Little or no air is coming from your vents
One room or the whole house? The answer sends you in two completely different directions.
Is this an emergency?
Not an emergency, but don’t leave it a season.
You’re probably seeing
- Air barely moves at the registers even with the fan running
- One or two rooms are noticeably weaker than the rest
- The system runs constantly but rooms never reach temperature
- Whistling at the return grille, or vents that hum loudly
- Ice visible on the indoor coil or the copper line
What it probably is
A clogged air filter
Most common whole-house causeWeak at every register, and the filter is grey against the light. The cheapest and most common cause by a distance.
Closed, blocked or painted-over registers
Most common single-room causeWeak in specific rooms. Furniture over a floor vent and a damper lever left shut after last season are both routine.
A disconnected or crushed flex duct
Common, and often visible once someone looksOne room with almost no air while the rest are fine. Common in attics and crawl spaces where a run has been stood on or knocked off its collar.
A frozen evaporator coil
Common in cooling seasonAirflow fades over hours rather than suddenly, and there is ice on the coil or the line. Usually caused by the filter or low refrigerant.
A failing blower motor or a slipping belt
Less common - a technician jobWeak everywhere, often with a new noise - a squeal, a rumble, or a motor that runs hot and cuts out after a while.
Undersized or leaking ductwork
Common in older homes - a design problem, not a faultThe house has always been like this, or got worse after a renovation. Leaky duct in an unconditioned attic loses conditioned air before it reaches the room.
What to do before anyone arrives
Walk the house with the fan set to ON and check every register
This single test decides everything that follows. Hold a hand or a sheet of tissue at each vent. Note which rooms are weak. Whole-house weakness and single-room weakness are different problems with different fixes.
Replace the air filter
If it is grey against a light, change it. On whole-house weakness this resolves a large share of complaints on its own, and it costs a few dollars.
Do not fit a much denser filter than the system was designed for. A very high MERV filter on a system not specified for it restricts airflow and can cause the exact symptom you are trying to fix.
Open every register and clear anything covering them
Check the small lever on each register is open, and move rugs and furniture off floor vents. Closing vents in unused rooms is popular advice and it raises duct pressure rather than saving money.
Check the return grille, not just the supply vents
A system can only push out what it can pull in. Returns are often large grilles in a hallway or ceiling, and they get blocked by furniture or left filthy for years.
Look for ice on the indoor coil or the copper line
If you find ice, switch cooling OFF and set the fan to ON to thaw it - several hours, typically. Airflow will not return until it has melted.
Do not chip or melt ice. Running a system with a frozen coil risks the compressor.
If it is one room, say so when you book
Tell the technician which rooms are weak and which are fine. That points them at duct inspection rather than equipment diagnosis, and it is the difference between an accurate visit and a wasted one.
This is the end of the homeowner sequence. Do not climb into an attic in summer heat to look for ducts yourself, and do not open the blower compartment.
What it costs to fix
Ranges below are for the repair itself. For full replacement pricing see the hvac cost guides.
| What it is | What the part costs | What decides your bill |
|---|---|---|
| New air filter | A few dollars | Nothing - this one is yours |
| Opening dampers and clearing vents | Free | Nothing |
| Reconnecting a dropped flex duct | Little or no part | Access - an attic run in August is a different job from a basement one |
| Sealing leaky duct joints | Materials are inexpensive | How much of the run is reachable |
| Blower motor or capacitor | A modest part | Mostly labour, plus diagnosis |
| Duct redesign for an undersized run | A project, not a repair | This is remodelling, and worth a second opinion |
U.S. Bureau of Labor Statistics, Occupational Outlook Handbook (May 2025 wage data).
The important pattern: most single-room airflow complaints are duct problems with small parts costs and moderate labour, not equipment failures. If the first recommendation you receive is a new system and nobody has been into the attic or crawl space, get another quote. Labour anchor: the national median wage for HVAC mechanics and installers is $29.33 an hour (BLS, May 2025), billed on top of a diagnostic call.
Can I fix this myself?
Attics and crawl spaces are the two places homeowners get hurt chasing this problem. Attic temperatures in summer can be dangerous, ceiling joists are not a floor, and insulation hides both. If the diagnosis points to ductwork above or below the living space, that is a visit, not an afternoon.
Reasonable to DIY
- Testing every register with the fan on
- Replacing the air filter
- Opening dampers and clearing blocked vents and returns
- Thawing a frozen coil with the fan only
- Noting exactly which rooms are affected
Call a pro
- Any work inside the blower compartment
- Reconnecting, sealing or replacing ductwork
- Diagnosing low refrigerant behind a frozen coil
- Measuring static pressure to confirm a restriction
- Assessing whether a duct run is undersized
The whole-house version of this problem is very often a filter, and that is genuinely yours - do it before you call anyone. The single-room version is almost never the equipment, and the useful thing you bring to the call is the room-by-room map rather than a guess at the cause. Be wary of a replacement quote arrived at without anyone inspecting the ducts.
Is this covered by insurance?
Whether a claim is worth filing depends on the cause, your deductible and how the damage happened - not on the repair price alone.
Sources
Sources last checked
- Heating, Air Conditioning, and Refrigeration Mechanics and Installers - median pay, May 2025U.S. Bureau of Labor Statistics, Occupational Outlook HandbookRetrieved 2026-09-14
- Section 608 Refrigerant Sales RestrictionU.S. Environmental Protection AgencyRetrieved 2026-09-14
Sources for the figures and the legal requirements cited on this page.
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