In a house built to current Canadian energy standards, natural air changes through wall leakage are minimal by design. The air sealing that reduces heating and cooling losses also means that stale indoor air, moisture, and pollutants have no passive pathway out. Mechanical ventilation fills that gap — and in Canada, the two most common residential approaches are heat recovery ventilators (HRV) and energy recovery ventilators (ERV).
Both systems exchange stale indoor air with fresh outdoor air while recovering a significant portion of the thermal energy that would otherwise be lost. Where they differ is in how they handle moisture, and that distinction matters considerably in a country with the climate diversity of Canada.
How an HRV Works
An HRV contains a heat exchanger core — typically made of polymer or aluminum plates — through which two airstreams pass in close proximity but without mixing. The outgoing stale air transfers heat to the incoming fresh air. The effectiveness of this heat transfer, expressed as sensible heat recovery efficiency, typically ranges from 70 to 80 percent in units certified to the HVI (Home Ventilating Institute) standard, and can exceed 90 percent in premium units tested at low temperatures.
The incoming air is pre-warmed before it enters the living space, which reduces the energy penalty of ventilation compared to opening a window. The HRV does not transfer moisture — the two airstreams remain physically separated, so water vapour passes through in one direction only (out, with the exhaust stream).
Frost Control
In Canadian winters, incoming outdoor air at temperatures below approximately -20°C to -25°C can cause moisture from the exhaust stream to freeze on the core, reducing effectiveness and potentially damaging the unit. HRVs manage this through a defrost cycle: the unit temporarily reduces or reverses outdoor airflow, allowing the core to warm. The specific defrost approach varies by manufacturer. Units certified to CSA C439 — the Canadian standard for residential HRVs — must demonstrate adequate frost protection for Canadian conditions.
How an ERV Differs
An ERV uses a permeable or desiccant-based core that transfers both sensible heat (temperature) and latent heat (water vapour/humidity) between the two airstreams. In winter, this means that moisture from the outgoing humid indoor air is transferred to the drier incoming outdoor air, retaining humidity in the home. In summer, moisture from warm humid outdoor air is transferred to the drier indoor air, reducing the latent cooling load on the air conditioning system.
The key trade-off: an ERV is less effective at removing excess indoor humidity in winter. In climates where the primary moisture concern is dry indoor air — northern Prairie provinces and parts of northern Ontario in deep winter — an ERV can help maintain comfort without running a separate humidifier. In climates where indoor humidity management is more about removal than retention (coastal British Columbia, parts of Atlantic Canada), an HRV's ability to expel moisture with the exhaust air is typically more appropriate.
Comparison Summary
| Feature | HRV | ERV |
|---|---|---|
| Heat recovery | Yes (sensible) | Yes (sensible + latent) |
| Moisture transfer | No | Yes (partial) |
| Best climate fit | Humid to mixed; cold winters | Dry cold winters; hot humid summers |
| Frost protection | Defrost cycle required | Less frost-prone (core material absorbs moisture) |
| Core material | Aluminum, polypropylene | Desiccant paper, polymer membrane |
| Core maintenance | Washable every 3–6 months | Do not wash (degrades desiccant) |
Canadian Code Requirements
Section 9.32 of the National Building Code of Canada (NBC) addresses mechanical ventilation in Part 9 buildings — low-rise residential construction. It specifies minimum ventilation rates based on house volume and the number of bedrooms, and requires that ventilation systems in new construction be capable of providing these rates when the house is occupied.
ASHRAE Standard 62.2 — Ventilation and Acceptable Indoor Air Quality in Residential Buildings — is referenced by several Canadian provincial codes and provides a performance-based framework for calculating required ventilation rates based on conditioned floor area and number of bedrooms. The minimum airflow rates in these documents represent thresholds for acceptable dilution of occupant-generated contaminants; they do not account for source-specific issues like elevated radon or VOC concentrations.
Natural Resources Canada (NRCan) provides guidance on HRV/ERV selection as part of its EnerGuide program for homes and its R-2000 advanced housing standard, both of which include requirements for mechanical ventilation performance.
Sizing and Installation Considerations
Undersized units fail to deliver adequate fresh air. Oversized units may over-ventilate in mild weather, increasing energy consumption and potentially overcooling or overdrying the home. Sizing is based on the required ventilation rate (in litres per second or cubic feet per minute), which depends on the home's floor area and occupancy, as calculated per NBC 9.32 or ASHRAE 62.2.
Duct layout affects performance significantly. Long duct runs with multiple elbows increase static pressure and reduce effective airflow. HRV/ERV units are typically connected to the existing forced-air system ductwork or installed with dedicated ducting. The fresh air supply should ideally be distributed to bedrooms and main living areas; exhaust should be drawn from bathrooms and the kitchen. This creates a ventilation pattern that dilutes pollutants where they are most concentrated and delivers fresh air where occupants spend the most time.
Balanced Pressure
Both HRVs and ERVs are designed to operate with balanced airflows — the volume of air brought in should roughly equal the volume exhausted. An imbalanced system creates positive or negative pressure in the house, which drives air (and its pollutants, moisture, or radon load) through the building envelope at unintended locations. Commissioning — measuring and adjusting airflows after installation — is required under the NBC and is a step that is sometimes skipped in practice, with consequences for both performance and energy use.
Maintenance
HRV cores should be inspected and cleaned every three to six months during active use. Filters on both the intake and exhaust sides require regular replacement or cleaning depending on the unit design. A dirty or clogged filter increases static pressure and reduces airflow without any visible symptom from the occupant's perspective — the unit appears to operate normally but is delivering less fresh air than required.
ERV cores, because of their desiccant or membrane construction, cannot be washed. They should be inspected for debris but are typically replaced rather than cleaned when contaminated. The replacement interval varies by manufacturer and conditions; units in dusty environments or in homes with pets may require more frequent attention.
HVI publishes a directory of certified residential ventilation products, including HRVs and ERVs tested to applicable performance standards. CSA C439 is the Canadian standard for performance testing of residential ventilating systems. Both are referenced by Canadian building codes and procurement specifications.