
The formula
The 2016 edition of ASHRAE Standard 62.2, the residential ventilation standard, sets the total whole-house rate as:
- Ventilation (CFM) = 0.03 × conditioned floor area (ft²) + 7.5 × (bedrooms + 1)
The bedroom count estimates occupants and is never taken as less than one. If your local code official requires a different rate, that rate must be used. This tool does not apply the standard’s infiltration credit, so the result is the full mechanical rate.
Putting the number to use
The result is a continuous rate. It can be supplied by an exhaust fan, a supply system or a balanced HRV or ERV running all the time. The tool also shows the equivalent air changes per hour for your ceiling height.
Kitchen and bathroom exhaust fans are sized separately: see the Exhaust Fan CFM Calculator.
Worked example
These are the example values the calculator opens with, and the result the engine calculates for them.
Inputs
- Conditioned floor area
- 2,000 ft²
- Number of bedrooms
- 3
- Average ceiling height (for air changes)
- 8 ft
Result
- Continuous ventilation rate
- 90 CFM
- Floor-area part (0.03 × area)
- 60 CFM
- Occupant part (7.5 × (bedrooms + 1))
- 30 CFM
- Equivalent air changes per hour
- 0.338
About 90 CFM of continuous mechanical ventilation (0.34 air changes per hour).
Assumptions
- Total required ventilation Qtot = 0.03 × floor area (ft²) + 7.5 × (bedrooms + 1), in CFM; bedrooms not less than one.
- Continuous operation; no credit is taken for natural infiltration.
Limitations
- This is the 2016-edition whole-dwelling formula only. Local exhaust for kitchens and baths, intermittent-fan adjustments and infiltration credits are separate provisions of the standard and are not calculated here.
- Your jurisdiction’s adopted code governs.
Frequently asked questions
Why is a studio counted as one bedroom?
The formula sets a minimum of one bedroom (two occupants), so a studio uses the same occupant allowance as a one-bedroom home.
Can a bathroom fan provide whole-house ventilation?
It can if it runs continuously at the required rate, but DOE’s Building America Solution Center does not recommend relying on a single-point exhaust fan for it.
Does every edition use the same formula?
No. This calculator uses the formula published for the 2016 edition. Check which edition, if any, your local code has adopted.
Sources
- 2016 Update for ASHRAE 62.2 (D. Prather, 2 November 2016) — ACCA HVAC Blog. Qtot = 0.03 A_floor + 7.5 × (N_br + 1), in CFM; A_floor = floor area in ft²; N_br = bedrooms, not less than one; when the authority having jurisdiction requires a different Qtot, that value must be used.
- Air Change Rates in Rooms — The Engineering ToolBox. ACH = CFM × 60 / room volume.
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