How to tell which house vents are returns?
Supply vents blow conditioned air into a room while return vents pull air back into the HVAC system. Because new systems or unlabelled grilles lack obvious airflow, homeowners struggle to tell them apart using simple tests like holding up paper towels, which stops them from properly balancing airflow or changing filters.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
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How to tell which house vents are returns?
- 1testing vents with a paper towel to check for suctionDid this help you?
- 2checking if registers have adjustable louvers or dampersDid this help you?
- 3going up into the attic to follow the ductworkDid this help you?
- 4Turning appliances or utilities on one at a time to see if they exhaust air through the ventDid this help you?
- 5Installing a grate over the unknown vent openingDid this help you?
- 6Turning on individual bathroom exhaust fans or appliances one at a time while checking outside for airflow.Did this help you?
- 7Holding a sheet of paper to the vent to see if it gets sucked up or fallsDid this help you?
- 8Investigating ductwork in the attic for dampers stuck closed or damaged ductingDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“Are those vents return vents? The other clearly identified return vents in the house also get dusty so I am assuming these in the room are return as well collecting all the dust in the air but since they have the same covers as the supply idk. Are these returns or broken supply’s?”source ↗
“And if anyone knows how to stop mold getting on the other vents that would be wonderful!”source ↗
“i tried testing which vents are return vents by using paper towel to see if it sucks it up (google said so) none of them seem to though itsa new hvac too at least the hvac itself im not sure if vents were touched up when previous owners got a new one”source ↗
“I’m trying to decide where the dryer vent and air intake for the air exchanger are.”source ↗
“I was wondering if it was the exhaust for the bathrooms. Definitely could be. Thanks I’ll turn some stuff on and see what happens!”source ↗