Zehnder ComfoSystem HRV/ERV and the Ontario Building Code (with practical download: HRAI Design Summary)


So you are building a high performance home, well insulated, very airtight, with a very small heating/cooling system. That is great and the Zehnder ComfoSystem is the perfect match for your house. Energy efficient, quiet, easy and fast to install, easy to clean, hypoallergenic.

But what about the Ontario Building Code [OBC]? How can you use the Zehnder ComfoSystem in Ontario?

The following is a quick summary of what you need to keep in mind when designing or spec'ing a Zehnder ComfoSystem in Ontario.

Zehnder designs to ASHRAE 62.2. The ventilation rates that the OBC stipulates are a bit different than that. The ventilation rates used by Zehnder are:

  • Exhaust Kitchen: 36cfm

  • Exhaust Bathroom: 24cfm

  • Exhaust Half Bathroom ("Powder Room", "Water Closet Room"): 12cfm

  • Supply: divided up to all the other rooms (most of the time 24cfm per bedroom, other rooms on a need basis).

These rates work very well with passive house and often result in whole house ventilation rates close to 0.3ACH.

The OBC prescribes the following ventilation rates (Table

  • Supply Master bedroom: 10 L/s (36cfm)

  • Supply Other bedrooms, living room, dining room, family room, recreation room, other habitable rooms, (laundry room, utility room): 5 L/s (18cfm)

  • Exhaust Kitchen, bathroom or water closet room: 5L/s (18cfm)

  • Exhaust Basement: 10L/s (for a single open room, with some other stipulations once you divide the space up)

Exhaust fan capacity for the entire dwelling is also set in Table, but with a balanced ventilation system such as the Zehnder ComfoSystem, you will generally sit much above the minimum required amounts by the OBC.

Overall, the rates a bit different, but can still be accommodated by a Zehnder ComfoSystem. There is also no talk in the OBC about boost rates.

Interior Intake and Exhaust Locations

  • Ceiling mounted, or

  • not more than 30mm from the ceiling

Outdoor Intake and Exhaust Locations

  • Intake minimum 450mm of the ground or the depth of expected snow accumulation

  • minimum 900mm away from potential sources of contaminants (gas vents or oil fill pipes)

  • Exhaust minimum 100mm of the ground (which we will never recommend)

Duct types and sizing are also covered by the OBC, but have to be looked at on a project to project basis. The code is very prescriptive about duct sizing, but is not really dealing with systems such as the Zehnder, which use multiple duct runs to single outlets. I would recommend talking to the inspector in charge and explaining how the system comes together.

 HRAI Design Summary (click to download)

HRAI Design Summary (click to download)

To apply for your building permit

In order to apply for your building permit according to Part 9 of the OBC, the HRAI has created a design summary, which comes in very handy.

Download the HRAI summary to apply for your building permit right here.

So now it's your turn. Tell us about your projects, or challenges you have in adapting a whole house ventilation system to your high performance home or passive house.

Email us or comment below.