Section 6.2.6/Exhaust Ventilation
ASHRAE 62.1 Table 6.2.6.2 specifies minimum exhaust airflow rates for spaces requiring direct exhaust, including toilet rooms, kitchens, storage rooms, and parking garages.
Spaces where contaminants are generated at rates exceeding what the supply-air system can dilute must be directly exhausted per Table 6.2.6.2. Toilet rooms and bathrooms require exhaust at 70 CFM per water closet or urinal or 50 CFM per room for private bathrooms. Kitchens (commercial) require exhaust through cooking hoods per ASHRAE 154 or the IMC. Janitor closets and storage rooms require 1.0 CFM per square foot. Parking garages require 0.75 CFM per square foot or a CO-based demand control system. Locker rooms require 0.5 CFM per square foot. The exhaust air must be discharged directly outdoors and not recirculated. Where transfer air from adjacent spaces provides the makeup air for the exhausted space, the transfer opening must be sized adequately and the adjacent space outdoor air must include the transfer component. Exhaust rates from Table 6.2.6.2 are independent of the supply-air outdoor ventilation rates from Table 6.2.2.1.
Why this section exists
Some spaces generate contaminants (odors, moisture, chemical fumes, vehicle exhaust) at concentrations that cannot be adequately diluted by the general ventilation system. Direct exhaust removes these contaminants at the source before they spread to adjacent spaces. Toilet room exhaust prevents odors from migrating into corridors and offices. Kitchen exhaust removes grease-laden air, combustion products, and cooking odors. Parking garage exhaust removes carbon monoxide and nitrogen dioxide from vehicle engines. The exhaust rates in the table are minimum values based on contaminant generation rates and acceptable concentration limits.
What plan reviewers look for
Plan reviewers check the mechanical drawings for exhaust fans serving toilet rooms, kitchens, janitor closets, and parking garages. They verify the exhaust CFM matches Table 6.2.6.2 for the space type and size. They check that exhaust discharges outdoors and not into a return air plenum. They verify makeup air provisions: either dedicated makeup air or transfer air from adjacent spaces with adequately sized transfer openings. For parking garages, they check whether a CO-based demand control system is used as an alternative to constant exhaust. They verify coordination with the IMC exhaust requirements.