Puddle directly under the cabinet
The floor or platform gets wet below the unit, usually during cold weather or longer run times.
Start here: Start with the drain outlet, trap, hose routing, and whether the unit is sitting level.
Ventilation leak troubleshooting
HRV ERV Condensation Leaking
Direct answer: Most HRV and ERV condensation leaks come from a blocked drain line, a dry or missing trap, a unit that is out of level, or restricted airflow that lets water collect where it should be draining away.
Most likely: Start by confirming the water is actually coming from the HRV or ERV cabinet and drain connection, not from sweating ductwork nearby. Then check the condensate drain hose, trap, and filters before assuming an internal part failed.
When these units leak, the pattern matters. A steady drip under the cabinet points you one way. Water beading on insulated duct or dripping from a collar points another way. Reality check: a lot of 'unit leaks' turn out to be duct condensation or a sagged drain hose. Common wrong move: blowing compressed air into the drain without checking where the blockage will go, which can push water and debris back into the cabinet.
Don’t start with: Do not start by opening sealed sections, replacing motors, or buying a new core. On these units, water problems are usually drainage or airflow first.
Water under the unit only when it runsCheck the drain hose, trap, and cabinet level first.
Water on the outside of nearby ductTreat that as a duct sweating problem before blaming the HRV or ERV itself.
Last reviewed: 2026-04-04
Figure out where the water is starting before you touch parts
Water dripping from a side panel or seam
You see water tracking down the cabinet instead of coming cleanly from the drain connection.
Start here: Look for a blocked drain path, internal water pooling, or a cabinet that is pitched the wrong way.
Water at the duct connection
The leak shows up around a collar, insulated flex, or metal duct near the unit.
Start here: Check for sweating duct, missing insulation, or very cold surfaces meeting humid room air.
Leak only in very cold weather
The unit seems fine most days, then starts dripping during freezing or near-freezing conditions.
Start here: Check for partial drain blockage, ice buildup, restricted filters, or airflow problems that let frost and meltwater overwhelm the drain.
Most likely causes
1. Blocked or partially blocked HRV/ERV condensate drain line
This is the most common cause when water collects in the cabinet and then spills out the bottom or a seam.
Quick check: With power off, inspect the drain hose for slime, debris, kinks, sags, or a low spot full of water.
2. Dry, missing, or misrouted HRV/ERV condensate trap
If the trap is wrong or empty, air can interfere with drainage and let water sit in the pan area instead of flowing out.
Quick check: Look for a proper trap near the drain outlet and check whether it actually contains water.
3. Restricted airflow from dirty HRV/ERV filters or a frosted core area
Low airflow can let the unit run colder than it should, build frost, and then dump excess meltwater during defrost or warmer cycles.
Quick check: Pull the filters and inspect for heavy dust loading, damp buildup, or obvious frost inside accessible areas.
4. Condensation on nearby ductwork, not a true cabinet leak
Cold fresh-air duct or poorly insulated collars often sweat and drip in a way that looks like the unit is leaking.
Quick check: Wipe the cabinet dry, then watch whether new moisture forms first on the duct jacket, metal collar, or cabinet drain area.
Step-by-step fix
Step 1: Pinpoint the first wet spot
You need to separate a real cabinet leak from sweating duct or water tracking along framing. That saves a lot of wrong repairs.
- Turn the unit off at its service switch or breaker before opening access panels.
- Dry the cabinet, drain connection, nearby duct, and the floor below with towels.
- Look for water staining, mineral tracks, rust marks, or dirt trails that show the usual path.
- Check whether the first moisture appears at the drain outlet, under the cabinet, or on the outside of a duct connection.
- If the leak is only happening while the unit runs, restart it briefly and watch with the access area open only if you can do that safely without reaching into moving parts or wiring.
Next move: If you clearly see the water starting on the outside of ductwork, you are dealing with condensation on the duct, not a failed internal unit part. If you still cannot tell where it starts, move to the drain checks next because that is still the highest-probability cause.
What to conclude: The location of the first wet spot tells you whether to focus on drainage inside the HRV/ERV or sweating surfaces outside it.
Stop if:
- Water is reaching electrical wiring, controls, or a nearby receptacle.
- You see heavy ice buildup inside the unit.
- You cannot access the unit safely from a stable platform or ladder.
Step 2: Check the HRV/ERV drain hose and trap
A blocked hose or bad trap is the most common reason condensate backs up and spills out of the cabinet.
- Leave power off.
- Follow the condensate hose from the HRV/ERV drain outlet to its termination point.
- Straighten any sharp kinks and correct any sag that creates a water pocket in the hose.
- Disconnect the hose only if you can catch the water safely in a container or towel.
- Flush the hose with warm water until it runs freely. If there is a trap, clean it and refill it with water before reconnecting.
- Make sure the hose slopes continuously downward after the trap and is not pinched where it passes through framing or beside the unit.
Next move: If water drains freely and the leak stops on the next run cycle, the problem was a blocked or poorly routed drain path. If the hose is clear and the trap is correct but water still leaks, check cabinet level and airflow next.
What to conclude: A clear, properly trapped drain should let normal condensate leave the unit without pooling inside.
Stop if:
- The drain connection is cracked at the cabinet and feels brittle or loose.
- You find hidden water damage inside a wall or ceiling cavity.
- The drain ties into plumbing in a way you are not comfortable disconnecting.
Step 3: Check cabinet level and look for internal pooling
These units do not tolerate being pitched the wrong way. A slight tilt can leave water sitting in the wrong corner until it spills out.
- Set a small level on the top of the HRV/ERV cabinet if the top is accessible and reasonably flat.
- Compare side-to-side and front-to-back level.
- Look inside the accessible service area for standing water, water marks, or one corner that stays wetter than the rest.
- If the unit is obviously out of level and the mounting method allows a simple adjustment, correct the pitch carefully so water drains toward the outlet.
- Reinstall the panel and run the unit long enough to see whether the leak pattern changes.
Next move: If the leak stops after correcting the pitch, the unit was holding water instead of draining it. If the unit is level and still leaking, restricted airflow or frost buildup is more likely.
Stop if:
- The unit is ceiling-hung and adjustment would require loosening suspension hardware you cannot safely support.
- The cabinet mounting is damaged, rusted through, or pulling away from framing.
- You see water near internal wiring or control boards.
Step 4: Inspect the HRV/ERV filters and accessible core area
Dirty filters and low airflow can let the unit run too cold, build frost, and then leak when that frost melts.
- Turn power off again and remove the access panel.
- Pull the HRV/ERV filters and inspect for heavy dust, matting, or damp debris.
- Clean reusable filters only if the unit uses washable filters and they are in good shape; otherwise replace them with the correct type and size.
- Look into the accessible core area for frost, ice residue, or signs that water has been overflowing during defrost.
- Reinstall everything securely so panels seal properly, then run the unit and watch for improved drainage.
Next move: If airflow improves and the leaking stops after filter service, the unit was likely holding excess moisture because of restricted airflow. If filters are clean and you still see frost, repeated icing, or ongoing leakage, the unit needs deeper diagnosis for defrost, fan, or control problems.
Step 5: Finish with the right next move
At this point you should know whether this is a simple drain or filter issue, a duct sweating issue, or a higher-risk internal problem.
- If the leak stopped after clearing the drain or correcting hose routing, keep the unit running and recheck over the next day for any new drips.
- If the leak stopped after filter service, note the filter size and replacement interval so airflow does not fall off again.
- If the cabinet stays dry but nearby duct still sweats, shift your attention to insulation, air sealing, and room humidity around that duct run.
- If the unit still leaks with a clear drain, proper trap, correct pitch, and clean filters, schedule HVAC service for internal frost, fan, or control diagnosis.
- If water has reached wiring, insulation, drywall, or finished surfaces, dry the area promptly and address the damage before mold or staining sets in.
A good result: If the unit stays dry through several run cycles, you have likely solved the problem without replacing major components.
If not: If leaking returns in cold weather or during long run times, the unit likely has an internal airflow or defrost issue that is not a good guess-and-buy repair.
What to conclude: Simple drainage and filter problems are homeowner territory. Persistent leaking after those checks usually is not.
Stop if:
- The leak returns immediately after basic drain and filter service.
- You see recurring frost with clean filters and normal drain flow.
- Any repair would require live electrical testing or disassembly beyond normal service panels.
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FAQ
Why does my HRV or ERV leak only in winter?
Cold-weather operation creates the most condensate and is when partial drain blockages, bad traps, and frost-related overflow show up. If it only happens in winter, check the drain path, trap, filters, and any sign of icing first.
Can a dirty filter really make an HRV or ERV leak water?
Yes. Restricted airflow can let the unit run colder, build frost, and then shed more meltwater than the drain is handling well. A dirty filter is not the only cause, but it is common and easy to rule out.
Is water around the unit always coming from inside the HRV or ERV?
No. Sweating ductwork is a frequent lookalike. If the outside of a cold duct or collar is wet first, the unit may be fine and the real problem is insulation, air leakage, or high room humidity around that duct.
Should I pour bleach or drain cleaner into the HRV or ERV drain line?
No. Harsh chemicals can damage tubing, seals, or nearby components. Start with warm water and a simple flush after disconnecting the hose safely. If the blockage will not clear, it is better to stop than force debris back into the unit.
When should I call a pro for an HRV or ERV leak?
Call for service if the drain is clear, the trap is correct, the unit is level, filters are clean, and it still leaks. Also call if you see repeated frost, a non-running fan, electrical wetting, or damage to surrounding finishes.