Vent, Valve & Volt
Weak airflow from vents, or one room hotter or colder than the rest

You can fix this

Likely cause: a clogged air filter

A clogged filter chokes airflow to every vent in the house. Replace it and the airflow should come back.

Why this happens

A Coalinga College HVAC course on LibreTexts lists dirty filters first among the causes of weak airflow, and Hoffmann Brothers, an HVAC contractor, puts filters at the top of its list too. Every bit of air the system moves has to pass through the filter, so a clogged one weakens every vent at once. Trane recommends replacing the filter every 1 to 3 months.

How to fix it

  1. Set the thermostat to Off before you pull the filter.
  2. Replace the filter with the same size, arrow pointing toward the furnace or air handler.
  3. Set the thermostat back to your normal setting and check the vents after several minutes.
  4. Write the date on the new filter's edge so you know when it's due again.

When to stop. If airflow is still weak everywhere with a clean filter, call an HVAC technician to check the blower.

If this does not fix it, tell the HVAC technician

  • How dirty the filter was and when it was last changed.
  • Whether airflow improved after a new filter.
  • Whether you've seen ice on the lines or coil.

Build the full list: what to tell the HVAC technician.

Start this troubleshooter over

References (every fact above comes from one of these pages)
  1. LibreTexts (Coalinga College HVAC course): Common air distribution problems and solutions
  2. Hoffmann Brothers: What triggers low airflow from AC vents
  3. Trane: AC not blowing cold air

Vent, Valve & Volt is published by the team behind FourHome. Browse all FourHome replacement faucet and shower parts on the FourHome Amazon store.