Quick answer
An energy recovery ventilator (ERV) is a balanced ventilation unit that exchanges stale indoor air for fresh outdoor air through a core that transfers both heat and water vapor between the two streams, so incoming air arrives closer to indoor temperature and humidity than it would through a plain fan.
Moving moisture as well as heat is what separates an ERV from an HRV. In humid summers it keeps some outdoor moisture out; in dry winters it keeps some indoor moisture in.
Quick facts
The key facts about Energy Recovery Ventilator (ERV), with sources:
- Transfers
- Sensible heat and latent heat (moisture) 1
- Core types
- Permeable membrane plate or rotating enthalpy wheel
- Recovery effectiveness
- Recovering latent heat typically gives higher total effectiveness than sensible only 1
- Efficiency metric
- HVI-certified ratings, including ASRE 4
- Ventilation standards
- ASHRAE 62.2-2025 (homes), 62.1-2025 (commercial) 2
- Not a dehumidifier
- Limits moisture brought in; does not remove indoor moisture by itself
Key takeaways
- An ERV ventilates and recovers both heat and moisture; an HRV recovers heat only 1.
- In humid climates, an ERV cuts the moisture that fresh air would otherwise add, easing the air conditioner’s job.
- In very dry winters, it keeps some indoor humidity in.
- It is not a dehumidifier. If indoor air is already too humid, an ERV alone will not fix it.
- Size airflow to ASHRAE 62.2 and compare HVI-certified ratings 2 4.
What an ERV does
Tight homes need planned fresh air. ASHRAE 62.2-2025 sets minimum ventilation for dwellings 2. Bringing in outdoor air costs energy, because that air must be heated, cooled, dried or humidified. An ERV recovers part of that energy.
Like an HRV, an ERV runs two air streams through a core without mixing them. The difference is the core.
An ERV core lets water vapor pass between streams, either through a special membrane or on a rotating wheel coated with a moisture-holding material.
Natural Resources Canada notes that recovering latent heat as well as sensible heat typically gives higher total recovery effectiveness 1.
The word "enthalpy" in "enthalpy core" or "enthalpy wheel" refers to total heat: temperature plus moisture.
How an ERV works on a humid summer day
- Hot, humid outdoor air → enters the core
- Cool, drier indoor exhaust air → enters the core in separate passages
- Heat and some water vapor move from outdoor air to exhaust air → fresh air arrives cooler and drier
- Exhaust carries that heat and moisture outside
- Air conditioner handles the rest of the load → less work than with no recovery
An ERV in winter: holding humidity in
In cold weather the roles flip. Indoor air is the warm, moist stream and outdoor air is cold and very dry.
The ERV core passes some of the indoor moisture back to the incoming air instead of sending it all outside.
In a dry climate or a very tight home, that can keep indoor humidity from dropping to uncomfortable levels without running a humidifier as often.
That same effect can be a drawback in a home that already has too much winter moisture, for example from many occupants, cooking or drying clothes indoors. There, holding moisture in can lead to condensation on windows. Such homes often do better with an HRV, which exhausts the moisture while still recovering heat.
This is why the ERV-or-HRV choice is less about the product and more about the house and climate. A designer looks at both summer and winter conditions before choosing.
ERV core types
| Core | How it moves moisture | Typical use | Notes |
|---|---|---|---|
| Membrane plate (fixed) | Water vapor passes through a permeable membrane | Most homes | No moving parts in the core |
| Enthalpy wheel (rotary) | Wheel picks up heat and moisture in one stream, releases in the other | Larger and commercial systems | Moving part; small cross-leakage possible |
| Ductless through-wall ERV | Small ceramic or membrane cores | Single rooms, retrofits | Often installed in pairs |
ERV vs HRV: which one fits your home
| Question | ERV | HRV |
|---|---|---|
| Recovers moisture? | Yes, partly | No 1 |
| Best climate | Humid summers; very dry winters | Cold winters with indoor moisture to remove |
| Summer effect | Brings in less moisture | Brings in outdoor moisture |
| Winter effect | Keeps some indoor moisture | Exhausts more indoor moisture |
| Condensate drain | Often not needed (check maker) | Usually needed |
| Related | Demand-controlled ventilation, dehumidification | Ventilation rate |
Example: moisture an ERV keeps out in a humid summer
A home ventilates 60 CFM. Outdoor air holds 0.0160 lb of water per lb of dry air (a muggy summer day); indoor air holds 0.0093 (about 50% relative humidity at 75°F).
Latent load ≈ 4,840 × CFM × difference in humidity ratio (a standard HVAC engineering approximation). The ERV’s 50% latent recovery is an example figure; check certified ratings.
| Case | Math | Latent load from ventilation |
|---|---|---|
| No recovery | 4,840 × 60 × (0.0160 − 0.0093) | about 1,950 BTU/h |
| ERV at 50% latent recovery | 1,950 × (1 − 0.50) | about 975 BTU/h |
| Moisture load avoided | 1,950 − 975 | about 975 BTU/h, roughly 0.08 ton of AC |
That moisture would otherwise have to be removed by the air conditioner or a dehumidifier. In a humid climate it is a real share of a small home’s latent load. An HRV in the same case would recover some sensible heat but none of this moisture.
Where ERVs are used
- In tight new homes in humid or mixed climates.
- In homes with very dry winters, to keep indoor humidity from falling too low.
- In commercial buildings, where large outdoor air loads make energy recovery common.
- On the HVI-Certified Products Directory 4.
- In ventilation upgrades; see ERV and HRV services.
Benefits and trade-offs
Benefits
- Fresh air with less added moisture in humid weather.
- Keeps some humidity in during dry winters.
- Recovers more total energy than heat-only recovery in many conditions 1.
- Balanced airflow; no depressurizing the house.
Trade-offs
- Not a dehumidifier; indoor moisture sources still need exhaust.
- Cores need cleaning; some membranes cannot be washed with water.
- In homes with high indoor winter humidity, an HRV may remove moisture better.
- Fan energy, ducts and space required.
What an ERV cannot do
An ERV moves moisture toward the drier stream. It cannot pull the house below outdoor humidity. On a muggy day it reduces how much moisture fresh air adds; it does not dry an already damp house. In humid climates, pair it with an air conditioner set up for moisture removal or a whole-home dehumidifier.
It also should not replace bathroom and kitchen exhaust. Those spot fans remove moisture and odors at the source; an ERV handles whole-house fresh air.
Cost drivers and lifespan
Cost depends on airflow capacity, core type, duct layout, wall or roof penetrations, controls and electrical work. Tying into existing HVAC ducts is usually simpler than running dedicated ducts.
HyreHVAC publishes no prices without enough dated quotes. See indoor air quality services for typical scope.
How an ERV is designed and installed
- Set required airflow from ASHRAE 62.2 or local code 2.
- Decide ERV vs HRV based on climate and indoor humidity.
- Choose a unit with HVI-certified ratings at that airflow 4.
- Plan ducts: fresh air to bedrooms and living areas; exhaust from baths, kitchen or a central return; outdoor hoods well apart.
- Install, interlock with the HVAC fan if shared, and balance supply and exhaust.
- Measure airflow; RESNET/ICC 380 covers ventilation airflow testing 5.
Maintenance
- Clean or replace filters per the maker, often every few months.
- Clean the core as directed; many membrane cores should be vacuumed, not washed.
- Clear outdoor hoods of leaves, snow and nests.
- Check that dampers and controls work each season.
Warning signs
- Rising indoor humidity in summer: check AC moisture removal and ERV airflow.
- Stuffy rooms or odors: ventilation may be too low or out of balance.
- Ice in the core in extreme cold: check frost control.
- Noisy fans or rattling: call a ventilation contractor.
Standards and codes
ASHRAE 62.2-2025 covers home ventilation and 62.1-2025 covers commercial buildings; the 2025 edition of 62.1 adds demand-control ventilation sequences 2. Commercial energy codes such as ASHRAE 90.1 can require energy recovery for some large outdoor air systems; check the edition your state uses 3 6.
RESNET/ICC 380 covers measuring ventilation airflow 5, and HVI certifies ERV ratings 4.
Misconceptions
- Myth An ERV dehumidifies my house.
- Reality It limits moisture brought in; it does not remove existing indoor moisture.
- Myth ERVs only work in summer.
- Reality They also hold indoor moisture in dry winters.
- Myth ERV and HRV are interchangeable.
- Reality Climate and indoor humidity decide which fits 1.
- Myth An ERV replaces bath fans.
- Reality Spot exhaust still matters.
Climate decides ERV vs HRV
Humid states such as Florida, Georgia, North Carolina and much of Texas lean toward ERVs to limit summer moisture. Very dry winter climates can also favor ERVs to keep indoor humidity up. Cold, moderately dry winters, as in parts of Washington and Ohio, often suit HRVs.
Do you need an ERV?
Consider one if your home is tight and you live with humid summers, or if winter air gets uncomfortably dry. If summer humidity is already high indoors, fix moisture removal first, then add ventilation.
Next step: read indoor air quality basics and ask about ventilation options for your home.
Questions about Energy Recovery Ventilator (ERV)
What does an energy recovery ventilator do?
An ERV replaces stale indoor air with fresh outdoor air at a balanced rate, and its core transfers both heat and moisture between the two air streams. In summer it sends some incoming heat and humidity back out; in winter it keeps some indoor heat and humidity in.
Is an ERV or an HRV better?
It depends on climate. An ERV transfers heat and moisture; an HRV transfers heat only. ERVs suit humid summers and very dry winters. HRVs suit cold climates where homes have extra winter moisture to remove. Indoor humidity and household habits also matter.
Does an ERV dehumidify?
Not by itself. An ERV reduces the moisture that fresh air brings in during humid weather, but it cannot make indoor air drier than outdoor air. To remove moisture already in the house, you need an air conditioner set up for it or a dehumidifier.
Do ERVs need a condensate drain?
Many do not, because the core moves moisture as vapor instead of condensing it. Some conditions and models still produce condensate. Follow the maker’s instructions; HRVs usually do need a drain.
How do you clean an ERV core?
Follow the maker’s manual. Many membrane cores should be vacuumed gently rather than washed, because water can damage the membrane. Filters should be cleaned or replaced every few months. Wheels in larger systems need periodic service by a technician.
How much ventilation does an ERV provide?
Enough to meet ASHRAE 62.2 or your local code, which sets airflow by house size and number of bedrooms. The ERV should be sized and balanced for that airflow, then measured after install. Too much ventilation wastes energy.
Can an ERV help with wildfire smoke?
Only if it has good filters and you can reduce or stop outdoor air during smoke events. Bringing in smoky air defeats the purpose. Many units allow recirculation or reduced airflow. See our wildfire smoke and filters research for filter guidance.
What is an enthalpy wheel?
An enthalpy wheel is a rotating ERV core coated with a material that holds heat and moisture. As it turns, it picks up heat and water vapor from one air stream and releases them into the other. Wheels are common in larger and commercial systems.
Does an ERV save energy?
It reduces the energy needed to condition fresh air, because the incoming air arrives closer to indoor temperature and humidity. The fans use some electricity, so net savings depend on climate, airflow and the unit’s certified efficiency. Compared with ventilating through a plain fan, recovery usually cuts the load.
Sources
- Natural Resources Canada, CanmetENERGY fact sheet: Reducing Energy Waste with Heat Recovery, retrieved .
- ASHRAE, Standards 62.1 and 62.2 (2025 editions), retrieved .
- ASHRAE, Standard 90.1 Energy Standard for Sites and Buildings Except Low-Rise Residential, retrieved .
- Home Ventilating Institute (HVI), Publications (ASRE consumer and builder guides), retrieved .
- RESNET, HERS Index (references ANSI/RESNET/ICC 380), retrieved .
- U.S. DOE, Building Energy Codes Program, retrieved .
Expert review
Written by the HyreHVAC Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: ERV and HRV definitions from NRCan; standards from ASHRAE and RESNET pages; ratings from HVI. The humid-summer example uses a standard latent-load approximation and a labelled example recovery rate.
Suggest a correction. We fix errors and say what changed.