Supply vents send conditioned air into a room. Return vents pull room air back toward the HVAC system. Knowing which opening you have helps you choose the right style of register, grille or vent cover.
What is a supply vent?
A supply opening is where heated or cooled air enters the room. You can often identify it when the HVAC system is running because air is blowing out of the opening. Supply registers commonly include adjustable airflow control.
What is a return vent?
A return opening draws air from the room back into the HVAC system so it can be conditioned again. Return openings are often larger and commonly use a grille without a damper. Some return-air setups also include a filter grille, but not every return opening holds a filter.
Supply vs. return at a glance
| Supply | Return | |
|---|---|---|
| Air direction | Into the room | Back to HVAC system |
| Common cover type | Register or diffuser | Grille or return-air cover |
| Airflow adjustment | Often available | Usually not needed at the cover |
| Typical size | Often smaller | Often larger, but varies |
How to identify your opening
- Run the HVAC fan.
- Hold your hand near the opening without blocking it.
- If air blows into the room, it is a supply. If air is being drawn toward the opening, it is a return.
Why the distinction matters
A cover is part of the airflow path. Do not block or substantially restrict a return opening simply to make it less visible. When replacing a cover, match the application and the duct-opening size, and preserve the airflow function the HVAC system was designed to use.
Measure after you identify the application
Once you know whether the opening is supply or return, remove the old cover and measure the duct opening edge to edge. See How to Measure Vent Covers for the full process.