Unless you already have this kind of unit in your home, chances are you wouldn’t know what the letters HRV (heat recovery ventilator) and ERV (energy recovery ventilator) refer to; both are centralized mechanical systems designed for existing homes. First, a little bit of history, then a look into their function, major difference and some help choosing the right one.
Ventilation yesterday and today
In the past, home ventilation was at the mercy of air leaking in and out. The result: poor comfort, heat loss and little control over air quality.
The advent of range hoods and bathroom fans improved things by removing smoke, odours and excess humidity. As houses became more and more airtight, though, air recirculation became an important issue. Early air exchangers were an answer to the problem; HRV and ERV units are newer and better versions of these devices.
What HRVs and ERVs do
The two types of system have the following functions in common:
Evacuation – HRVs and ERVs expel pollutants suspended in the house’s interior air (e.g., odours, smoke, dusts, gases) along with excess humidity.
Fresh air – They recirculate the air inside the home every three hours: once the cycle is complete, an equivalent volume of fresh air will have replaced what has been expelled.
Filtration – Both ventilators are equipped with a filter that limits ingress of pollen, dust and insects that may get in with fresh air.
Distribution – HRVs and ERVs are linked via ductwork to every room in the home, except the garage. In certain cases, they may be linked to an existing central heating system.
Heat recovery – Today’s most popular versions of both types of unit have a core in which the incoming and outgoing air crosses paths without actually touching, due to thin dividing walls. These dividers, made of aluminum or polypropylene, are airtight but can transfer sensible heat. As a result, in winter some of the heat leaving the unit is transferred to the incoming air. This heat recovery translates to energy savings.
The major difference between HRV and ERV units is in their cores. While an HRV’s heat recovery core’s dividing walls are sealed against humidity, those in an ERV are different: they contain a desiccant material (which absorbs some of the humidity).
The ERV redirects humidity from the more humid airflow to the least humid flow. In winter, when humidity levels are generally higher inside than outside, the ERV dries outgoing air and humidifies incoming air. In other words, during the cold season, an ERV keeps more humidity in the house than an HRV.
What about summer and air conditioning?
In summer, unlike HRVs, an ERV can “help” a home air conditioner’s dehumidification process by transferring some of the humidity from incoming air to outgoing air. This is important in warmer climes, but in Quebec, the choice between HRV and ERV units should be based on winter conditions!
Making your choice
The choice between HRV and ERV units depends, in large part, on the humidity levels in the building—but the following points should also be considered:
- Number of people in the home – An HRV fits the needs of a larger, active family that generates a lot of humidity. Conversely, the fewer people in the home, the drier the air will be, in which case the ERV is the better choice.
- Dimensions – In general, HRV units are best suited to small or medium-sized homes, where humidity can quickly accumulate. ERVs, on the other hand, will better serve larger homes where the air tends to be drier.
- Airtightness of the building – The better the envelope is sealed, the more humidity stays in, making the HRV the way to go.
- Type of heating system – In a wood-heated environment, which is more likely to be drier, an ERV will promote a healthier humidity level.
- Regional climate – Another determining factor. ERVs are best suited for colder, drier climates like those of Quebec City and the Upper Laurentians, for example. HRVs work better in the milder, more humid winters of Montreal and the Eastern Townships.
Performance and installation
Ready to choose between HRV and ERV? Whichever type you select, look for a model whose performance has been certified by the Home Ventilating Institute (HVI) and meets the energy efficiency requirements of the Energy Star program. To qualify, HRV and ERV units must show a sensible heat-recovery efficiency (SRE) rate of at least 65% at 0 degrees Celsius and at least 60% at -25 degrees Celsius.
Finally, do not entrust the installation of your new system to the first bidder: both HRV and ERV systems need to be perfectly calibrated to balance incoming and outgoing airflow. In short, only a qualified residential ventilation specialist should be hired… After all, it’s all about the air you and your family are breathing every day!