Ventilation Rate Calculator
Calculate required fresh air exchange rates per Oregon Mechanical Code (OMC) and ASHRAE 62.2-2022 for residential and light commercial spaces.
Space Information
Formulas Used
ASHRAE 62.2-2022 — Residential (Section 4.1.2):
Q_fan = 0.01 × A_floor + 7.5 × (N_br + 1) [CFM]
Where A_floor = floor area (sq ft), N_br = number of bedrooms.
ASHRAE 62.2-2022 — Commercial (Ventilation Rate Procedure, Section 6):
V_bz = R_p × P_z + R_a × A_z [CFM]
Where R_p = people outdoor air rate (CFM/person), P_z = zone population, R_a = area outdoor air rate (CFM/sq ft), A_z = zone floor area.
Oregon Mechanical Code (OMC Table 403.3.1.1) — mirrors ASHRAE 62.1:
V_ot = R_p × P_z + R_a × A_z [CFM]
Air Changes per Hour (ACH):
ACH = (Q_cfm × 60) / V_room V_room = A_floor × H_ceiling [cu ft]
Altitude Density Correction:
CF = 1 / (1 - altitude_ft / 27,000) Q_corrected = Q_cfm × CF
Assumptions & References
- Residential rates per ASHRAE 62.2-2022, Section 4.1.2 whole-building ventilation formula.
- Commercial rates per ASHRAE 62.1-2019 Table 6-1 (Ventilation Rate Procedure), which Oregon OMC Table 403.3.1.1 adopts by reference.
- Oregon Mechanical Code (2021 edition) adopts ASHRAE 62.1-2019 for commercial and ASHRAE 62.2-2019 for residential ventilation minimums.
- Altitude correction applied above 1,000 ft per ASHRAE Fundamentals (density ratio method).
- Default occupant densities used when actual count is unknown (per ASHRAE 62.1 Table 6-1 default values).
- Results represent minimum outdoor air; actual system design may require more for filtration, pressurization, or energy recovery.
- Does not account for demand-controlled ventilation (DCV) reductions allowed under OMC Section 403.3.1.1 Exception 1.
- Duct leakage, filter pressure drop, and fan efficiency are outside scope of this calculator.