A heat recovery ventilator (HRV) brings fresh air in from outside and sends stale air out. An energy recovery ventilator (ERV) does the same. They differ in what they recover from the air going out. This guide explains how each one works and why whole-house ventilation is needed. It covers the ventilation standard that many codes and programs reference. It also explains how to choose by climate and how to read efficiency ratings. Most of the detail comes from the Building America Solution Center (BASC) of the U.S. Department of Energy (DOE). Pacific Northwest National Laboratory publishes BASC for DOE. The BASC guides we used were last updated in 2017 and 2018.
Why whole-house ventilation matters
The U.S. Environmental Protection Agency (EPA) covers this on its indoor air quality page. It says, "Most home heating and cooling systems, including forced air heating systems, do not mechanically bring fresh air into the house." It adds that advanced designs of new homes are starting to use mechanical systems that bring outdoor air into the home. It says some of these designs include energy-efficient heat recovery ventilators, also known as air-to-air heat exchangers.
A 2018 BASC guide says kitchen and bath fans "provide intermittent ventilation to remove contaminants near the source." By contrast, it says whole-house ventilation is meant to run continuously (or at automated intervals). Its job is to dilute possible contaminants across the whole house.
How HRVs and ERVs work
The 2018 BASC guide says HRVs and ERVs "are balanced systems." It says this means they exhaust air and supply outdoor air at the same time and at very similar rates. The two airstreams cross in a heat exchanger. In winter, "much of the heat in the exhaust stream is transferred to the supply stream (the reverse is true in the summer)." BASC says, "HRVs transfer sensible heat only; ERVs also transfer moisture (latent heat)."
A 2017 BASC guide for new homes says the main difference is that "an ERV is able to transfer moisture as well as heat from the more humid air to the drier air." The 2018 guide adds that ERVs and HRVs "may be connected to the home’s central air handler and duct system or independently ducted."
| HRV | ERV | |
|---|---|---|
| Airflow | Balanced: brings in and exhausts air at very similar rates | Balanced: brings in and exhausts air at very similar rates |
| What crosses the heat exchanger | Heat only (sensible heat) | Heat and moisture (latent heat) |
| Example BASC gives | Can help reduce indoor humidity in very airtight cold-climate homes where it is uncomfortably high | May be a better choice where it is usually too humid outdoors |
ASHRAE 62.2, EPA Indoor AirPlus and building codes
The 2018 BASC guide says ASHRAE Standard 62.2 sets minimum requirements for adequate home ventilation. It says many codes and programs reference this standard for indoor air quality requirements. We did not review the ASHRAE standard itself.
EPA describes Indoor AirPlus as "a voluntary partnership and labeling program" for new home builders. Its construction specifications are dated December 2025. They require certified homes to "Provide mechanical whole-dwelling ventilation meeting all requirements of ASHRAE 62.2-2010 or later."
For building codes, BASC gives a second-hand summary. The 2018 BASC guide says one of its sections is excerpted from an ASHRAE indoor air quality guide (Schoen et al. 2018). In that section, it says, "The 2012, 2015, and 2018 [International Residential Code] require whole-house mechanical ventilation for relatively air-tight homes." We did not review the code text. The excerpt also does not cover the 2021 or 2024 editions.
The same excerpt explains that local codes can lag. It says it can take time for the model codes to adopt the rates published in ASHRAE Standard 62.2. It can take even more time for local jurisdictions to adopt the model codes. Jurisdictions also sometimes edit the model codes before adopting them. As a result, it says, 62.2 rates "are often higher than those required by local codes." BASC also warns, "Achieving AHSRAE 62.2 ventilation requirements in existing homes may increase the moisture content in the indoor space, in humid climates." (BASC spells ASHRAE "AHSRAE" here.)
How to choose between an ERV and an HRV
The 2018 BASC guide says the choice is not always straightforward. It says the key question to ask is whether it is usually too humid outdoors. If so, it says, an ERV may be a better choice.
BASC uses Florida as its hot-humid example. It says, "In Florida, for example, air inside conditioned homes is generally cool and dry. Outdoor air is quite humid." Incoming air passing through an ERV "will be somewhat cooled and dehumidified." BASC then adds, "This does not mean an ERV dehumidifies the home." Running an ERV raises indoor humidity, "but the humidity increase will be less than if a different ventilation strategy was used." Our guide to indoor humidity covers humidity targets and dehumidifiers.
BASC says that "Outside of hot, humid climates, selecting ERVs or HRVs is not as straightforward." It notes that manufacturer recommendations and maps "vary from manufacturer to manufacturer." Its examples include:
- Older homes in cold climates. Winter air is often "uncomfortably dry," and "An ERV can help retain moisture within the home and potentially improve comfort."
- Very airtight homes in cold climates. In smaller homes with lots of moisture generation, "an HRV can help reduce indoor humidity."
- Hot, dry climates. "Larger or leakier homes with low moisture generation may benefit from ERVs," while "smaller, tighter homes with higher occupancy may benefit from HRVs."
- Mixed climates. "An ERV may be more beneficial during the cooling season and an HRV might be more appropriate during the heating season."
BASC says, "There is not a hard-and-fast rule about which type of system is more appropriate." The 2017 new-homes guide advises checking "the manufacturers' specifications for determining which model is best in which climate," especially "in regard to ERVs in humid climates."
ENERGY STAR's fan specification excludes HRVs and ERVs ducted to the ventilated space
ENERGY STAR's ventilating fan specification is Version 4.2 (Rev. April 2024). It lists "Heat/energy recovery ventilation fans ducted to the ventilated space" among product types that "are not eligible for ENERGY STAR." We found no separate U.S. ENERGY STAR category for HRVs or ERVs.
The specification does cover other fans. ENERGY STAR's partner page says, "In-line fans designed to be installed as supply fans can now certify as ENERGY STAR." Its consumer page says certified ventilation fans "use about 48% less energy than standard models."
HVI ratings: what to look for
The 2018 BASC guide says, "The Home Ventilating Institute (HVI) publishes standards for testing and rating the efficiencies of ERVs and HRVs." It says Apparent Sensible Effectiveness (ASEF) is the most commonly published rating for heat recovery in cold weather. It says to "Look for ASEF values above 80%" and that "the most efficient systems have values above 90%." It adds that Total Recovery Efficiency (TRE) is listed for ERVs. TRE accounts for sensible and latent heat recovery during the cooling season.
HRV and ERV performance figures from a 2018 DOE Building America guide
| Typical sensible effectiveness, low end | 55% |
|---|---|
| Typical sensible effectiveness, high end | 95% |
| ASEF to look for: above | 80% |
| ASEF of the most efficient systems: above | 90% |
| Power use of many HRVs and ERVs, low end | 30 watts |
| Power use of many HRVs and ERVs, high end | 200 watts |
BASC says sensible effectiveness "typically ranges from 55% to 95%," and "the higher values typically come with a higher cost." It also says, "More extreme outdoor temperatures mean greater benefits from heat recovery," and "In colder climates, the savings from heat recovery are more pronounced." It gives no savings figure. The guide says, "Power consumption for many HRVs and ERVs ranges from 30 to 200 Watts."
HRV and ERV maintenance
BASC says the maintenance needs of HRVs and ERVs are often more demanding than for other ventilation systems. BASC says, "As always, refer to manufacturer's instructions for proper maintenance." BASC also warns that ventilation systems can depressurize a home by pulling more air out of it than is brought in. It says this includes exhaust-only systems and ERVs and HRVs that are not properly balanced. It says depressurizing the home "can interfere with any natural-draft combustion appliances located in the home."