HRVs and ERVs: fresh air that keeps most of the heat

How an HRV or ERV works

An HRV pulls stale, moist air from rooms such as the kitchen, bathrooms and laundry and sends it outdoors, while bringing in the same amount of fresh outdoor air. The two airstreams pass each other in a heat-exchange core without mixing, and heat moves from the warm outgoing air to the cold incoming air. In summer the process reverses and some heat is kept out (NRCan HRV guide ↗).

NRCan's Keeping the Heat In ↗ says a typical HRV recovers 70 to 80% of the heat from the exhaust air; NRCan's ventilation fact sheet ↗ gives a range of 60 to 90% across models. An energy recovery ventilator (ERV) is a type of HRV that exchanges moisture as well as heat.

Fresh air reaches rooms through the furnace ducts or through dedicated ducts. With furnace ducts, the furnace fan has to run for the air to circulate, and Health Canada ↗ notes that an older furnace fan can draw 500 to 800 watts, compared with the 30 W fan motor in the most efficient HRVs. NRCan says a brushless DC (ECM) furnace motor can cut average furnace electricity use by more than 70% in continuous circulation, and that an HRV with its own ducts can be the most efficient setup, especially in a house without ductwork.

Ratings, sizing, and HRV versus ERV

Two ratings, both measured to the CSA C439 test standard, tell you how good a unit is:

• Sensible recovery efficiency (SRE): the share of heat recovered after accounting for fan energy, air leakage, frost control and other losses. ENERGY STAR certification in Canada (Version 2.3 ↗, effective December 13, 2021) requires at least 65% SRE at 0°C and 60% at −25°C.
• Fan efficacy: airflow per watt of fan power. ENERGY STAR requires at least 1.2 cfm per watt (0.57 L/s per watt) for units under 75% SRE, and 0.8 cfm per watt (0.38 L/s per watt) at 75% SRE or higher.

NRCan suggests choosing an ENERGY STAR model or one with Home Ventilating Institute (HVI) certification, with a high SRE and a low-energy fan motor. For an ERV, make sure it was tested at low temperature; all ENERGY STAR models are. Rated units are listed in NRCan's searchable product list ↗ and the HVI directory.

For sizing, NRCan's HRV guide allows 10 L/s (20 cfm) for the master bedroom, 10 L/s for an unfinished basement and 5 L/s (10 cfm) for each other room. A ten-room home works out to 60 L/s (120 cfm) at high speed, and low speed should be 40 to 60% of that.

HRV or ERV? NRCan recommends an ERV where cooling loads are high, where indoor moisture levels are very low, or in very dry climates such as northern Canada. Health Canada adds that an ERV can be the better choice for a house that is already dry in winter, and is preferable to an HRV for avoiding excess indoor humidity in summer. An HRV sends more of the winter moisture outdoors, which helps where windows sweat. If an HRV leaves the house too dry, NRCan says over-ventilation may be the cause; try a lower speed before changing equipment. Some HRVs can be converted to ERVs for less than a new unit.

Balancing and signs of trouble

An HRV is meant to move the same amount of air in as out. NRCan's guide explains that an unbalanced system recovers less heat and causes problems either way. More air out than in depressurizes the house, which can pull carbon monoxide and other combustion gases from a furnace, water heater or fireplace back indoors. More air in than out pushes moist indoor air into walls and the roof, where it can condense, and can frost the core.

The National Building Code 2025 ↗ requires installers to follow the manufacturer's start-up procedures, including air balancing and airflow measurement. NRCan recommends a balance check by a qualified contractor once a year, and a service with a balance test when you buy a home that already has an HRV.

For a rough check, CMHC ↗ suggests taping a large garbage bag to a coat hanger, holding it flat over the outdoor exhaust hood and timing how long it takes to inflate, then holding the inflated bag over the supply hood and timing how long it takes to deflate. The times should be roughly equal; if the bag inflates twice as fast as it deflates, the unit is unbalanced.

Warning signs from NRCan's troubleshooting guide:

• Little or no airflow at the grilles: blocked hoods, dirty filters, a frozen core or loose ducts.
• A core that keeps freezing. Most HRVs defrost automatically when incoming air is colder than −5°C, so repeated freezing points to dirty filters, a defrost fault or imbalance.
• Cold drafts near supply grilles, wet duct insulation or water on the floor.
• Stale air or condensing windows, or the reverse, air that is too dry in winter.

When you need one, and what an energy advisor checks

NRCan's rule: if a house already shows excessive condensation and the moisture sources can't be reduced, any retrofit that makes it more airtight has to include mechanical ventilation. It calls an energy-efficient HRV or ERV one of the best ways to ventilate a home. Health Canada notes that some jurisdictions require HRVs in new construction, while balanced and exhaust-only systems may be allowed in retrofits.

• Airtightness: a blower door test measures it, and Health Canada says the result helps determine which ventilation system best fits the house.
• Actual airflow: a ventilation assessment checks whether fans and any existing HRV move air outdoors as they should.
• Pressure safety: a combustion safety test confirms an unbalanced system or exhaust fan isn't depressurizing the house around fuel-burning appliances.

For installation, NRCan recommends a contractor trained through HRAI (the Heating, Refrigeration and Air Conditioning Institute of Canada) or, in Quebec, the CMMTQ. HRAI certifies HRV and ERV installation and balancing (VIBF).

Maintenance and upgrades, from simplest to biggest

In NRCan's maintenance chart, everything except the annual service is homeowner work. Disconnect the power first.

Mistakes to avoid

• Turning it off. NRCan's ENERGY STAR guidance ↗ says never to turn an HRV or ERV off except for servicing. Low speed year-round usually meets ventilation needs; use high speed for cooking, showers or a full house.
• Counting on it for combustion air. NRCan cautions not to rely on an HRV to remove combustion by-products or to supply combustion air for fuel-burning appliances.
• Using the wrong filters. Filters not designed for your unit can restrict airflow and impair operation.
• Expecting an air cleaner. NRCan says an HRV is not an air cleaner and may not handle strong pollutant sources such as smelly glues.
• Covering the hoods with fine mesh. NRCan says screen mesh finer than about 6 mm (¼ in.) blocks airflow. Keep garbage, pesticides and the barbecue away from the intake.
• Skipping commissioning. NRCan notes that historically many HRVs and ERVs were not installed or maintained properly, and says they must be installed, balanced and commissioned by a certified technician.

Rebates and next steps

Rebates vary by province and change often. Check current offers in our rebate program tracker, estimate the payback with the upgrade payback calculator, and use the home energy planner to sequence ventilation with air sealing. To find someone to measure your current airflow, see our ventilation assessment providers.