Why does the calculation use bedrooms instead of actual occupants?

Q: How much whole-house ventilation does ASHRAE 62.2 require for a 2000 sq ft, 3-bedroom house?

Using the ASHRAE 62.2-2019 formula Qtot = 0.03 x Afloor + 7.5 x (Nbr + 1), a 2000 sq ft, 3-bedroom home needs 0.03 x 2000 = 60 CFM from floor area plus 7.5 x 4 = 30 CFM from occupants, for 90 CFM of continuous airflow. That is the continuous whole-house rate before any local exhaust is added.

Q: Does this number include bathroom and kitchen exhaust fans?

No. This is only the continuous whole-house ventilation rate. ASHRAE 62.2 requires local exhaust separately: 50 CFM intermittent (or 20 CFM continuous) in each bathroom and 100 CFM intermittent in kitchens, which you size in addition to this figure.

Question

Why does the calculation use bedrooms instead of actual occupants?

Accepted Answer

ASHRAE 62.2 uses bedroom count as a standardized proxy for occupancy, assuming the number of occupants equals bedrooms plus one. This avoids guessing future occupancy and is why the occupant term is 7.5 x (Nbr + 1). Leakier homes may also get an infiltration credit under the 62.2-2019 infiltration adjustment, which this tool does not apply.

Why does the calculation use bedrooms instead of actual occupants?

Answers