Heat Recovery Ventilation (HRV) System: How It Works and How to Choose
What Is a Heat Recovery Ventilation (HRV) System?
A heat recovery ventilation system — usually called an HRV, and in its total-heat variant an ERV (Energy Recovery Ventilator) — is a balanced mechanical ventilation unit that exhausts stale indoor air while supplying an equal volume of fresh outdoor air, and transfers the thermal energy between the two airstreams through an air-to-air heat exchanger core. The two streams never mix; only heat (and, in an ERV, moisture) crosses the separation wall. The result is continuous fresh air without throwing away the heating or cooling already paid for.
In cold climates a code-compliant HRV typically recovers 60–90% of the sensible heat that would otherwise be vented outdoors, which is why HRVs are now standard in passive houses, schools, offices, and anywhere tight building envelopes make uncontrolled infiltration both wasteful and unhealthy.
How an HRV Works
Two fans move air in opposite directions: an exhaust fan pulls indoor air out through the core, while a supply fan pulls outdoor air in through the same core on the other side. Because the airstreams are separated by thin plates (in a plate exchanger) or by the matrix of a rotating wheel, heat conducts from the warm exhaust to the cold supply in winter, and from the cool exhaust to the warm supply in summer for free cooling.
The key component is the recovery core. The three commercially dominant core types are:
- Plate (fixed-plate) exchangers — sensible-only recovery, no moving parts. See our plate heat exchanger overview.
- Rotary (enthalpy) wheels — rotating matrix that carries both heat and moisture. See rotary heat exchangers.
- Heat-pipe exchangers — passive, gravity-driven, good for certain industrial duties. See heat-pipe exchangers.
Sensible vs Total (Enthalpy) Recovery
A plain HRV recovers sensible heat only — it raises or lowers the supply air temperature but does not move moisture. An ERV (or an HRV fitted with an enthalpy wheel or membrane) recovers latent heat as well, transferring water vapor so indoor humidity stays balanced. The trade-off is detailed in our guide to sensible vs latent heat recovery, and the humidity question is answered directly in does a heat exchanger remove humidity.
Plate vs Rotary Wheel in an HRV
Most residential and light-commercial HRVs use a fixed plate core: it is silent, has no motor, and cannot leak supply and exhaust air into each other. A rotary wheel recovers more total energy (including moisture) and handles larger airflows, but it has a motor, needs seals, and — critically — carries a small cross-contamination risk because the same matrix touches both streams. Our rotary vs plate comparison and the field guide where rotary wheels shine and where they are banned explain when each is the right call. As a rule of thumb: in pharmaceutical exhaust, kitchens, and any duty where cross-contamination is unacceptable, a plate or heat-pipe core is preferred over a wheel.
Sizing and Airflow
HRV capacity is matched to the building's required ventilation rate (often derived from floor area or occupant count per local code) and expressed as supply/exhaust airflow in m³/h. Recovery effectiveness η is defined as:
η = (Tsupply − Toutdoor) / (Tindoor − Toutdoor)
For a design indoor 21°C, outdoor −10°C, and an 80% effective core, the supply air arrives at roughly −10 + 0.8×(21 − (−10)) = 15.8°C instead of −10°C — a massive pre-heat load removed from the heating system. Our sizing guide walks through the calculation step by step.
Recovery Efficiency You Can Expect
| Core type | Sensible recovery | Latent recovery | Moving parts |
|---|---|---|---|
| Cross-flow plate | 50–70% | None | No |
| Counter-flow plate | 80–90% | None | No |
| Rotary enthalpy wheel | 75–85% | 60–80% | Yes (motor) |
| Heat pipe | 55–75% | None | No (gravity) |
Selection Checklist
- Decide sensible-only (plate/heat-pipe) vs total (wheel/ERV) from your humidity climate.
- Confirm the duty allows a wheel — if not, specify plate or heat-pipe. See how to choose the right heat exchanger.
- Size to required airflow, not to peak; oversizing hurts effectiveness.
- Plan frost protection for cold-climate plates — see frost prevention.
Frequently Asked Questions
Do I need an HRV or just a fan?
A simple exhaust fan ventilates but vents energy. An HRV ventilates and saves the conditioning energy. In a tight, insulated building the HRV is almost always the better investment.
Can an HRV cool my home in summer?
A sensible HRV pre-cools incoming air using cool exhaust, reducing AC load. For strong summer free-cooling in data centers and equipment rooms, see our plate exchangers for data-center free cooling.
Talk to an Application Engineer
Our team designs air-to-air heat exchangers for HRV, ERV, and industrial energy-recovery duties in plate, rotary, and heat-pipe forms. For core selection, sample drawings, and a quotation, contact us at +86 15753355505.