There are two ways for calculating the volume of the exhaust air for restrooms:
- Using number of air changes: the practical number of air change for restrooms is 6-10 air changes, which creates a good ventilation but it is not always an energy efficient system.
- Using ASHRAE standards: ASHRAE 62.1 recommends a 50 cfm exhaust air for each odor generated fixture such as toilet and urinal.
The makeup air for restroom exhaust can either be provided from outside air or adjacent area indoor air, which can take a partial of the space return air to restroom as makeup air.
