Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards
An HRV and an ERV both bring in outdoor air and exhaust stale indoor air through a heat exchanger. The difference is moisture: according to the Department of Energy’s Building America guidance, “HRVs transfer sensible heat only; they do not transfer moisture”, while ERVs “transfer both heat and moisture.”
Whether a house needs either is increasingly a code question. Building America notes that residential code requires air leakage of 5 air changes per hour at 50 pascals or less and “specifically requires mechanical ventilation” in homes that tight.
Why tight houses need mechanical ventilation
Older houses ventilated themselves through leaks, badly and unevenly. As construction and retrofits seal those leaks for energy reasons, the air exchange that used to happen by accident has to be provided on purpose. Indoor CO2 is a common gauge of whether enough arrives, and our guide to indoor CO2 levels explains what the readings mean.
Building America summarises the code position: for dwellings with an air infiltration rate below 5 air changes per hour when tested with a blower door, mechanical ventilation is required. The flow rates are set by ASHRAE Standard 62.2, a private standard the codes reference.
The three ways to ventilate
| Strategy | How it works | Trade-off |
|---|---|---|
| Exhaust-only | Kitchen, bath or laundry fans exhaust air; replacement air “is pulled in through leaks in the building envelope or through passive vents” | Cheapest; replacement air comes from wherever the leaks are, including garages and crawl spaces |
| Supply | Outdoor air ducted to the return side of the central air handler for filtering, conditioning and distribution | Uses existing ducts; can pressurise the house slightly |
| Balanced, HRV or ERV | Supplies and exhausts equal volumes through a heat exchanger | Highest cost; controlled air paths and energy recovery |
For how ventilation fits into HVAC more broadly, see what ventilation means in HVAC.
HRV or ERV
The choice turns on moisture, which is why climate matters more than brand.
- HRV recovers heat but passes moisture straight out with the exhaust. In a cold climate where winter indoor air tends to be too humid, removing moisture is useful.
- ERV transfers moisture as well as heat. In winter it retains some indoor humidity; in humid summers it keeps some outdoor moisture from coming in.
Building America’s example is Florida: indoor air in conditioned homes “is generally cool and dry” while outdoor air “is quite humid”, so with an ERV “the incoming air will be somewhat cooled and dehumidified.” It also notes that “the recommendations vary from manufacturer to manufacturer”, which is honest: there is no single rule for every climate.
An ERV reduces the moisture load the ventilation air adds; it does not remove moisture already in the house. In a humid climate with a damp house, the fix is still the air conditioner or a dedicated dehumidifier. If the house is cold and clammy, the cause is usually elsewhere; see a house that is cold but humid. If it is too dry in winter, see whole-house humidifiers.
Installation and upkeep
- Balance the flows. A balanced system that is not commissioned is not balanced.
- Clean or replace filters on both air streams, typically every few months.
- Clean the core as the manufacturer directs; HRV cores are usually washable, many ERV cores are not.
- Keep intake and exhaust terminations apart and clear of snow, leaves and dryer vents.
- Frost control in very cold climates, which is built into most units.
Mechanical ventilation belongs in the same conversation as air sealing: see why envelope work comes first.
Frequently asked questions
What is the difference between an ERV and an HRV?
Both bring in outdoor air and exhaust indoor air through a heat exchanger. HRVs transfer sensible heat only and do not transfer moisture; ERVs transfer both heat and moisture, per the Department of Energy’s Building America guidance.
Does my house need mechanical ventilation?
If it is tight, code likely requires it. Building America summarises residential code as requiring whole-house mechanical ventilation for dwellings with air leakage below 5 air changes per hour at 50 pascals when tested with a blower door. Older, leakier houses are ventilated, unevenly, by their leaks.
Should I get an ERV or an HRV?
It depends mainly on climate and indoor moisture. HRVs suit cold climates where winter indoor air tends to be humid; ERVs retain winter humidity and reduce summer moisture intake in humid climates. Building America notes recommendations vary by manufacturer.
Does an ERV dehumidify?
Not in the sense a dehumidifier does. It reduces the moisture carried in by ventilation air in humid weather, but it does not remove moisture already in the house. Humidity control still depends on the air conditioner or a dehumidifier.
Methodology and limitations
Definitions and code summaries are quoted from the Department of Energy’s Building America Solution Center, which cites the International Residential and Mechanical Codes. Ventilation rates are set by ASHRAE 62.2, a private standard we name but do not reproduce.
- Local code adoption and amendments govern what is required in your jurisdiction.
- We publish no installed prices or energy savings figures, because neither is federally measured.
- Equipment selection for a specific house needs a ventilation design, not a rule of thumb.
Sources
- US Department of Energy, Building America Solution Center, Whole House Ventilation Strategies for Existing Homes.
The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.
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