An air diffuser is a duct terminal device that disperses conditioned air into occupied spaces while mixing it with room air to prevent drafts and temperature stratification. Diffusers reduce air velocity from 500-1200 feet per minute in ducts to 50-100 feet per minute at face level, creating comfortable air distribution patterns.
Types and Design
Common diffuser styles include ceiling diffusers with rectangular or round configurations, sidewall diffusers, and linear slot diffusers. Each design features adjustable dampers or deflector vanes that direct airflow at specific angles. Face areas typically range from 100 to 400 square inches with Noise Criterion ratings from 25 to 40. Diffusers achieve effective throw distances of 8 to 20 feet depending on velocity and blade angles.
Sizing and Performance
Proper diffuser selection requires calculating required CFM and matching to unit throw and velocity characteristics. Undersized diffusers cause excessive noise and velocity, while oversized units create stagnant zones. Installation height and proximity to walls significantly affect performance. Diffusers should have effective area ratings and pressure drop specifications for accurate duct design calculations.