What is the difference between a hot and a cold air register?

Hot air registers (aka supply vents) blow warm air out from your furnace to heat your home. Cold air registers (aka returns) pull the air back in to be reheated or cooled. You’ll usually find hot air vents on the floor, while cold air returns are often on walls or ceilings. Together, they keep your home comfy by circulating air efficiently — like a tag team of toasty and breezy.