More than 3,500 heat recovery ventilators installed in Vancouver

Heat recovery ventilator diagram

HRVs can improve indoor air quality, reduce the risk of mold buildup

Since 2008, home builders in the City of Vancouver have been working in the future.

In keeping with the City's building code, they've been installing heat recovery ventilators (HRVs) in all new one- and two-family homes, with more than 3,500 installed since 2008.

The next provincial building code is expected to include air leakage in some manner, and Vancouver specifically requires an air leakage test to be performed on each home.

"We knew as builders gained experience on building airtight, we would be reducing the risk of mold buildup while improving indoor air quality," says Mark Hartman, Vancouver's Green Building Program manager.

Heat recovery ventilators give better air quality and save energy

Traditional home-building relied on natural ventilation from air leakage to ventilate a home. But with tighter envelopes, the structure can become pressurized or depressurized depending on relative temperatures and/or use of one-way ventilation systems such as exhaust fans.

This can draw air into the living space from dirty areas such as the crawl space, compromising air quality. And, it can force moist air into wall assemblies, risking mold.

Tighter envelopes require better approaches to ventilation. "It was a safety precaution," says Hartman of the City's requirement to install HRVs.

HRVs run the exhaust and supply air systems past each other (without mingling the actual air) so that heat is transferred from exhaust air to the incoming air, pre-warming it and reducing energy loss. Properly adjusted and maintained, HRVs maintain a balanced air supply that delivers fresh air to all rooms in the house.

Hartman says the most efficient homes have air tightness levels of one-half to one and a half air changes per hour (ACH). But typical B.C. homes have five to six ACH, and some range up to 12-15 ACH. This negates the benefits of an HRV, and is not only a significant waste of energy, but makes the home uncomfortable in both summer and winter.

"Having 12 air changes per hour is like having a hole two feet across in the wall of your home when you add up all those small leaks everywhere," says Hartman.

Lessons learned, and next steps

Hartman says that after five years of varying quality of installations, the City worked with the Thermal Environmental Comfort Association (TECA) and the Heating, Refrigeration, and Air Conditioning Institute of Canada (HRAI) to identify the key improvements needed:

  1. Installation details: that HRVs are installed in a conditioned space, as opposed to attics or areas where they are difficult to maintain, and that other sources of ventilation, such as kitchen and bathroom fans, are not connected to the HRV.
  2. Education for homeowners: Homeowners need to know the intended function of their HRV and how to maintain it. "It's important to have an education piece so homeowners don't just say, 'I don't know what this is so I'm going to turn it off,'" says Hartman.
  3. Balancing: HRVs must be set to ensure the flow of air in and out of the home is balanced, with a label showing the correct high and low flow rates for the HRV.
  4. Improved HRV efficiency: a minimum of 65 per cent "sensible heat recovery" to ensure higher levels of performance throughout its life.
  5. Proof of air sealing: requiring a checklist similar to the ENERGY STAR® Thermal Bypass Checklist will help ensure homeowners are getting the full benefit of having an HRV installed.
  6. An EnerGuide score prior to construction: "Requiring an EnerGuide score prior to the start of construction, will ensure that the builder has a Certified Energy Advisor onboard to provide advice on how to seal the home. It gives the builder the best chance to look for things they could improve," says Hartman.
  7. TECA or HRAI certification: Builders are required to complete training through TECA or HRAI for HRV installation.

Hartman says builders are adopting the new practices and are improving the quality of installations as they've worked with the City of Vancouver's requirements. He says the next Code will ensure that all the elements of energy efficiency — insulation, air sealing, and ventilation — are working together to achieve a significant improvement in energy savings and homeowner comfort.