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Ventilation Rules of Thumb

Office Building

Office Building

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According to ASHRAE Standard 62.1, an office will require 4-10 air changes per hour depending on the occupancy and size of the office. The illustration above demonstrates how to ventilate more than one area using a single fan. To determine the amount of CFM required for your ventilation equipment, calculate the volume of the room (LxWxH) and divide it by the number of minutes per air change. For example:

Office A: 18'L x 18'W x 15'H = 4,860 ft3
4 Air changes per hour : 60 mins. / 4 = 15 minutes
4,860 ft3 / 15 minutes per air change
324 CFM
Office B: 24'L x 24'W x 12'H = 6,912 ft3
6 Air changes per hour : 60 mins. / 6 = 10 minutes
6,912 ft3 / 10 minutes per air change
691 CFM

TOTAL CFM required for the exhaust fan = 1,015 CFM