Air exchanger maintenance: filters, core and winter care

In a well-sealed house, the air exchanger brings in fresh air. In winter, a model with heat recovery (HRV) captures the heat of the stale air it exhausts and uses it to preheat the fresh air coming in. According to Natural Resources Canada, an HRV typically recovers 70 to 80 percent of the heat from the exhaust air. That is, as long as it is maintained.

1. Keep it running

Hydro-Québec recommends making sure the air exchanger runs at all times and never turning it off except for maintenance. The unit helps remove excess humidity, household chemicals and other indoor air pollutants. If you are replacing yours, Hydro-Québec suggests a model with heat recovery and ENERGY STAR certification, which offers better performance.

2. Maintenance in 7 steps

Canada Mortgage and Housing Corporation (CMHC) suggests seven simple steps. Keep the manufacturer’s manual for your unit handy.

1. Turn the unit off and unplug it before any maintenance, for your safety.
2. Clean or replace the filters. Dirty filters lower ventilation efficiency. CMHC advises doing it every 2 months; Hydro-Québec says at least every 3 months. On newer units the filters come out easily and can be vacuumed and washed with mild soap and water; older units have replaceable filters.
3. Check the outdoor intake and exhaust hoods. Remove leaves and debris. In winter, remove the snow or frost blocking them: the unit won’t work properly if they are blocked. A hood close to the ground or under a balcony fills up quickly after a snowfall.
4. Check the condensate drain. If the unit has one (a small plastic tube at the bottom), slowly pour about 2 litres of warm, clean water into each drain pan. If the water backs up, clean the drain until it flows freely.
5. Clean the core. Follow the manufacturer’s manual: vacuum the core and wash it with water and mild soap to reduce dust build-up.
6. Clean the grilles and check the ducts once a year: remove the grilles at the duct ends and vacuum inside. For a deeper cleaning, call a service technician.
7. Check the fans. Gently brush the dust off the blades. Most new units run without lubrication; an older one may need a few drops of motor oil in the designated opening, as the manual explains.

3. Too humid or too dry?

Occasional condensation is not a problem. According to Natural Resources Canada, heavy condensation or frost on the windows means you should reduce the moisture produced in the house or increase ventilation: first check that the exchanger is running and that its filters and hoods are clean. The humidity level to aim for and how to cut condensation are in our guide on mould and humidity.

On the other hand, air that is too dry in winter can come from over-ventilation: the system may be oversized or need to be slowed down. An energy recovery ventilator (ERV), which also transfers some moisture, can help keep a more comfortable humidity level when the house produces little moisture.

4. Humidity in a Montréal rental: what the City expects

In a Montréal plex, ventilation is often what tenants and landlords disagree about in winter. The City’s page Tenants: you have the right to a dwelling in good condition (in French, updated December 19, 2025) says the dwelling must meet the standards of By-law 03-096 and be free of mould. It asks occupants to keep surfaces dry, run the range hood while cooking and the bathroom fan, and, where there is no mechanical ventilation, to air the place out for a few minutes, even in winter. If the landlord does not act within a reasonable time, the tenant can contact the City and ask for an inspection.

For owners of a building with 2 to 5 dwellings, the City’s RénoPlex program (in French, updated June 19, 2026) lists ventilation among the work covered by its second component, subject to a property value condition and to waiting for the application to be accepted before starting.

5. When to call a company

• For a thorough duct cleaning, or if water still backs up after you clean the drain.
• If the unit makes an unusual noise, won’t start, or condensation problems persist despite maintenance.
• To install or replace a system: Natural Resources Canada says a central ventilation system should be designed and installed by a professional, with balanced supply and exhaust air flows so the house pressure is not affected.

In Quebec, residential ventilation work falls under RBQ subclass 15.7 (residential ventilation) or 15.8 (ventilation); look up the licence and get the model, ductwork and balancing in writing. Ventilation companies work in Mercier–Hochelaga-Maisonneuve, Pointe-Claire and Mascouche, and the form lets you request air exchanger service or a replacement.