Both heat recovery ventilators (HRVs) and energy recovery ventilators (ERVs) bring in fresh outdoor air and exhaust stale indoor air while recovering heat from the outgoing stream. The difference is moisture: an HRV transfers heat only, while an ERV also transfers some humidity. Which one fits depends on whether your building tends to be too humid or too dry, and on how cold your winters are.
How recovery ventilators work
A recovery ventilator has two fans and a core. One fan pulls stale air from kitchens, bathrooms or general spaces and sends it outside. The other draws in outdoor air and supplies it to the building. The two airstreams pass through the core without mixing, and heat moves from the warmer stream to the cooler one. In winter, outgoing warm air preheats incoming cold air. In summer, the process can work in reverse to precool incoming air.
The result is balanced ventilation with much less energy spent heating or cooling the outdoor air than if it came in directly.
HRV and ERV compared
| HRV | ERV | |
|---|---|---|
| Transfers heat | Yes | Yes |
| Transfers moisture | No (condensate drains away) | Yes, partly |
| Effect in winter | Removes indoor moisture with exhaust air, which tends to dry the building | Returns some moisture indoors, helping to limit dryness |
| Effect in humid summers | Brings outdoor humidity in | Reduces the humidity brought in with outdoor air |
| Condensate drain | Usually needed | Often not needed, depending on the unit |
| Typical fit | Buildings with too much indoor moisture in winter | Buildings that become very dry in winter, or face humid summers |
Choosing for Canadian conditions
When an HRV makes sense
If a building tends to have too much moisture in winter, an HRV helps by exhausting humid indoor air. That includes tightly built houses with many occupants, buildings with condensation on windows, and spaces with high moisture loads such as some residential suites. HRVs have long been common in much of Canada for this reason.
When an ERV makes sense
In very cold, dry climates, an HRV can over-dry a building in winter, leading to discomfort, static and the need for added humidification. An ERV keeps some moisture indoors. ERVs also help where summers are humid, such as much of southern Ontario, by reducing the moisture load on the cooling system. In larger commercial buildings with high ventilation rates, the moisture transfer can make a noticeable difference to humidifier and cooling energy.
It depends on the building, not just the climate
Two buildings in the same city can need different solutions. Consider occupancy, internal moisture sources, envelope tightness, existing humidification and dehumidification, and how much outdoor air the codes require. A designer can model these, and an inspection of how the existing building behaves through the seasons is valuable input.
Frost and cold weather
In cold weather, moisture in the exhaust air can freeze in the core and block airflow. Units handle this with defrost strategies such as recirculating indoor air, preheating outdoor air or temporarily reducing supply airflow. Defrost reduces ventilation while it runs, so in the coldest parts of the country it is worth confirming that the unit and its defrost approach suit the local winter design temperatures. Ask the manufacturer or designer, and check that defrost controls work during your first cold spell.
Balance matters. A recovery ventilator should supply and exhaust roughly equal amounts of air. An unbalanced unit can pressurize or depressurize the building, pushing moist air into walls or drawing combustion gases back from appliances. Have airflows measured and balanced after installation.
Maintenance
- Clean or replace filters on the schedule the manufacturer recommends.
- Clean the core as recommended. Some ERV cores cannot be washed with water, so follow the instructions.
- Keep outdoor intake and exhaust hoods clear of snow, leaves and nests.
- Check the condensate drain and trap on HRVs.
- Confirm both fans run and controls switch speeds as intended.
- Recheck airflow balance after any changes to ductwork.
A recovery ventilator that is not maintained can lose much of its airflow without anyone noticing. Our guide on ventilation and indoor air quality explains why that matters.
How ehZee can help
As part of our mechanical system inspections, we check recovery ventilators for condition, maintenance and whether they are delivering the ventilation they should. If you are deciding between an HRV and an ERV for a replacement or retrofit, we can review how your building behaves and help you frame the question for your designer.
Common questions
Is an ERV a dehumidifier?
No. An ERV reduces the moisture brought in with outdoor air in humid weather, but it does not remove moisture generated indoors the way a dehumidifier or air conditioner does.
Can I replace an HRV with an ERV?
Often, yes, but check that the unit suits your climate's winter temperatures, that ducting and controls are compatible, and that the change suits the building's moisture conditions.
Do recovery ventilators save energy?
They reduce the energy needed to condition outdoor air compared with bringing it in directly. They do use fan energy, so the benefit depends on the climate, the unit's efficiency and how many hours it runs.