Air
Energy Recovery Ventilator
ERV
Also known as energy recovery ventilation, enthalpy ventilator
A balanced ventilation system that exhausts stale indoor air and supplies outdoor air through a core that transfers both heat and a portion of moisture between the two air streams.
In more detail
An ERV runs two ducted air streams past each other through an exchange core. Outgoing air gives up heat to incoming air in winter and absorbs heat from it in summer, so the house gets outdoor air without paying full price to condition it. The distinguishing feature is the enthalpy core, which also transfers water vapor — some of the humidity in the outgoing stream is passed back in winter, and some of the humidity in incoming summer air is shed before it reaches the house.
Balanced is the operative word. An ERV supplies and exhausts roughly equal volumes, so it ventilates without pressurizing or depressurizing the building. That distinguishes it from exhaust-only ventilation, which pulls replacement air through whatever gaps the enclosure happens to have.
An ERV is a ventilation device, not an air cleaner and not a dehumidifier. It dilutes indoor pollutants with outdoor air and moderates the energy and moisture cost of doing so. Filtration of the incoming stream is a separate function, typically a filter rack ahead of the core, and humidity control beyond partial transfer requires dedicated equipment.
Why it matters
As homes get tighter, accidental leakage can no longer be relied on to provide adequate ventilation, so something has to bring outdoor air in deliberately. ERVs are often selected where moisture transfer is useful, but the choice between an ERV and an HRV depends on climate, occupancy, internal moisture generation, enclosure performance, ventilation rate and the interior humidity the household wants. Either unit runs continuously and quietly at low volume, which is why it tends to be forgotten until the filters are two years overdue.
The common misunderstanding
That an ERV cleans the air, or that it controls humidity. Neither is what it does. It exchanges air and recovers some of the energy and moisture in the process. Particle and gas removal come from filtration, and real humidity control comes from a dehumidifier or the cooling system. The related confusion is treating ERV and HRV as interchangeable. They differ specifically in moisture transfer, and which one suits a house depends on climate and on the interior humidity the occupants want.
Related terms
On Compound
Where this term does real work — and where the decisions get made.
Sources
Last reviewed July 2026 by Compound Editorial. Definitions are educational and not project-specific engineering or medical advice.