Heat recovery ventilation
Heat recovery ventilation uses a heat exchanger to transfer heat between outgoing stale indoor air and incoming outdoor air. HRV and ERV systems provide controlled fresh air while reducing the heating or cooling energy lost through ventilation, especially in airtight buildings.
What heat recovery ventilation is
Heat recovery ventilation is a mechanical ventilation strategy that brings outdoor air in and sends stale indoor air out through a heat exchanger. The two air streams usually pass near each other without mixing. In winter, outgoing warm air preheats incoming cold air. In summer, outgoing cooler air can pre-cool incoming hot air. The goal is fresh air with less energy waste than simply exhausting conditioned air and pulling outdoor air through leaks.
How an HRV works
A heat recovery ventilator, or HRV, uses fans and a core that transfers sensible heat between exhaust and supply air. Sensible heat is the heat connected to temperature. A balanced HRV normally moves similar amounts of air in and out, reducing pressure problems compared with exhaust-only or supply-only ventilation. Filters, ducts, balancing dampers, controls, and condensate management are part of the working system.
How an ERV differs
An energy recovery ventilator, or ERV, transfers sensible heat and some latent energy associated with water vapor. This can help moderate humidity in some climates by transferring part of the moisture load between air streams. ERVs do not replace dehumidifiers, humidifiers, or good moisture control, but they can reduce the penalty of ventilating when outdoor and indoor humidity conditions are very different.
Why airtight buildings need planned ventilation
Air sealing reduces uncontrolled leaks, but people still need outdoor air and pollutant removal. Heat recovery ventilation pairs well with airtight construction because it separates two goals: the envelope limits random air leakage, while the ventilation system provides intentional air exchange. That distinction supports comfort, indoor air quality, energy efficiency, and moisture control.
Efficiency and effectiveness
HRV and ERV performance depends on heat-exchanger design, airflow rate, fan power, duct leakage, defrost operation, filter condition, climate, and installation quality. A high-rated unit can underperform if ducts are leaky, unbalanced, too restrictive, or routed through extreme temperatures. Useful design looks at the whole system, not just the recovery efficiency printed on a product sheet.
Cold, humid, and mixed climates
Cold climates may need frost protection because moisture in outgoing air can freeze in the core. Hot-humid climates need careful humidity strategy so ventilation does not overload cooling and dehumidification. Mixed climates can make HRV-versus-ERV choices less obvious. The best system depends on climate, indoor humidity goals, occupancy, airtightness, HVAC design, and maintenance expectations.
Distribution and controls
Some systems deliver fresh air to bedrooms and living spaces while exhausting bathrooms, kitchens, laundry rooms, or central return areas. Others use simplified duct layouts or connect to existing HVAC ducts. Controls may run continuously, intermittently, by schedule, by occupancy, or in response to humidity or carbon dioxide. Good commissioning verifies actual airflow, balance, noise, and control settings.
Maintenance and limits
Heat recovery ventilation needs maintenance. Filters clog, exterior hoods can block, drains can fail, fans can drift, and occupants may turn systems off if they are noisy or confusing. HRVs and ERVs also do not solve every indoor air problem: source control, filtration, moisture management, combustion safety, radon mitigation, and adequate exhaust at pollutant sources still matter.
Why it matters
Heat recovery ventilation matters because better envelopes make random leakage less acceptable as a ventilation strategy. HRVs and ERVs let buildings be both tighter and fresher when they are designed, installed, balanced, and maintained well. They help connect energy efficiency with health and comfort instead of treating ventilation as a simple energy loss.