Packaged rooftop HVAC units. In residential settings, heat recovery ventilators (HRVs) perform a similar air exchange function at smaller scale. Image: Wikimedia Commons / CC BY-SA.
Why Mechanical Ventilation Matters in Cold Climates
In older Canadian housing stock, natural infiltration through gaps around windows, doors, and wall penetrations provided incidental ventilation. A 1970s bungalow in Winnipeg often changed its air volume multiple times per hour through uncontrolled leakage. That same air change came at an enormous heating cost — outdoor air at −25°C has to be warmed to 20°C before it is comfortable.
Energy-efficient construction eliminates most of that leakage. A house built to NBC 2020 targets might achieve an airtightness of 1.5 air changes per hour at 50 pascals (ACH50) — significantly tighter than the 5–8 ACH50 typical of 1980s construction. This is beneficial for heating costs, but it means that moisture, CO2, volatile organic compounds (VOCs), and combustion by-products can accumulate without deliberate ventilation.
ASHRAE Standard 62.2-2019 sets a minimum whole-building ventilation rate of 0.35 air changes per hour, or 7.5 litres per second per person plus 0.15 L/s per square metre of floor area, whichever is larger. Many Canadian jurisdictions have adopted this standard by reference.
Heat Recovery Ventilators (HRVs)
An HRV addresses the core problem of cold-climate ventilation: how to exchange stale indoor air with fresh outdoor air without losing most of the heat in the process. The unit contains a heat-exchange core — typically a cross-flow or counter-flow plate exchanger made of thin polymer sheets or aluminium foil — through which outgoing warm air and incoming cold air pass in separate channels. Heat transfers from the exhaust stream to the supply stream without the two airflows mixing.
Sensible heat recovery efficiencies for residential HRVs in Canada commonly range from 70% to over 85% at 0°C, as measured under CSA C439 testing conditions. At lower temperatures, below roughly −15°C, most HRVs incorporate a defrost cycle where the intake is temporarily reduced or stopped to prevent frost formation on the core.
HRV vs. ERV
An energy recovery ventilator (ERV) works on the same principle but uses a hygroscopic core that transfers both sensible heat and moisture. In climates where winter air is very dry, an ERV helps retain indoor humidity rather than exhausting it — relevant for tightly-sealed Prairie homes where maintaining 30% relative humidity in February can already be challenging. On the other hand, ERVs are less appropriate in humid summer climates where you want to exhaust moisture rather than retain it.
Interior of a heat recovery ventilation unit showing the cross-flow heat exchange core. Image: Wikimedia Commons / CC BY-SA.
Installation Considerations
An HRV is typically installed in the mechanical room alongside the furnace, with supply and exhaust ducts distributed through the house. Common configurations tie HRV supply into the main forced-air duct system; alternatively, a dedicated balanced duct network runs separately from the heating system.
Duct balancing matters. An HRV that exhausts 80 CFM but only supplies 60 CFM creates a depressurization condition that can draw combustion gases from fuel-burning appliances — a recognized safety risk in Canada where gas furnaces, water heaters, and fireplaces are common. After installation, airflow balancing should be verified with a flow hood or anemometer.
Commissioning Checklist
- Verify supply and exhaust airflows are within 10% of each other at the unit's rated speed
- Confirm the defrost thermostat set point matches the manufacturer's specification for local climate
- Check that the heat exchange core is accessible for seasonal cleaning — dust and particulate accumulate on the exhaust side
- Ensure exhaust terminations are at least 2 metres from operable windows and HVAC intakes
- Confirm the outdoor air intake has a proper screen and is oriented to avoid prevailing-wind-driven rain or snowdrift accumulation
Building Code Requirements in Canada
The 2020 National Building Code (NBC) requires mechanical ventilation in all new residential construction. Individual provinces adopt and amend the NBC on their own schedules. Ontario's Building Code has required HRVs in new single-family homes since 2017. British Columbia's Energy Step Code and BC Building Code 2018 similarly mandate mechanical ventilation systems that meet ASHRAE 62.2 rates.
For existing homes undergoing renovation, requirements vary. Significant envelope improvements — such as adding exterior insulation or replacing windows throughout — may trigger ventilation upgrade requirements in some jurisdictions.
Operating an HRV Efficiently
Most residential HRVs have a simple two-speed or variable-speed control. Running the unit at low speed continuously is generally more energy-efficient than cycling it at high speed intermittently, because the heat exchange efficiency is higher at lower airflows.
A common practice in Canadian homes is to run the HRV at low continuous speed for baseline ventilation and to boost it during cooking, showering, or when occupancy is high. Some systems integrate with smart thermostats and CO2 sensors that adjust ventilation rate based on measured indoor air quality.
The HRV core should be cleaned once or twice per year. The exhaust-side filter traps lint and particulate; a clogged filter reduces airflow and lowers heat recovery efficiency. Many manufacturers recommend cleaning with warm water and mild soap, followed by air-drying before reinstallation.