ASHRAE 62.2 Whole-House Mechanical Ventilation Rate

ScopeQtot = 0.03 x conditioned floor area + 7.5 x (bedrooms + 1) (ASHRAE 62.2-2019), and the continuous fan the installer must provide, Qtot minus Phi x the infiltration credit x Aext (Eq. 4.2): the full credit for a balanced system, a Qinf / Qtot share of it for an exhaust- or supply-only one, and Aext the exterior share of the envelope for an attached unit (1 for a detached house). The tighter the house tests, the smaller the credit and the larger the fan 62.2 requires - the trade-off a blower-door retest makes concrete. The conservative default is zero credit. Local kitchen/bath exhaust is separate. A sizing aid, not a 62.2 compliance certificate.

Formula or tableq_tot = 0.03 x floor_area_ft2 + 7.5 x (bedrooms + 1); q_fan = max(0, q_tot - Phi x infil_credit_cfm x Aext), Phi = 1 balanced or infil_credit / q_tot unbalanced (ASHRAE 62.2 Eq. 4.2); verdict = q_fan > 0 (fan required) else (credit meets Qtot).

Source and editionASHRAE 62.2-2019 §4.1 whole-house ventilation rate (Qtot = 0.03 x Afloor + 7.5 x (Nbr + 1)) and the fan flow Qfan = Qtot - Phi (Qinf x Aext) (Eq. 4.2), by name; the 0.03 cfm/ft^2 and 7.5 cfm/person are the standard's rate coefficients.

Free accessThe whole-house ventilation rate and the fan-flow relation are stated in ASHRAE 62.2-2019 §4.1; the arithmetic is public. The infiltration credit comes from the measured air-tightness.

What governsEstimate. AHJ and licensed professional govern.

API field namesfloor_area_ft2, bedrooms, q_tot, q_fan

• Total required Qtot Qtot = 0.03 x conditioned floor area + 7.5 x (bedrooms + 1); occupants assumed Nbr + 1ASHRAE 62.2-2019 §4.1
• Fan flow Qfan = max(0, Qtot - Phi x infiltration credit x Aext), Phi = 1 balanced or Qinf / Qtot unbalanced; the tighter the house, the smaller the credit and the larger the fanASHRAE 62.2-2019
• Infiltration credit the credit is the blower-door natural infiltration; the conservative default is zerofirst principles