Said It Here

What to do when your return air vent is too small

An undersized return air intake causes the AC condenser to choke, creating loud noises outside and terrible system efficiency. Routing additional returns through walls and crawlspaces is difficult work that typically requires a professional.

What people tried

Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.

  1. 1
    Adding at least two more intake vents up in the attic to provide enough airflow
  2. 2
    Cutting out and enlarging the current intake vent to make the new grille about double the size
  3. 3
    Cutting a hole directly into the plenum or furnace pedestal
  4. 4
    Routing additional returns through the crawlspace or walls
  5. 5
    Framing out channels using thermopan and tape
  6. 6
    Opening up the floor joists under the return to act as a panned section

In their words

Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.

r/hvacadvice2 people · September 2026 – October 2026

“My 3 too AC unit has two 8 inch return ducts which are wayyy undersized for the unit. I’m getting terrible efficiency and want to improve.”source ↗

“Routing additional returns through the crawlspace and in the wall seems really difficult and would require a professional.”source ↗

PhiKap15 · r/hvacadvice · 8 upvotes

“We’ve been experiencing issues with the condenser outside making a new loud noise so I called out a new HVAC company to take a look at what my last contractor installed.”source ↗

“the contractor told me our current return air intake is too small for this system.”source ↗

“Clearly there is something wrong because the condenser seems to be “choking” but everything I’ve read online makes it seem like even though our current return vent is slight too small for a 5-ton, double the size isn’t necessary.”source ↗

Scouting4Bacon · r/hvacadvice

Where this came up

r/hvacadviceairflowdiyheating and coolinghome improvementhome maintenancehvac

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