How an energy recovery ventilator works

An energy recovery ventilator (ERV) brings in fresh outdoor air and exhausts the same amount of stale indoor air, passing both streams through a core of thin plates. Heat moves through the plates from the warmer stream to the cooler one, and an ERV core also moves some moisture. In winter, fresh air is prewarmed by the outgoing air, so ventilation costs far less energy.

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Outdoor temperature

Indoor air is held at 21 °C.

Core effectiveness

Airflow each way

Step through it

Two airstreamsOne fan pulls fresh outdoor air in while another pushes stale indoor air out, in equal amounts, so the house stays at neutral pressure.
The coreInside the core the streams flow through alternating channels separated by thin plates. They never mix, but heat passes through the plates.
Winter prewarmingOn a cold day the outgoing warm air heats the incoming cold air. At minus 20 °C outdoors, a 70 percent core delivers air near 8.7 °C.
Summer precoolingWhen it is hot outside the process reverses: cool indoor air precools the fresh air, and an ERV core also sheds some of the incoming humidity.
Better coresA higher effectiveness core recovers more of the temperature difference, leaving less work for the furnace or air conditioner.

Effectiveness

Sensible effectiveness is the fraction of the indoor to outdoor temperature difference that the core recovers. Supply temperature = T outdoor + effectiveness x (T indoor minus T outdoor). With 0 °C outside, 21 °C inside and 70 percent effectiveness, fresh air arrives at about 14.7 °C.

Recovered power is air mass flow times specific heat times the temperature rise of the fresh air, using 1.2 kg/m³ and 1.006 kJ/kg·K. This model treats sensible heat only and ignores the moisture an ERV core also exchanges, so it understates savings in humid weather.

Try it: set the outdoor temperature to minus 20 °C and airflow to 150 L/s. Energy recovered climbs past 5 kW, heat that a plain exhaust fan would simply throw away.

Why tight houses need them

Modern homes are sealed so well that they need mechanical ventilation for healthy indoor air. Balanced ventilation with energy recovery provides that fresh air while keeping most of the heating and cooling energy indoors.

Sources

HVAC Energy Recovery VentilationU.S. DOE Building Science Education
Residential Heat Recovery Ventilation Technical Brief (PNNL-28354)U.S. DOE Office of Scientific and Technical Information
A Review of Heat Recovery Technology for Passive Ventilation ApplicationsUniversity of Sheffield (White Rose Research Online)

How to cite this model

Avid Solutions International. (2026, November 11). How an energy recovery ventilator works [Interactive 3D model]. Avid Field Lab. https://avidsolutionsintl.com/explore/energy-recovery-ventilator

Last updated November 11, 2026

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