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Musings of an Energy Nerd

Misconceptions About HRVs and ERVs

A heat-recovery ventilator isn’t a space heating appliance, makeup air unit, dehumidifier, or energy-saving device

A heat-recovery ventilator (HRV) supplies fresh outdoor air to a house while simultaneously exhausting an equal volume of stale air. Because the supply air stream and the exhaust air stream pass through adjacent air channels in the heat-recovery core, some of the heat from the warmer air stream is transferred to the cooler air stream. The two air streams don't mix. [Click on the image to enlarge it.]
Image Credit: PNNL

Since refrigerators have been around for almost a hundred years, most Americans know what a refrigerator is used for. But heat-recovery ventilators (HRVs) and energy-recovery ventilators (ERVs) have only been around for about 30 years, and many Americans still don’t know much about these appliances.

GBA regularly receives questions that show that some homeowners are confused about the purpose of these appliances, so it’s worth examining and debunking common misconceptions about HRVs and ERVs.

Not a space heating appliance

Journalists who try to describe HVAC equipment in a Passivhaus building are sometimes confused about the distinction between ventilating equipment and space-heating equipment. That’s why they write sentences like these: “This home doesn’t have a furnace or a boiler. A heat-recovery ventilator supplies all of the heat needed to keep the house warm.”

In fact, HRVs and ERVs are ventilating appliances designed to introduce fresh air into a house and to exhaust stale air from the house. (While an HRV has a core that transfers heat from one air stream to the other, an ERV has a core that transfers both heat and moisture. For more information on HRVs and ERVs, see the GBA article titled HRV or ERV?)

These ventilating appliances aren’t designed to provide heat. On the contrary: during the winter, operating an HRV or ERV will tend to lower, not raise, the indoor air temperature. While it’s true that these appliances have a heat-exchange core, the efficiency of these heat exchangers is necessarily less than 100% — so operating an HRV or ERV during the winter inevitably sends some of the home’s heat outdoors.

The confusion arises because some Passivhaus builders install a heater — for example, an electric resistance heating coil or the…

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