return air

The mechanism in an HVAC system that pulls stale, unconditioned air out of a spaces and cycles it back to the furnace or air conditioner to be reheated or cooled; it works in a continuous loop with the supply vents to regulate indoor air pressure, filter out dust, and maintain even temperatures.

Definition source: English Wiktionary via Wiktextract

Usage: uncountable

No example sentence was provided for this meaning.