Most commercial buildings are run slightly positive, a few hundredths of an inch of water column, so humid, dusty or polluted outdoor air is kept out and air leaks outward instead. Restaurants, labs and toilet rooms exhaust a lot of air and need matching makeup air or the building goes negative. Signs of a negative building include doors that slam or stick, cold drafts, sewer odors and flue gas spilling from water heaters.
Building pressurization is negative 0.04 with the hoods on, front door whistles and the water heater is spilling.
Also heard as
- pressurization
Related terms
Stack effect
The buoyancy-driven airflow that pushes warm air out the top of a building and pulls outdoor air in at the bottom.
Return air
Air drawn back from the conditioned space to the air handler to be filtered and conditioned again.
ACH
Air changes per hour: how many times a space's full air volume is replaced in one hour.
Ventilation rate
The amount of outdoor air deliberately brought into a space to dilute indoor contaminants, usually in cfm per person and per square foot.