Ventilation leak troubleshooting

HRV ERV Condensation Leaking? Check the Drain First

Direct answer: If an HRV or ERV is leaking condensation, start with the drain hose, trap, cabinet pitch, and dirty filters before you price a core or motor.

Most likely: First prove the water starts at the cabinet drain. Wet duct insulation, sweating collars, and a sagged hose can all leave the same puddle.

Dry the area, watch where fresh moisture appears, then choose the next check from the water path.

Don’t start with: Do not open sealed sections, run the unit with wet wiring nearby, or blow compressed air backward through the drain.

Cabinet bottom is wet firstPower off, then inspect the hose, trap, and cabinet pitch.

Cold duct or collar beads firstTreat it as duct sweating or air leakage before buying unit parts.

Do this first

Turn the HRV or ERV off at its service switch or breaker before opening access panels or touching the drain hose.
Stop if water is reaching wiring, controls, a receptacle, a junction box, or any nearby electrical equipment.
Do not work from an unstable ladder or one-handed reach on a ceiling-hung unit.
Do not spray cleaner, compressed air, or rinse water into the cabinet, motor area, core, or control compartment.
Keep the unit off and call for service if you see heavy frost, a dead fan, hot odor, scorch marks, a tripped breaker, or soaked finishes you cannot fully dry.

Last reviewed: 2026-04-04

Fast leak sorter

Is the cabinet bottom wet first?

Work on the condensate path first. Start at the drain outlet, hose slope, trap water, and cabinet pitch with power off.

Is the duct jacket or collar wet first?

Treat it as duct sweating or air leakage. Look for torn insulation, loose vapor jacket, cold metal, or humid room air hitting the duct.

Does the hose have a sag, kink, or slime?

Clear the accessible hose with warm water, remove the low pocket, and refill the trap if your unit uses one.

Does the leak show up only in cold weather?

Look for restricted filters, blocked outdoor hoods, frost in the accessible core area, and a drain line that lets water sit long enough to freeze.

Is the unit tilted away from the drain?

A small pitch can hold water in the wrong corner. Adjust only if the mounting is safe and you can support the unit.

Is there wet wiring, heavy ice, or a dead fan?

Stop the DIY checks and schedule HVAC service. Those clues are beyond a simple drain clean or filter change.

Where the HRV or ERV leak usually starts

Use the first wet spot to separate a cabinet drain problem from duct sweating. Dry the area, run the unit only if it is safe, and watch where new moisture forms.

HRV or ERV cabinet with condensate drain hose and wet towel below — Start with the cabinet drain area and nearby duct collars. The first fresh moisture tells you whether to work on drainage or duct sweating.

Sagging HRV or ERV condensate hose holding water below cabinet drain — A sag, kink, or dry trap can hold water until it backs into the cabinet. Clear the hose gently with power off.

Sweating HRV or ERV duct collar dripping while cabinet drain stays dry — Water beads on the duct collar point you away from the cabinet drain. Fix insulation, vapor jacket, and air leaks before ordering unit parts.

Before you buy anything

Do not buy a core, fan motor, trap kit, or drain hose until the water path points there. Prove the first wet spot, clear the existing hose if it comes apart safely, check filter condition, and match any replacement to the exact HRV or ERV model and drain size.

Jump to: First wet spot results · Tools You May Need · Replacement Parts

What is probably happening

An HRV or ERV can make normal condensate. That water needs a clear drain path. A little blockage, dry trap, hose sag, or low airflow can make it pool inside.

A steady drip below the cabinet usually points to the drain outlet, hose, trap, or cabinet pitch.
Water beads on a duct jacket or metal collar usually point to cold ductwork meeting humid room air.
A winter-only leak moves frost, dirty filters, blocked outdoor hoods, and slow drainage up the list.
A leak after a filter change or panel removal can be as simple as a panel not seated or a hose bumped out of slope.
Stop if water reaches wiring, a fan will not run, or heavy frost returns after clean filters. Those clues need HVAC service before parts.

What not to do first

The expensive shortcuts are the wrong first move on this symptom. Keep the early checks low-risk: power off, dry the area, follow the water, and avoid pushing debris back into the cabinet.

Do not open sealed sections or electrical compartments to chase a leak you have not traced yet.
Do not blow compressed air backward through the drain unless you know where the water and debris will go.
Do not pour bleach, drain cleaner, or foaming cleaner into the HRV or ERV cabinet.
Do not wrap wet duct insulation and call it fixed. The moisture source has to be corrected first.
Trace the first wet spot, hose slope, trap water, filter condition, and frost pattern before pricing a core, fan, control board, or trap kit.
Do not keep running the unit if water is reaching wiring, drywall, insulation, or a finished ceiling.

First wet spot results

Dry the cabinet, hose, duct collars, and floor. If the unit can be run safely without touching moving parts or wiring, watch one short cycle and use the first new moisture as the clue.

Use a flashlight at the drain outlet, cabinet bottom, first duct collars, and any insulated duct jacket nearby.
Look for mineral trails, rusty streaks, dust paths, or a drip that starts before the floor puddle spreads.
If the unit is overhead, stay on a stable platform and stop if you cannot see the drain without reaching awkwardly.

What gets wet first	What it usually means	Next check
Drain outlet or hose	Blocked hose, bad trap, low pocket, or cracked connection.	Power off, inspect the hose and trap, and catch water before disconnecting anything.
Cabinet bottom or side seam	Water is pooling inside before it reaches the drain.	Check drain flow, cabinet pitch, and accessible frost or overflow marks.
Duct collar or insulation jacket	Sweating duct, loose vapor jacket, or air leak at the connection.	Repair insulation and air sealing before buying HRV or ERV parts.
Core area or filter area	Restricted airflow, frost, or a panel that is not seated.	Clean or replace filters and stop for heavy ice or fan trouble.
Wiring, control area, or receptacle	Electrical wetting risk.	Leave power off and call an HVAC tech or electrician as appropriate.

Clear the drain path without forcing it

The drain hose is the first real repair check because it is common, visible, and usually safer than opening deeper cabinet sections. Work with power off and keep water away from the unit.

Follow the hose from the cabinet outlet to the drain point and look for slime, sediment, kinks, pinches, or a low belly full of water.
Disconnect only sections that are meant to come apart and only where you can catch the water in a container or towels.
Flush the removed hose or trap with warm water away from the cabinet until water runs freely.
Refill the trap with water before reconnecting if your model uses a trap.
Set the hose back in a steady downhill run after the trap, without a sag that can hold standing water.
Stop if the cabinet drain nipple is cracked, brittle, loose, or tied into plumbing you are not comfortable opening.

Check pitch, filters, and frost clues

If the drain is open but water still appears at the cabinet, look for clues that make condensate outrun the drain: pitch, airflow, and frost.

Set a small level on a flat cabinet surface if you can reach it safely. Water should not be held in a corner away from the drain.
Open only normal service panels with power off, then look for standing water, mineral marks, or one damp corner inside.
Pull the filters and check for dust matting, damp debris, pet hair, or a filter installed crooked.
Clean washable filters only if the unit manual allows it and let them dry before reinstalling.
Replace disposable or damaged filters with the exact size and style for the model.
Stop for solid ice, repeated frost after clean filters, a fan that does not run, or any live electrical testing.

When duct sweating is the real leak

A lot of HRV and ERV leak calls start beside the unit, not inside it. Cold fresh-air duct, damaged insulation, or a loose vapor jacket can drip onto the same floor area.

Wipe the cabinet and duct dry, then watch whether new water beads on the duct jacket or metal collar before the drain area gets wet.
Feel for moving air at duct seams and collars while the unit runs, but keep hands clear of open panels and wiring.
Look for torn foil jacket, compressed insulation, missing tape, dark dust streaks, or cold exposed metal.
Do not cover soaked insulation with new wrap. Remove wet material where needed and let the area dry.
If duct sweating is widespread, check indoor humidity and ask an HVAC tech to review insulation, air sealing, and system setup.

Tools You May Need

These tools support the safe homeowner checks. Skip any tool that would push you into wet wiring, unstable access, or disassembly beyond normal service panels.

Inspection flashlight

Helps when: Tracks mineral streaks, water beads, frost, and the first wet spot under or beside the cabinet.

Skip it when: Water is touching wiring or the unit is too high to inspect from a stable platform.

Compare inspection flashlights on Amazon

Small catch pan or container

Helps when: Catches water when an accessible drain hose or trap section is disconnected for a warm-water flush.

Skip it when: The drain ties into plumbing or the cabinet fitting looks cracked, brittle, or loose.

Compare small catch pans on Amazon

Small torpedo level

Helps when: Checks whether the HRV or ERV cabinet is pitched in a way that holds water away from the drain.

Skip it when: The unit is ceiling-hung or would need unsupported mounting adjustments to change pitch.

Compare small levels on Amazon

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Replacement Parts

Buy parts only after the check points to them. Match the exact HRV or ERV model, drain size, filter dimensions, and manufacturer style before ordering.

HRV or ERV replacement filter

Helps when: The old filter is disposable, damaged, packed with dust, or airflow improves after you remove it for inspection.

Skip it when: The filter is clean and the leak starts at the drain hose, duct collar, wiring area, or internal frost.

Compare HRV and ERV filters on Amazon

Flexible condensate drain tubing

Helps when: The existing tubing is kinked, cracked, slimed inside, or permanently sagged and matches the same diameter and routing.

Skip it when: The cabinet drain fitting is cracked or the tubing size, trap layout, or termination point is uncertain.

Compare condensate drain tubing on Amazon

HRV or ERV condensate trap and hose area checked before buying a trap kit

HRV or ERV condensate trap kit

Helps when: The original trap is missing, cracked, or will not hold water, and the unit manual calls for that trap style.

Skip it when: You have not proved the trap is the issue or the drain ties into plumbing you should not alter.

Compare condensate trap kits on Amazon

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FAQ

Why does my HRV or ERV leak only in winter?

Cold weather makes frost and condensate problems show up faster. Look at the drain hose, trap, filters, outdoor hoods, and any frost around the accessible core area before you blame an internal part.

Can a dirty HRV or ERV filter really cause a water leak?

Yes, it can contribute. A loaded filter cuts airflow, which can make the cold side frost harder and shed more meltwater than the drain is handling well.

Is water under the unit always coming from inside the HRV or ERV?

No. A cold duct collar, torn vapor jacket, or wet insulation can drip near the cabinet and look like a unit leak. Dry both areas and watch where fresh moisture appears first.

Should I pour bleach or drain cleaner into the HRV or ERV drain line?

No. Harsh chemicals can damage tubing, seals, or nearby components. Use warm water on a disconnected hose section when you can catch the water safely.

Can I keep running an HRV or ERV that is leaking water?

Leave it off if water is near wiring, controls, a receptacle, or finished surfaces that are getting soaked. A small drain drip can become electrical trouble or building damage if it keeps running.

Should the HRV or ERV condensate trap have water in it?

If your unit uses a trap, check that the trap is installed, routed correctly, and holding water before the next run cycle. A dry, cracked, or missing trap can leave condensate sitting near the cabinet drain.

Should I replace the HRV or ERV core if it leaks?

No, not from the puddle alone. First trace the drain hose, trap, cabinet pitch, filter condition, frost, and duct sweating. Price a core only after those checks or an HVAC tech point there.

When should I call an HVAC tech for an HRV or ERV condensation leak?

Call for service when the drain is clear, the trap is right, the cabinet is level, filters are clean, and water still returns. Also call for repeated frost, a dead fan, wet wiring, or hidden water damage.

How this guide was built

Repair Riot built this page around safe homeowner checks: first wet spot, condensate drain path, trap behavior, cabinet pitch, filters, frost, and duct sweating. The source links support the ventilation, frost-protection, maintenance, and duct-insulation context; the repair sequence is original guidance.

DOE Energy Saver whole-house ventilation — supports HRV and ERV basics, cold-climate frost protection, maintenance needs, and duct insulation context.
DOE Energy Saver duct energy losses — supports checking duct sealing, insulation, airflow restrictions, and vapor-barrier issues when moisture appears on ductwork.