An air outlet is the device at the end of a ventilation duct, such as a diffuser, grille or register, that delivers air into a space and shapes how it spreads.
- Also called
- Diffuser, grille, register
- Where you see it
- Ventilation systems, including enclosed parking garages
- Key fact
- IMC 404: 0.75 cfm per sq ft garage exhaust, down to 0.05 with demand-controlled ventilation
Outlets are selected for airflow, throw (how far the air travels), noise and pattern. Their counterparts, return and exhaust inlets, pull air out. Together their placement decides whether fresh air reaches the whole space or short-circuits from supply to exhaust.
In enclosed parking garages
- Garage ventilation must dilute and remove carbon monoxide and nitrogen dioxide from vehicle exhaust, so supply and exhaust locations are arranged to sweep the full floor.
- Many garages use jet fans instead of ducted outlets, pushing air across the floor toward exhaust points.
- International Mechanical Code Section 404 sets a minimum exhaust rate of 0.75 cfm per square foot for enclosed parking garages, and allows reduction to 0.05 cfm per square foot when demand-controlled ventilation with gas detection is used.
The Parkonomics view
Ventilation is one of the largest operating costs in an enclosed garage, and outlet layout decides how much of that air does useful work. Pair good air distribution with demand-controlled ventilation and the fans can run at a fraction of full speed most of the day.
Related terms: Demand-Controlled Ventilation, Variable Frequency Drive, Enclosed Parking Garage
Further reading: The Evolution of U.S. Parking Structures in 2026