In a Canadian house that is built tight, the ventilation system is not an accessory. It is the only thing standing between a well-sealed envelope and a winter of condensation on the windows. The ERV-versus-HRV question is the first decision in that system, and it is usually argued badly — as a matter of preference rather than of moisture balance.
Both devices are air-to-air recovery ventilators. The difference is what they recover.
The definition that matters
Natural Resources Canada’s energy efficiency regulations define the two categories precisely, and the definitions are worth reading because they remove the marketing language:
- A heat-recovery ventilator (HRV) transfers heat between two isolated airstreams.
- An energy-recovery ventilator (ERV) transfers heat and moisture between two isolated airstreams.
Both are defined in the regulations for units with a maximum rated airflow of not more than 142 L/s (300 CFM) at 0°C. Both are tested to CAN/CSA-C439-18, Laboratory methods of test for rating the performance of heat/energy-recovery ventilators. Both have been subject to a federal performance reporting requirement for units manufactured on or after 1 January 2020 — and that reporting includes the sensible heat recovery efficiency at 0°C, and at −25°C unless the unit is marked for use only where the outdoor design temperature is at or above −10°C.
That last clause is the one to keep in mind when someone offers a ventilator described as “good for cold climates” without documentation. In Canada, −25°C performance is part of the conversation.
What each one does to your house in winter
An HRV brings in cold outdoor air, warms it against the outgoing stale air, and delivers it to the house. In doing so it brings in whatever absolute humidity the outdoor air carries. In a Canadian January, that is very little.
An ERV does the same, and also transfers some moisture between the airstreams. The direction of that transfer follows the humidity gradient, and that is the part people get wrong.
| Situation | HRV | ERV |
|---|---|---|
| Winter: house too dry, windows fine | Dries further | Tends to hold more moisture indoors |
| Winter: house too dry, heavy window condensation | Dries further, which may help the windows | May hold moisture that shows up on cold glass |
| Winter: normal occupants, tight new build | Common choice; simple, fewer parts | Common choice where dryness is the complaint |
| Summer: outdoor air is humid | Brings in moisture | Can temper incoming moisture |
| Core maintenance | Core is washable in soapy water | Core is washable in soapy water; check the manufacturer’s method |
| Frost handling | Requires a defrost strategy | Requires a defrost strategy |
| Failure modes | Fewer — no moisture transfer medium | Moisture transfer medium must stay clean and undamaged |
The rule we give distributors is blunt: the house decides, not the brochure. If the occupants complain about dry skin, static and wood movement all winter, an ERV is worth considering. If the complaint is condensation and ice on the inside of triple-glazed windows, adding moisture recovery may make it worse, and an HRV is the safer specification.
Do not decide from a rule of thumb about house age. Decide from the measured indoor relative humidity in winter, the number of occupants, and the moisture sources — cooking, showers, laundry, and any humidifier already in the house.
The numbers you should be reading
Every ventilator rating should come with test conditions attached. Our AspireVent range, for example, is published as 136 CFM at 0.4 in. w.g with a sensible recovery efficiency of up to 77%, and 152 CFM at 0.4 in. w.g with up to 77.4%. Note what those statements contain: an airflow, a static pressure, and a recovery efficiency — three numbers, not one.
- Airflow at a stated static pressure. Airflow without static pressure is marketing. Ductwork and terminations consume pressure, and the delivered airflow is what matters.
- Sensible recovery efficiency (SRE). How much of the sensible heat in the exhaust stream is transferred to the supply stream. This is the number with a regulatory definition behind it.
- Total recovery (for ERVs). Some manufacturers publish total recovery, which includes latent transfer. It is a bigger number than SRE, and it is not the same number. Compare like with like.
- Net supply airflow. Some ratings subtract the imbalance and internal leakage. Ask whether the figure is gross or net.
- Sound. Look for a rating, and note the test condition.
If a supplier cannot tell you the airflow, the static pressure, and the recovery efficiency for a specific model, the specification is not finished.
Frost, and the Canadian failure modes
Every ventilator in a Canadian winter will see frost. The heat exchange core is where exhaust air meets incoming cold air, and the exhaust side is carrying moisture. The unit must have a strategy: a periodic core defrost cycle, a recirculation damper, or a preheater. Whatever the strategy, it has a cost — reduced net ventilation during the cycle, or added electrical load.
Three failure modes we see in the field:
- Frost blockage on a unit with no functioning defrost. Delivered airflow collapses in January, and nobody notices until the windows sweat.
- Unbalanced airflow. A ventilation system that exhausts more than it supplies depressurizes the house and pulls make-up air through unintended paths. Look for auto-balancing without flow keys, and verify the balance at commissioning.
- Dirty or damaged core. A washable core stays effective if it is actually washed — in soapy water, per the manufacturer’s instruction — and reinstalled the right way round. A moisture-transfer medium that is clogged or torn stops doing its job.
Choosing, in eight steps
- Confirm the ventilation rate the house requires. In Canada, residential ventilation is commonly specified against ASHRAE Standard 62.2, and local codes may be stricter.
- Measure indoor relative humidity in winter, and note any window condensation.
- Count moisture sources: occupants, showers, cooking, laundry, and any existing humidifier or dehumidifier.
- Decide whether the house needs moisture added or removed in winter. That decision selects ERV or HRV.
- Confirm cold-weather performance and the defrost strategy in writing.
- Compare airflow at the static pressure your duct design will actually produce, not at zero.
- Confirm the core service method, the filter arrangement, and whether a controller and timer are included or optional.
- Confirm documentation: the test standard behind the rating, and the certification mark on the nameplate — in Canada, the “c” prefix version or a combined mark. Check the NRCan registration status before import.
What to put in the submittal
The ventilator page in a submittal should carry: the model, the port arrangement and orientation, airflow and recovery efficiency with test conditions, the balancing method, the defrost strategy, the controller and whether it interlocks with the furnace, and the maintenance instructions for the core.
Our ERV/HRV family page lists what we build — 100 and 150 CFM, side or top port, ECM 3-speed motors in a sealed housing with automatic reset thermal protection, auto-balancing without flow keys, and a heat recovery core that is washable in soapy water — along with the warranty terms. Our smart thermostat can control ventilation natively, including an outdoor-temperature lockout, which is the piece that stops a ventilator from running when it should not.
For how the ventilator sits alongside dehumidification, filtration and ducting, see the ventilation solutions hub and the indoor air quality hub. If the moisture problem in the house is a summer problem rather than a winter one, the answer is usually not an ERV — it is dehumidification, which we cover on the whole-house dehumidifier page.