Whole-house ventilation — ASHRAE 62.2 vs the IRC give different rates for the same house

ASHRAE uses a 0.03 area coefficient, the IRC 0.01 (it assumes more natural infiltration) — 90 vs 50 CFM for the same house.

A 2,000 square foot, 3-bedroom house on the left feeds two result cards. The ASHRAE 62.2-2019 card (0.03 times area plus 7.5 times bedrooms-plus-one) works out to 90 CFM and is marked the stricter. The IRC Equation 15-1 card uses 0.01 instead of 0.03 and works out to 50 CFM, marked as assuming more infiltration. Both share the same occupant term; only the floor-area coefficient differs. — Source: ASHRAE 62.2-2019 §4.1.1 / IRC M1505.4.3

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A 2,000 square foot, 3-bedroom house on the left feeds two result cards. The ASHRAE 62.2-2019 card (0.03 times area plus 7.5 times bedrooms-plus-one) works out to 90 CFM and is marked the stricter. The IRC Equation 15-1 card uses 0.01 instead of 0.03 and works out to 50 CFM, marked as assuming more infiltration. Both share the same occupant term; only the floor-area coefficient differs.

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