There are two main types of air exchangers: heat recovery and energy recovery.

The Heat Recovery Air Exchanger (HRV) has a heat recovery core that transfers much of the heat from the stale and exhaust air to the fresh air you draw outside of the House. Therefore, stale air and fresh air do not mix.

As for the energy recovery air exchanger (ERV), in addition to recovering heat like the HRV, it also recovers the energy contained in the ambient humidity. If needed, it limits the amount of moisture entering the home and thus helps maintain a constant humidity level in the home throughout the year. It also saves on heating and cooling costs while improving the efficiency of these systems, hence the name “energy recovery.”

Common functions of HRV and ERV

The two types of systems have the following functions in common:

• Ventilation: HRV and ERV expel indoor air pollutants (odors, fumes, dust, gas, etc.), as well as excess humidity.

• Supply of new air: they guarantee the complete renewal of the air in the house every three hours: at the end of this interval, an equivalent volume of new air, coming from the outside, replaces that evacuated.

• Filtration: both fans are fitted with a filter that limits the entry of pollen, dust, and insects that can enter with fresh air.

• Distribution: they are connected to a network of air ducts that extends to all the rooms, except the garage. This network can sometimes be combined with the pipes of a centralized heating system.

• Heat recovery: The most common versions of both devices today have a core in which the incoming and outgoing air crosses without touching each other due to the thin walls. These aluminum or polypropylene walls are airtight but conduct heat. This property allows them to transfer, in winter, part of the heat from the outgoing air to the incoming air; the recovered heat represents energy savings.

The major difference between the two systems

The big difference between HRV and ERV is in their cores. While the walls of the HRV recovery core are moisture-proof, those of the ERV is different: they contain a desiccant material (which absorbs some of the moisture).

ERV redirects moisture from the more humid air stream to the drier air stream. In winter, humidity is usually higher indoors than outdoors, so ERV dries out the outgoing air and humidifies the incoming air. In other words, during the cold season, ERV keeps more moisture in the house than HRV.

Summer and air conditioning

In summer, unlike HRV, ERV can “help” the air conditioner in its dehumidification efforts by transferring some of the moisture from the incoming air to the outgoing air. This factor must be taken into account in warmer regions of the world, but in Quebec, the choice of an HRV or an ERV must be made according to winter conditions.

Which one to choose?

Therefore, the choice of an HRV or an ERV depends on the humidity level in a building, but also on the following factors:

• Number of people in the house: An HRV can meet the needs of a large family that generates a lot of humidity. On the other hand, the fewer people there are in a house, the drier the air becomes and the more appropriate the VRE is.

• Dimensions: In principle, an HRV is suitable for small to medium-sized homes, where moisture can build up quickly. An ERV, on the other hand, will be more useful in larger homes where the air tends to be drier.

• Building waterproofing: the more waterproof your home, the more moisture can be trapped there and the more relevant the HRV will be.

• Type of Heating – In a wood-fired home, which is generally drier, VRE will help restore healthy humidity to the interior.

• Regional climate: this is another determining factor. The VRÉ is suitable for cold and dry climates in Quebec and the Hautes-Laurentides, for example. The HRV works best during milder, wetter winters like Montreal and the Eastern Townships.

Performance and installation

Ready to choose between ERV and HRV? In any case, you should consider a device whose performance has been certified by the Home Ventilating Institute (HVI) and meets the energy efficiency criteria of the Energy Star program. To be eligible, HRVs and ERVs must have a sensible heat recovery efficiency (HRE) of at least 65% at 0 degrees Celsius and at least 60% at -25 degrees Celsius.

Finally, don’t leave the installation of your future system to the first person: HRVs and ERVs require a perfect balance between incoming and outgoing airflows. In short, only a contractor specializing in residential ventilation should see it… After all, it is the air that you and your loved ones breathe on a daily basis!