HRV Units and the Passive House

Wondering how a PassiveHouse achieves such exceptional air quality and efficiency? It’s a good time to explain the HRV.

Heat recovery unit for the EkoBuilt Model Home

Zehnder Novus 300 – used in the EkoBuilt Model Home

A passive house is able to perform so effectively on very little energy in large part due to its exceptional air-tightness.  This very air-tightness, however, makes the need to introduce fresh air into the home all the more critical. This is achieved through an HRV Unit (heat and energy recovery ventilation unit) which draws fresh air into the home, filtering for pollen and other irritants and contaminants, and then exhausting used air while recovering the heat from that air.

With building standards generally improving year on year, HRV Units are now more common in conventional homes than ever. Most new homes in Ontario and elsewhere in Canada are now required to include an HRV. The difference between these units and the ones employed in a PassiveHouse build is the rated efficiency.

EkoBuilt’s Model Home is using a Zehnder Novus 300 HRV, which operates at 92% efficiency. This is extremely favourable in comparison to the 65% efficient units installed in most conventional homes. For a quick overview of how a home uses an HRV (in this case another model from Zehnder), this is a good video to check out:


A key indicator to be aware of is ACH or Air Changes per Hour. This is the number of times in an hour that a home refreshes its entire volume of air. Conventionally built homes tend to average a rate of 4-10, while Energy Star homes have an ACH of 2.5, R2000 homes average 1.5 ACH, and a PassiveHouse just 0.6 ACH.

Air Changes Per Hour by House Construction Standard

Conventional Homes: 4-10 ACH
Energy Star: 2.5 ACH
R2000: 1.5 ACH
PassiveHouse: 0.6 ACH

Keeping ACH at or under 0.6 is important, as it means that no condensation will form within wall or roof cavities. It’s very important for builders to be aware that insulation only performs to rating if ACH is kept to this low level.

Can a building be too air-tight?

All of this might leave you wondering whether the degree of air-tightness in a PassiveHome is healthy. The short answer is a resounding YES.

A home built to the PassiveHouse standard makes sure that both the home and its inhabitants are ‎healthy. As noted above, the reduced risk for condensation keeps air quality strong, while an ample amount of fresh air keeps the home’s residents healthy and feeling good. PassiveHouse is designed to provide each person with 30 cubic meters of fresh air per hour through a 92% efficient HRV.

How does the EkoBuilt Model Home Perform?

Blower door test results 0.53 ACH

Blower door results for the EkoBuilt Model Home

Just over a week ago we conducted the first tests on air pressure for the EkoBuilt Model Home that we’re building. Preliminary results were 0.53 ACH (air changes per hour), which is under the 0.6 benchmark for PassiveHouse construction.

After insulation and drywall, we hope that we’ll be able to improve further on this number. Stay tuned!

If you’d like to find out more about this or any other aspect of PassiveHouse construction and performance, please contact us.

EkoBuilt partners with CoolHeat Comfort Systems for the provision of the HRV units. CoolHeat Comfort Systems is a local family run HVAC Company in Ottawa providing HVAC services such as installations, maintenance, repairs and upgrades.

2 thoughts on “HRV Units and the Passive House

  1. Pingback: Your questions answered! | EkoBuilt

  2. Pingback: Home energy and design blog by EkoBuilt, Ottawa custom home builder

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