Symptoms
- Air trickles out of vents instead of blowing steadily
- Some or all rooms affected
- Furnace may run longer to compensate
Likely causes
- CommonClogged air filterThis is the single most common cause of weak airflow throughout a house.
- CommonClosed or partially closed dampers or ventsDampers in ductwork or registers can be nudged closed without anyone noticing.
- PossibleBlower motor weakening with ageAn aging or failing motor can't push air as forcefully as it used to.
- PossibleDuct leaks or disconnectionsAir escaping into an attic or crawlspace never reaches the vent.
- Less commonUndersized or crushed ductworkDucts crushed during storage use or a poor install restrict flow permanently.
What to do
- Replace the air filter and confirm airflow improves.
- Check all registers and any visible dampers in the ductwork are open.
- Feel airflow at multiple vents to see if it's a whole-house issue or isolated to certain rooms.
- Listen to the blower; a noticeably weaker or straining sound can indicate motor wear.
- Check accessible ductwork in the attic, basement, or crawlspace for obvious leaks, disconnections, or crushed sections.
- If airflow stays weak after filter and vent checks, have a technician test the blower motor and inspect ductwork.
Tools and parts
- Flashlight
Furnace air filterSearch: “furnace air filter size replacement”
When to call a pro
Call an HVAC technician if airflow stays weak after checking the filter and vents; the blower motor or ductwork may need repair.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.