Why Is My HRV Not Working Properly? Common Air Exchanger Problems
Why Is My HRV Not Working Properly? Common Air Exchanger Problems
Last updated: September 28, 2026
An HRV that stops doing its job rarely stops outright — it fades. The windows fog a little more each week, the house feels stuffier, the unit sounds different. Because the decline is gradual, many Nova Scotia homeowners adapt to poor ventilation without realizing their air exchanger has a fixable problem.
Here are the most common HRV and air exchanger problems we see, what causes them, what you can check yourself, and when to book a professional.
Problem 1: Condensation on Windows Despite the HRV Running
What is happening: Your HRV's job includes exhausting the moist indoor air that fogs windows. If condensation is back, the system is not moving enough air — usually because clogged filters or a dust-matted core have throttled airflow, or because the system has drifted out of balance (exhausting less than it supplies, or vice versa).
What to check: Pull the filters. If they are grey and matted, wash or vacuum them and see whether the fogging improves over the next few days. If filters were fine or cleaning them changes nothing, the core or balance needs professional attention [1].
Problem 2: Weak or No Airflow From the Vents
What is happening: The progression is filters first, then the core, then the fan motors. A severely clogged core can reduce airflow to a trickle even with clean filters. Less commonly, a failed motor or a disconnected duct is the cause.
What to check: Filters, then the exterior hoods — a blocked intake hood (leaves, snow, a nest) starves the whole system. Beyond that, airflow needs to be measured at the unit to isolate the restriction, which is part of a professional service.
Problem 3: Water Leaking From the Unit
What is happening: HRVs produce condensate in winter, and it drains through a small line at the bottom of the unit. When biofilm or debris blocks that drain, water backs up and leaks from the casing. A related winter problem is a core that has frosted over (see problem 5) and is now melting into a pan that cannot drain.
What to check: Look for the drain line and confirm it is connected and unobstructed at the exit. If the line is clear where you can see it but leaking continues, the blockage is internal and needs a flush.
[NORDAIR PHOTO — blocked condensate drain or leaking unit from a real service call, filename: hrv-condensate-drain-blockage-leak.webp]
Problem 4: New Noises — Rattling, Humming, or Whining
What is happening: Rattling usually means debris in a fan or a loose panel. A louder-than-usual hum indicates motors straining against restricted airflow. Whining or grinding points to worn motor bearings — the one problem on this list that cleaning alone will not fix.
What to check: Confirm panels are seated and filters are properly installed. If the noise persists, book service before a straining motor becomes a dead motor.
Problem 5: Frost Buildup and Defrost Problems in Deep Cold
What is happening: In extreme cold, moisture in the exhaust stream can frost the core. HRVs have a defrost cycle to manage this, but a dirty core frosts faster and a malfunctioning defrost lets ice accumulate until airflow stops entirely. If your HRV seems to quit during cold snaps and recover when it warms up, this is the likely story. Our article on HRV condensation problems [blocked] covers the moisture side of winter operation in more detail.
What to check: Nothing internal — but note the pattern (cold-snap failure, warm-up recovery) for the technician, because it points directly at the defrost system and core condition.
Problem 6: Stale Air and Lingering Odours
What is happening: If cooking smells hang around for hours and the house feels stuffy despite the HRV running, ventilation rates have dropped below what your household produces. The causes are the usual suspects — filters, core, balance — but so is an undersized or misconfigured system, which is worth identifying.
The Common Denominator
Look down that list and a pattern emerges: most HRV problems are maintenance problems. Filters, core, drain, balance — the four things a professional cleaning and inspection addresses are the four things behind the majority of complaints. Systems on a regular schedule rarely develop these issues; systems cleaned "a few years ago, maybe" almost always do. Our guides on how often your HRV should be cleaned [blocked] and the complete guide to HRV and ERV cleaning [blocked] lay out the schedule and the service.
[NORDAIR FIELD NOTE — insert 1–2 sentences of real technician observation here, e.g., the most common HRV complaint the team receives and what usually turns out to be the cause.]
Frequently Asked Questions
Why are my windows fogging up if my HRV is running?
Running is not the same as ventilating. Clogged filters, a dirty core, or an unbalanced system can cut airflow to the point where moist indoor air is no longer exhausted effectively. Start with the filters; if fogging persists, book a service.
Why is my HRV so loud all of a sudden?
A louder hum usually means the motors are straining against restricted airflow — clean the filters first. Rattling suggests debris or a loose panel. Grinding or whining points to worn bearings, which is a repair rather than a cleaning issue.
Why is water leaking from my HRV?
Almost always a blocked condensate drain. The unit produces water in winter, and when the drain clogs with biofilm, the water backs up and escapes through the casing. A professional drain flush resolves it.
What does it mean when my HRV freezes up in winter?
Core frosting happens in extreme cold and is managed by the unit's defrost cycle. Frequent freeze-ups mean the core is dirty (frosting faster than the defrost can manage) or the defrost system has a fault. Either way, it needs service.
Can I troubleshoot my HRV myself before calling?
Yes — check and wash the filters, clear the exterior hoods, confirm the drain line is connected, and note exactly when symptoms occur. That covers the DIY-safe checks and gives the technician useful information if the problem persists.
When is an HRV problem a replacement problem?
Age and motor condition decide. If the unit is 15–20 years old, needs a motor, and has a damaged core, replacement often beats repair. Most problems on newer units, though, are resolved by cleaning and balancing at a fraction of replacement cost.
HRV acting up? NordAir Atlantic's air exchanger cleaning service [blocked] includes core deep cleaning, drain flushing, and airflow verification, starting at $179. Call (902) 903-0772 or book an HRV inspection [blocked].
References
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