Ventilation Rate Calculator

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Required CFM
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Air Changes/Hour
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Exhaust Fan (CFM)
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Duct Diameter (in)
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Window Area (sq ft)

ASHRAE 62.1 Minimum Ventilation Rates (Commercial)

Occupancy CategoryRp (CFM/person)Ra (CFM/sq ft)Default Density (per 1000 sqft)
Office space50.065
Conference/meeting50.0650
Classroom (age 9+)100.1235
Restaurant dining7.50.1870
Retail sales floor7.50.1215
Gymnasium/exercise200.1840
Lobby/reception50.0610
Hotel bedroom50.0610

Source: ASHRAE Standard 62.1-2022, Table 6-1. Vbz = Rp x Pz + Ra x Az

ASHRAE 62.2 Residential Ventilation

ComponentRequirement
Whole-building ventilationQtot = 0.01 x A_floor + 7.5 x (N_br + 1)
Kitchen exhaust (intermittent)100 CFM (or 5 ACH continuous)
Bathroom exhaust (intermittent)50 CFM (or 20 CFM continuous)
Utility/laundry roomNo requirement (dryer vent separate)

Source: ASHRAE Standard 62.2-2022. N_br = number of bedrooms. A_floor in sq ft.

Natural Ventilation Guidelines

Per IRC Section R303.1, habitable rooms require openable window area of at least 4% of the floor area. Cross-ventilation (openings on two walls) is strongly recommended. Window placement high and low maximizes the stack effect for passive air movement.