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Ventilation matters because Canadian houses have become much more airtight, which saves energy but can leave the air stale. Natural Resources Canada notes that modern homes use HRVs to distribute fresh air, and that an HRV also gets rid of many indoor pollutants, such as excess moisture, household chemicals and bacteria.
An air exchanger only works well if it is maintained and balanced. This page compares HRVs and ERVs, lists the signs of poor ventilation, walks through filter, core, drain and hood maintenance, explains balancing, winter humidity and radon, and covers adding a unit during a renovation.
HRV or ERV: choosing between heat recovery and energy recovery ventilators
Both types bring in outdoor air and exhaust stale air in the same way; the difference is in the core. An HRV transfers heat between the two airstreams, while Natural Resources Canada describes an ERV as a type of HRV that can exchange both heat and moisture. In warm, humid weather, an ERV gives you more control by keeping some of the outdoor moisture out of the house.
The right choice depends on how many people live in the home, how much moisture it produces, whether it tends to be too dry or too damp in winter, and the local climate. There's no universal answer, so ask a qualified ventilation contractor to size and recommend the unit, and look for an ENERGY STAR certified model, which Natural Resources Canada says uses less energy, on average, than a standard one.
Signs your home needs better ventilation or an air exchanger check
A tight house without enough fresh air tends to show it, and so does an HRV or ERV that has been switched off, left with clogged filters or never balanced. Natural Resources Canada advises never turning an HRV or ERV off except for servicing, since it is designed to run all the time.
- Heavy condensation or frost on the inside of the windows in winter.
- Cooking odours, stuffiness or stale air that linger for hours.
- Musty smells or mould spots in closets, in corners or on window frames.
- Humidity readings that stay above the range Health Canada recommends.
- A unit that is noisy, rattles or has stopped running, or a control showing a filter or fault alert.
- Cold drafts from the supply grilles in winter, which can point to a core, defrost or balancing problem.
HRV and ERV maintenance: filters, core, condensate drain and exterior hoods
Natural Resources Canada says routine maintenance is usually within a homeowner's reach: cleaning the filters and the core and checking components as the service manual describes. CMHC suggests cleaning or replacing HRV filters every two months, and Natural Resources Canada's ENERGY STAR guidance gives a range of one to three months, so your own manual sets the exact schedule. Turn the unit off and unplug it before opening the access door.
- Filters: vacuum washable filters and wash them in mild soapy water, as CMHC describes, or replace disposable ones, and let washed filters dry before putting them back.
- Core: slide it out and vacuum it, then wash it with soap and water if the manual allows, which CMHC says reduces the dust that builds up inside; some ERV cores must not be washed, so check first.
- Condensate drain: if your unit has one, CMHC suggests slowly pouring about 2 litres of warm, clean water into each drain pan and cleaning the drain until the water flows freely.
- Fans: gently brush off the dirt that collects on the blades, as CMHC recommends.
- Exterior hoods: remove leaves, paper and other debris, and clear away any snow or frost blocking the intake or the exhaust.
- Call a technician when the core or fans need a more thorough cleaning, or when airflow stays weak even with clean filters.
Balancing an HRV or ERV: why a qualified technician should do it
Balancing means adjusting the unit so it brings in about as much air as it exhausts. The technician measures the airflow in the fresh-air and stale-air ducts with instruments, then sets the dampers and fan speeds to match the design. An unbalanced unit can push humid indoor air into the walls and attic, or put the house under negative pressure, which draws in cold drafts and can interfere with the venting of fuel-burning appliances such as a furnace, a water heater or a fireplace.
Balancing belongs at installation and commissioning, and again after changes to the ductwork, a new furnace or a major renovation. Keep the balancing report with the manual, since it records the airflows the next technician should expect to find.
Winter humidity and your air exchanger: keeping indoor air between 30% and 50%
Health Canada recommends keeping indoor relative humidity between 30% and 50%, and a simple hygrometer shows where your home stands. In the heating season, an HRV removes moisture along with stale air, which helps a house that suffers from window condensation. In a small or lightly occupied home during a cold snap, the same effect can make the air too dry. Many controls offer several speeds or a humidity setting, so adjust those within the manufacturer's guidance rather than switching the unit off. An ERV keeps part of the indoor moisture, one reason some homes that run dry in winter use one.
In very cold weather the unit runs a defrost cycle from time to time to keep the core from freezing, which is normal. Ice building up inside the cabinet, in the drain or on the exterior hoods is not, and calls for a service visit.
- Condensation running down the windows usually means humidity is too high, so raise the ventilation rate and check that bathroom and kitchen fans work.
- Dry skin, static shocks and cracking wood trim can mean the air is too dry, so lower the ventilation speed or the humidity setting as the manual allows.
- Keep window coverings open enough to let warm air reach the glass, as Health Canada suggests.
- Keep the exterior hoods clear of snow, frost and ice all winter long.
Adding an HRV or ERV during a renovation: installation options
Renovations that add insulation, new windows or air sealing make a house tighter, which makes them the right moment to plan mechanical ventilation instead of treating it as an afterthought. Natural Resources Canada suggests consulting a local accredited HVAC contractor to choose the right system, and an energy advisor can also help assess how much fresh air the home needs and where the unit, ducts and hoods can go.
- Fully ducted system: dedicated ducts bring fresh air to bedrooms and living areas and draw stale air from bathrooms, which is easiest while walls and ceilings are open.
- Simplified system: the unit connects to the furnace ductwork to distribute fresh air, which needs careful design so the two systems work together.
- Exterior hoods placed apart from each other and away from the dryer vent, the furnace exhaust and the driveway, so the fresh air stays clean.
- A route for the condensate drain, a power outlet and enough room to open the unit, all planned before the walls are closed.
- A contractor with ventilation training and the licence your province requires, who hands over a balancing report at the end of the job.
HRV & ERV Systems: frequently asked questions
Should an HRV run all the time?
In most homes, yes. Natural Resources Canada advises never turning an HRV or ERV off except for servicing. If the air feels too dry or too damp, adjust the speed or the humidity setting instead.
Can an HRV reduce radon?
It can help, but it isn't a cure. Health Canada's radon reduction guide says an HRV brings in outdoor air, which might reduce radon by 25 to 50 per cent in most homes, while active sub-slab depressurization remains the most effective method. Use a long-term test to check the level before and after any change.
What's the difference between an HRV and a bathroom fan?
A bathroom fan only exhausts air from one room. An HRV or ERV exhausts stale air and supplies fresh air at the same time, recovering heat along the way, so the house stays balanced. Bathroom fans and range hoods still matter for removing moisture and odours quickly where they are produced.
Why is my HRV blowing cold air?
Supply air that feels a little cool in winter is normal, because the incoming air is warmed by the core, not heated like furnace air. Air much colder than usual can mean a dirty or frozen core, a defrost problem or unbalanced airflow. Clean the filters and core, check the hoods, and call a technician if it continues.
Does an older house need an air exchanger?
Not always. An older, leakier house gets some air through gaps, but that air is uncontrolled and uneven. If you tighten the house with insulation, new windows or air sealing, plan ventilation as part of the project and have a qualified contractor assess it.
Sources
- Natural Resources Canada: Heat and energy recovery ventilators (ENERGY STAR)
- Natural Resources Canada: What's a heat/energy recovery ventilator and why do I need one?
- Natural Resources Canada: Keeping the Heat In, section 9, operating your house
- CMHC: How to maintain a heat recovery ventilator
- Health Canada: Guide to addressing moisture and mould indoors
- Health Canada: Radon, a reduction guide for Canadians
Written by the LokalMatch editorial team. Reviewed by Zubair Afzal on September 10, 2026. How we write and check our guides