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Balanced HRV/ERV

Installed correctly, a whole-house fresh air system with heat recovery can help ensure a healthier and more comfortable indoor environment with optimum efficiency.

For continuous operation, the target ventilation rate for the home shall be based on house size as follows: 50 cfm for up to 1,500 ft², 70 cfm for 1,501 to 2,500 ft², and 100 cfm over 2,500 ft². For intermittent operation, the average air flow shall meet the minimum target ventilation rate specified above (e.g., if the controller operates the air handler fan for a minimum of 20 minutes each hour, then three times the target ventilation air flow is needed).
The ERV/HRV can be connected to the central air handler and use the HVAC ducts for supply air or it can have its own independent supply ducts. Return air intakes can either be individually ducted from several rooms, or ducted from one or more central locations or the ERV/HRV can use the HVAC system returns. All closable rooms should have at least one ducted supply, or one ducted return, or both.
An HRV/ERV that is connected to the central system supply side shall have a damper to keep air from flowing backward through the unit when the ventilator is off. When the exhaust air inlet and the fresh air outlet of a balanced HRV/ERV whole house ventilation system are interconnected to central space conditioning system ducts, an interlock of the central system air handler unit fan with operation of the HRV/ERV fan shall be required to avoid short-circuiting of ventilation air.
Appropriate ventilation equipment shall be selected based on the target ventilation rate and the climate.
Outdoor air shall be filtered with a MERV 11 filter or higher, and the pressure drop across the filter shall match equipment capabilities. The filter shall be installed to be easily accessible by occupants.
The fan shall be oriented so the equivalent length of the duct run is as short as possible. "Equivalent length" shall be calculated in accordance with ANSI/ACCA Manual D Residential Duct Systems.
The exhaust duct outlet vent shall be located on the exterior of the home where it does not direct air flow onto a walkway, and it is situated at least 10 feet from any air inlet.
Outdoor air intakes shall be equipped with screens to keep out insects and debris, integrated with siding and flashed properly to prevent water intrusion, and caulked where the edges of the duct meet the exterior walls or ceilings to limit the infiltration of exterior air into the home.
All duct seams and connections shall be sealed with mastic or UL 181 tape.
Ducts installed outside of the thermal envelope shall be insulated to a minimum of R-8.
The ventilation rate shall be measured using a flow hood, flow grid, or anemometer, in accordance with test procedures listed in ANSI/RESNET/ICC 380-2016, to ensure that the fan is providing the minimum ventilation rate specified above.
All operation and maintenance procedures shall be reviewed with the homeowner (e.g., how and when to change filter).

BASC Guides

Guide describing how to evaluate existing ventilations systems before performing home upgrades.

Guide describing how to select and install whole-house ventilation systems for existing homes.

This guide describes how to install a whole-building ventilation system to provide adequate dilution of indoor air contaminants. 

Tips to Sell Quality Installed Home Improvements

Home Improvement Expert (HIE) is a valuable tool for organizations committed to quality installed work. The following tips help optimize the value of this tool when selling home improvements:

  • Be the Expert: Take advantage of Building America Solution Center comprehensive guidance on ‘Existing Home’ retrofits.
  • Earn Trust: Inform homeowners how your work conforms to U.S. Department of Energy (DOE) world-class expert guidance and recommend homeowners visit the DOE website as evidence these are indeed official best practices.
  • Clarity with Contrast: Tell prospective homeowner clients to compare your expert recommended best practices with other contractors.
  • Ensure Equivalent Pricing: Tell prospective homeowner clients to insist other bids also include DOE checklists to ensure equivalent quality work.
  • Translate Value: Note your company uses DOE HIE Checklists based on world-class expert recommendations for home improvements on all your public-facing communication including websites, advertising, and signage.
  • Create Emotional Experiences: Provide visual evidence contrasting the difference between poor and high quality work such as infrared images for good and bad insulation and air sealing; pre- and post-energy bills following quality installed work; short and long warranties for standard and high-efficiency equipment; and charts showing amounts of contaminants in homes that can be reduced with effective fresh air systems.

Balanced HRV/ERV Background


Contaminants in homes can trigger asthma and allergy attacks as well as other health problems. Whole-house fresh air systems dilute these contaminants. Balanced ventilation systems like heat recovery ventilators (HRVs) and energy recovery ventilators (ERVs) bring in fresh outside air and distribute it throughout the home using either their own dedicated ducts or the home’s central heating and cooling system ducts. While bringing in this fresh air, the ERV/HRV exhausts an equal amount of stale air from the home, ensuring balanced pressures throughout the home. The incoming and outgoing air pass through a heat exchanger where heat is transferred from the warmer air stream to the cooler air stream, thus heating incoming air in the winter and cooling incoming air in the summer. An ERV also transfers moisture.