When do you need an HRV/ERV?
In Ontario, whether you need a heat recovery ventilator (HRV) or energy recovery ventilator (ERV) depends on what you’re building. In most new dwelling units, an HRV/ERV is effectively the standard ventilation approach used to meet Ontario Building Code (OBC) energy-efficiency and ventilation requirements. For some additions to existing homes, an HRV/ERV may not be mandatory — but you will still need a code-compliant mechanical ventilation design (often centered around a “principal exhaust fan”).
The key is understanding the difference between:
New houses / new dwelling units (including many secondary-suite projects that create a new unit), and
Additions to an existing house that don’t create a new dwelling unit.
This article is general information only. Your building permit reviewer (the authority having jurisdiction) has the final say for your specific project.
HRV vs ERV (in plain language)
Both HRVs and ERVs bring in fresh outdoor air and exhaust stale indoor air using a heat exchanger.
HRV (Heat Recovery Ventilator): transfers heat between outgoing and incoming air. Common choice in cold climates.
ERV (Energy Recovery Ventilator): transfers heat and some moisture, which can help manage indoor humidity in certain conditions.
Either way, they’re typically designed to run continuously at a low rate and ramp up when more ventilation is needed.
New houses: expect to need an HRV/ERV
For a new house (a new dwelling unit), your design typically needs to align with OBC requirements and the applicable energy-efficiency pathway (often referenced through SB-12 for housing). In practice, that means your mechanical ventilation strategy commonly includes an HRV or ERV.
In many permit applications, you’ll also need to provide a ventilation design summary as part of the mechanical package, showing how the home will meet the required ventilation rates.
Why it’s treated differently than an addition
New homes are evaluated as a complete system — envelope, airtightness assumptions, heating/cooling design, and whole-home ventilation. A balanced ventilation system like an HRV/ERV is often the clearest way to demonstrate compliance.
Additions: an HRV/ERV may not be mandatory, but ventilation still is
For an addition to an existing house, an HRV/ERV is not always mandatory. However, you still need a mechanical ventilation solution that meets code intent. That typically involves:
Completing the Residential Mechanical Ventilation Design Summary documentation required for your permit package (as applicable), and
Identifying a principal exhaust fan that provides the required ventilation capacity for the project scope.
What is a “principal exhaust fan”?
A principal exhaust fan is the main fan designated to run (often continuously or intermittently as designed) to provide whole-house ventilation.
In many new-home designs, the HRV/ERV serves as the principal exhaust fan.
In some addition scenarios, the principal exhaust fan may be a bathroom exhaust fan — if it’s designed and specified to meet the required rates and controls.
Centralized control requirements
The principal exhaust fan is often required to be controlled from a centralized location (for example, via a central switch). The exact implementation depends on the design and the applicable code path — but the main takeaway is that you can’t treat whole-home ventilation like a “nice to have.” It needs to be intentionally designed and controllable.
Garden suites and laneway suites: typically treated like new dwelling units
If your project creates a new dwelling unit (for example, many garden suites and laneway suites), it’s typically treated more like a new house from a compliance standpoint — which means you should expect an HRV/ERV (or an equivalent compliant whole-home ventilation strategy) to be part of the design.
Important note: “through-the-wall” HRVs/ERVs may not be acceptable
Some through-the-wall ventilation products are marketed as HRVs/ERVs, but not all of them meet the required Canadian safety/listing standards for the conditions they’ll face in Ontario winters.
As your notes mention:
Some products may have a listing, but not at the required low-temperature operating conditions.
Some products may automatically shut off below certain temperatures, which can create a compliance (and indoor air quality) problem if the system can’t deliver the required ventilation when it’s cold.
If you’re considering a compact or through-wall product, confirm its listing, tested temperature range, and how it will perform during cold-weather operation — and make sure your designer can demonstrate compliance in the permit package.
Practical takeaways (what to do next)
If you’re building a new house: plan for an HRV/ERV and include it in your mechanical design documentation early.
If you’re doing an addition: don’t assume you can skip ventilation design — confirm whether your project needs an HRV/ERV or whether a properly designed principal exhaust fan strategy is acceptable.
If you’re creating a new dwelling unit (garden/laneway suite): treat ventilation like a new-home requirement and expect HRV/ERV-level design rigor.
If you’re choosing equipment: avoid “close enough” products — listing and cold-temperature performance matter.
Conclusion
You typically need an HRV/ERV for new dwelling units in Ontario, including many garden suites and laneway suites. For additions, an HRV/ERV may not be strictly mandatory — but a code-compliant ventilation strategy still is, often documented through a mechanical ventilation design summary and a designated principal exhaust fan with proper controls.
If you’re unsure which category your project falls into, the fastest path is to confirm whether you’re creating a new dwelling unit and have your designer map out the ventilation approach before permit submission.
