Ventilation Rate Calculator (ASHRAE 62.2)
Calculate the required whole-building mechanical ventilation rate for residential buildings per ASHRAE Standard 62.2-2022.
Formula
ASHRAE 62.2-2022, Equation 4.1a — Whole-Building Ventilation Rate:
Qfan = 0.03 × Afloor + 7.5 × (Nbr + 1)
- Qfan — Required mechanical ventilation rate (CFM)
- Afloor — Conditioned floor area (ft²)
- Nbr — Number of bedrooms (occupants default = Nbr + 1)
Infiltration Credit (Section 4.1.3):
Qnet = max(Qfan − 0.5 × Qinf, 0)
Fan Power: P (W) = Qnet × η (W/CFM)
Annual Energy: E (kWh/yr) = P × 8,760 / 1,000
Assumptions & References
- Based on ASHRAE Standard 62.2-2022: Ventilation and Acceptable Indoor Air Quality in Residential Buildings.
- Default occupant load = number of bedrooms + 1 (per ASHRAE 62.2 Table 4.1a).
- The 0.03 CFM/ft² term accounts for building material off-gassing; the 7.5 CFM/person term accounts for occupant bioeffluents.
- Infiltration credit of up to 50% of measured infiltration (Qinf) may be applied when a blower door test is performed per Section 4.1.3.
- ACH estimate assumes a uniform ceiling height of 8 ft; adjust for actual building volume.
- Fan power assumes continuous operation; intermittent ventilation requires adjusted flow rates per ASHRAE 62.2 Table 4.2.
- This calculator covers whole-building ventilation only; local exhaust (kitchen, bath) requirements are addressed separately in Section 5.
- Does not account for heat/energy recovery ventilators (HRV/ERV) efficiency adjustments.
- Applicable to single-family and low-rise multifamily residential buildings ≤ 3 stories.