Unit seems completely dead
No fan sound, no airflow at grilles, and no air at the outside hood.
Start here: Start with power, wall control settings, and any service switch on or near the unit.
Ventilation airflow problem
HRV / ERV Not Exhausting Air
Direct answer: If your HRV or ERV is not exhausting air, the usual causes are a unit that is off or in the wrong mode, packed filters, a blocked exterior hood, or a fan that is running weak or not running at all. Start with the easy airflow checks before you assume the unit needs parts.
Most likely: The most likely problem is restricted airflow at the filters or outside exhaust hood, especially if the unit still has power and you can hear it trying to run.
First figure out whether the unit is completely dead, running but moving very little air, or only failing on the exhaust side. That split matters. Reality check: a lot of 'bad HRV' calls turn out to be neglected filters or a blocked wall cap. Common wrong move: turning fan speed up before checking for a plugged exhaust path.
Don’t start with: Do not start by ordering a motor or control board. On these units, dirty filters, a stuck damper, or an iced or blocked hood waste more time than bad parts do.
If the unit is silent and dead,check the disconnect, breaker, service switch, and wall control before anything else.
If you hear it running but stale air stays in baths or laundry,check filters, the core seating, and the outside exhaust hood for blockage or icing.
Last reviewed: 2026-04-04
What the no-exhaust problem looks like
Unit runs but exhaust is weak
You hear the unit humming or fans spinning, but the outside exhaust flow feels faint and indoor stale air lingers.
Start here: Start with filters, the heat or energy recovery core seating, and the outside exhaust hood.
Supply air seems normal but exhaust is not
Fresh air still comes in, but bathrooms, laundry, or utility areas stay humid or stale.
Start here: Start by checking whether the exhaust side blower is actually spinning and whether the exhaust duct or hood is blocked.
Airflow drops in cold weather
The unit worked better before a cold snap, and now the exterior hood may be frosted or airflow is intermittent.
Start here: Start with the outside hood, screen, and any visible ice buildup before digging into the unit.
Most likely causes
1. Clogged HRV / ERV filters
Loaded filters choke both sides of the unit, and the exhaust side often shows the problem first as weak stale-air removal.
Quick check: Pull the filters and hold them to a light. If they are matted with dust, lint, or grease, airflow is already compromised.
2. Blocked or iced exterior exhaust hood
A bird screen packed with lint, insect nests, leaves, or ice can make the unit sound normal while almost no air leaves the house.
Quick check: Go outside while the unit is on high speed and feel for airflow at the exhaust hood. Look for frost, debris, or a stuck flap.
3. Core installed wrong or not seated fully
After cleaning, the recovery core can go back crooked or backward on some units, which disrupts airflow and can starve one side.
Quick check: Open the access panel and make sure the HRV / ERV core is fully slid into its tracks and the panel closes flat.
4. Exhaust-side blower or control problem
If power is present and the airflow path is clear but only one side is weak or dead, the exhaust blower motor, capacitor if used, or control circuit may be at fault.
Quick check: Listen for one fan running and one fan not, or for a motor that hums, starts slowly, or stops after a few seconds.
Step-by-step fix
Step 1: Confirm the unit is actually being told to run
A surprising number of no-exhaust complaints are just an off control, a timer override, or lost power at the unit.
- Set the wall control to continuous ventilation or high speed, not standby, recirculation-only, or intermittent mode.
- Check the breaker and reset it once if it is tripped. If it trips again, stop there.
- Look for a service switch or unplugged cord at the HRV / ERV cabinet.
- Watch for any indicator lights or display response at the wall control or unit after power is restored.
Next move: If the unit starts and you now have airflow, the problem was power or settings. Keep going to the next steps anyway if airflow still feels weak. If the unit stays dead, the problem is beyond a simple airflow restriction and may be a failed control, transformer, wiring issue, or motor problem.
What to conclude: You need to separate a dead unit from a running-but-restricted unit before anything else.
Stop if:
- The breaker trips again after one reset.
- You smell burning insulation or see scorched wiring.
- The unit has hardwired electrical issues you cannot safely access with power off.
Step 2: Check the outside exhaust hood first
A blocked wall cap is common, visible, and easy to miss from indoors. It can make the whole unit look bad when the real problem is at the outlet.
- Run the unit on high speed for several minutes.
- Go outside and find the exhaust hood, not just the fresh-air intake hood.
- Feel for steady airflow and check whether the flap opens freely.
- Clear leaves, lint, insect nests, or light frost by hand. If needed, use a soft brush and warm water only where it is safe to do so.
- If the hood is packed with solid ice, do not pry hard on plastic parts. Let it thaw gently and find out why it iced over.
Next move: If airflow returns after clearing the hood, you likely solved the main problem. If the hood is clear but airflow is still weak or absent, move inside and check the filters and core.
What to conclude: A clear hood with little or no air points back to the unit, its filters, or the exhaust blower side.
Stop if:
- The hood or duct is damaged and loose at the wall.
- You find heavy ice buildup that keeps returning.
- You cannot safely reach the hood from the ground.
Step 3: Inspect and clean the HRV / ERV filters and core seating
Restricted filters and a misseated core are the most common indoor causes of weak exhaust airflow.
- Turn power off to the unit before opening the access panel.
- Remove the HRV / ERV filters and inspect both sides for dust, lint, pet hair, and greasy buildup.
- Clean reusable filters with mild soap and warm water if the filter type allows it, then let them dry fully before reinstalling. Replace disposable filters if they are loaded or damaged.
- Check that the heat-recovery or energy-recovery core is installed in the correct orientation and fully seated in its tracks.
- Close the access panel firmly so it seals flat. A loose panel can upset airflow and some units will not run properly with it ajar.
Next move: If airflow improves right away, the restriction was inside the cabinet. If the filters are clean, the core is seated correctly, and exhaust is still poor, the next step is to listen for blower-side trouble.
Stop if:
- The core is damaged, torn, or crumbling.
- The cabinet interior is wet enough to drip onto wiring.
- You are unsure how the core orientation goes back together.
Step 4: Listen for one blower side not pulling its weight
When only the exhaust side fails, the unit may still sound alive, but one blower will be slow, noisy, or not spinning at all.
- Restore power and run the unit on high speed with the access panel properly closed unless your unit has a safe service viewing method.
- Listen for uneven fan sound, a hum without full spin-up, scraping, or a fan that starts and stops.
- Check indoor exhaust grilles in bathrooms or utility areas for suction with a tissue. Compare that to airflow at supply grilles if accessible.
- If you can safely view the blower section with power off first and then per the unit's safe access design, look for a wheel that is jammed with debris or rubbing the housing.
- If one side is clearly not moving air while the other side is, note that as an exhaust-side blower or control issue rather than a filter issue.
Next move: If you find and clear a simple obstruction and the blower runs normally after that, recheck airflow at the outside hood and indoor grilles. If one blower still will not run correctly, this is usually a motor, capacitor on applicable designs, or control problem that needs model-specific diagnosis.
Stop if:
- You would need to test live voltage to continue.
- The motor is overheating, smoking, or making sharp grinding noise.
- The blower wheel is damaged or the housing is bent.
Step 5: Finish with a clear next move
Once the simple restrictions are ruled out, guessing gets expensive. The right next move depends on whether you restored airflow or confirmed a component failure.
- If cleaning the hood, filters, or core restored normal exhaust, put the unit back in regular service and monitor it over the next day.
- If the unit runs but airflow is still weak mainly at one area of the house, the problem may be a duct balance or branch restriction rather than the cabinet itself.
- If the unit is powered but the exhaust side blower is clearly dead or intermittent, schedule service or use a model-specific repair procedure for the blower circuit.
- If the unit stays dead after power checks, have the control and wiring diagnosed rather than replacing parts by guesswork.
- If icing, dripping, or heavy condensation is part of the problem, switch to the related condensation issue instead of forcing the unit to run harder.
A good result: You end up with either restored airflow or a much tighter diagnosis before spending money.
If not: If you still cannot confirm where airflow is being lost, professional airflow and electrical testing is the safest next step.
What to conclude: You have narrowed the problem to maintenance, airflow distribution, or a confirmed internal component fault.
Stop if:
- You need to open sealed motor assemblies or perform live electrical testing.
- Condensation is reaching electrical parts.
- The unit is in a location where safe access is poor, such as a high attic or cramped crawlspace.
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FAQ
Why is my HRV or ERV running but not exhausting air?
Most of the time the unit is running against a restriction. Dirty filters, a blocked exterior exhaust hood, or a misseated core are more common than a bad motor. If only one side has weak airflow, then an exhaust-side blower or control issue moves higher on the list.
Can a dirty filter really stop exhaust airflow that much?
Yes. On an HRV or ERV, loaded filters can choke airflow enough that the unit still sounds like it is on but moves very little air. That is why filters are one of the first checks.
How do I tell the intake hood from the exhaust hood?
With the unit running on high, the exhaust hood should push air out and usually open its flap outward. The intake hood pulls air in. Check both, because a blocked intake can also upset overall airflow, but the no-exhaust complaint usually shows up at the exhaust hood first.
Should I keep running the unit if the exhaust hood is iced over?
Not until you know why it iced over. Light frost can happen in cold weather, but heavy recurring ice points to a drainage, defrost, airflow, or balance problem. Forcing the unit to run harder can make the icing worse.
When is it probably a blower motor problem?
After power, settings, filters, core seating, and the outside hood all check out, a one-sided airflow failure strongly suggests the exhaust blower side. A motor that hums, starts slowly, overheats, or never spins is a common clue.
Could the problem be in the ductwork instead of the HRV or ERV unit?
Yes, especially if the unit seems to run normally and the outside hood has decent airflow, but one floor or one room group stays stale. That points more toward a branch duct restriction, disconnected duct, or balancing issue than a dead unit.