HRV Selection Guide for Ontario Homes: SRE at -25°C, SB-12 Compliance, and What the MVDS Requires
Selecting an HRV or ERV for an Ontario home is no longer an afterthought — under OBC 2024 the selected unit must be documented in the Mechanical Ventilation Design Summary (MVDS) before the building permit is issued. That documentation must show the specific model, its ventilation capacity, its Sensible Recovery Efficiency (SRE) at -25°C from certified test data, and the SB-12 compliance path the home is following. Selecting a unit that passes on paper but underperforms in real conditions adds defrost cycling, reduced ventilation delivery, and increased operating cost.
This guide explains the three key selection criteria for Ontario HRVs — ventilation capacity, SRE at -25°C, and SB-12 compliance — and how each criterion changes by climate zone. For the MVDS as a permit document, see our MVDS guide. For the complete HRV/ERV design service, see our HRV/ERV design service.
CAN/CSA-F326 — the standard the MVDS documents compliance with — establishes three primary criteria for HRV and ERV selection in Ontario residential buildings. All three must be satisfied and all three must be documented in the MVDS.
1. Ventilation Capacity (L/s)
The HRV or ERV must deliver a minimum ventilation rate in litres per second (L/s) based on the home's floor area and occupancy, as determined by CAN/CSA-F326. This is the total fresh air supply rate — the amount of outdoor air the unit delivers to the home under normal operating conditions. The MVDS must confirm the selected unit's rated capacity meets or exceeds the calculated minimum for the specific home. A unit sized too small for the floor area fails this test even if its SRE is excellent.
2. SRE at -25°C
The Sensible Recovery Efficiency at -25°C is the HRV's thermal efficiency at the coldest standard test condition under CAN/CSA-F326. It measures how much of the outgoing warm air's heat is recovered and transferred to the incoming cold air at -25°C outdoor temperature. A high SRE at -25°C means less heat is lost, less backup electric heat is needed to preheat incoming air, and defrost cycles are shorter and less frequent. This number must come from certified test data — not marketing materials. For Zone 6 and Zone 7, SRE at -25°C is directly relevant to real-world winter performance.
3. SB-12 Compliance Path
Ontario's Supplementary Standard SB-12 sets energy efficiency requirements for residential buildings. For ventilation, SB-12 specifies minimum SRE thresholds for HRVs depending on the compliance path the home is following — prescriptive paths have specific SRE minimums, while performance paths may allow different approaches. The MVDS must identify the SB-12 compliance path and confirm the selected HRV meets the SRE threshold for that path. A unit selected without reference to SB-12 may pass the F326 capacity test but fail the SB-12 energy efficiency requirement.
Many HRV installations satisfy the ventilation capacity requirement but use units with low SRE at -25°C — units that are inexpensive, widely available, and well-known but designed for milder climates. In Zone 6 at -24°C and Zone 7 at -28°C, a low-SRE HRV defrost-cycles frequently during the coldest months, delivering reduced ventilation during the periods when outdoor air infiltration is already lowest. The MVDS requirement under OBC 2024 forces the SRE question to be answered before the permit is issued — not after the unit is installed. Selecting a unit with genuine high SRE at -25°C from certified test data is the correct approach for all Ontario zones. See our HRV/ERV design service.
The choice between an HRV (Heat Recovery Ventilator) and an ERV (Energy Recovery Ventilator) is one of the most common questions in Ontario residential ventilation design. The difference is in what they recover: an HRV recovers sensible heat only; an ERV recovers both sensible heat and latent energy (moisture). For most Ontario climates, the HRV is the more appropriate choice — and the MVDS must document whichever is selected.
| Factor | HRV | ERV |
|---|---|---|
| Heat recovery | Yes — sensible heat | Yes — sensible + latent |
| Moisture recovery | No — exhausts moisture with stale air | Yes — retains indoor humidity |
| Best for cold winters | Yes — prevents over-humidification | Risk of frost at -25°C and below |
| Best for humid summers | Passes summer humidity in | Reduces summer humidity load |
| Ontario recommendation (Zone 6/7) | Preferred for most homes | ICF / very tight homes with low humidity |
| SRE at -25°C requirement | Applies directly — key metric | Applies — also check total energy efficiency |
Ontario winters — particularly in Zone 6 and Zone 7 — produce interior relative humidity that naturally stays moderate in well-ventilated homes. An HRV's exhaust of indoor moisture prevents the over-humidification that can cause condensation on windows and walls during the coldest months. ERVs, which retain indoor moisture, can create over-humidification problems in tightly built homes in Zone 6 and Zone 7 winters. The exception is extremely tight, very well-insulated homes — typically ICF construction — where indoor humidity during winter may be chronically low and moisture retention is beneficial. For most Ontario custom homes, an HRV with high SRE at -25°C is the correct choice.
The relevance of SRE at -25°C varies by climate zone — in Zone 7 it is the single most important HRV selection criterion; in Zone 5 it matters but is less critical.
Zone 5 — -18°C
At -18°C the HRV rarely operates at or below the -25°C test condition. SRE at -25°C still matters for the MVDS and SB-12 compliance — but a unit meeting the minimum SB-12 SRE threshold is typically adequate. The performance gap between a high-SRE and standard unit is less impactful in Zone 5 real-world operation than in colder zones. See our Aurora and Newmarket guides.
Zone 6 — -22°C to -24°C
In Zone 6 the -25°C test condition is closely approached on the coldest nights. A low-SRE unit will defrost more frequently during January and February — reducing ventilation delivery and increasing supplemental electric heat use during the coldest period. Specifying a unit with genuine high SRE at -25°C from certified test data is the right approach for all Zone 6 projects. See our Barrie and Collingwood guides.
Zone 7 — -28°C
In Zone 7 outdoor temperatures regularly exceed the -25°C test condition. SRE at -25°C is the most directly relevant performance metric. A low-SRE HRV in Muskoka will defrost-cycle continuously during cold snaps, potentially delivering almost no net ventilation at the times when airtight construction most needs it. High-SRE selection is not optional in Zone 7 — it is the primary selection criterion. See our Muskoka guide.
What is SRE at -25°C and why does it matter for Ontario?
SRE (Sensible Recovery Efficiency) at -25°C is the HRV's thermal efficiency at the coldest standard test condition under CAN/CSA-F326. It measures how much heat the unit recovers from exhaust air and transfers to incoming fresh air at -25°C outdoor temperature. In Zone 6 and Zone 7 Ontario, this temperature is approached or exceeded during winter cold snaps — making the -25°C SRE a directly relevant real-world performance metric, not just a paper specification. High SRE at -25°C means less heat loss, fewer defrost cycles, and better ventilation delivery during the coldest months.
Does the MVDS require me to select a specific HRV before submitting my permit?
Yes — the MVDS must document the specific HRV or ERV model (manufacturer and model number), its ventilation capacity, and its SRE at -25°C from certified test data. This means the equipment selection must be made before the permit application is complete. "HRV to be determined" is not an acceptable MVDS entry. The OBC 2024 requirement brings HRV selection into the permit documentation stage. See our MVDS guide.
Should I choose an HRV or ERV for my Ontario home?
For most Ontario custom homes — particularly in Zone 6 and Zone 7 — an HRV is the preferred choice. Ontario's cold, dry winters mean that an HRV's exhaust of indoor moisture helps prevent over-humidification and condensation on cold surfaces. An ERV's moisture retention can cause humidity problems in tightly built homes during Zone 6 and Zone 7 winters. The exception is very tight, high-performance homes — often ICF construction — where indoor humidity in winter may be chronically low and an ERV's moisture retention is beneficial. Confirm with your designer based on your specific home's airtightness target.
What is SB-12 and how does it affect HRV selection?
SB-12 is Ontario's Supplementary Standard for energy efficiency in residential buildings. For ventilation, SB-12 sets minimum SRE thresholds for HRVs depending on the compliance path the home is following. The MVDS must identify the SB-12 compliance path and confirm the selected HRV meets that path's SRE threshold. An HRV that meets the F326 capacity requirement but falls below the SB-12 SRE threshold for the chosen compliance path is non-compliant. Our MVDS includes SB-12 compliance path documentation as a standard component.
Need an HRV selected and an MVDS produced? We select the right unit for your zone, confirm SRE at -25°C from certified data, document the SB-12 compliance path, and produce the MVDS — BCIN-stamped, included in every permit package. 48 hours.
Get Free Quote →We select the right HRV or ERV for your climate zone and home size, confirm the SRE at -25°C from certified test data, identify the SB-12 compliance path, and produce the complete MVDS — BCIN-stamped and ready for your Ontario building permit application. Included as standard in every complete permit package alongside the CSA F280 heat loss, mechanical drawings, and Schedule 1. See our HRV/ERV design service and our MVDS guide.
- HRV or ERV selected for your climate zone and home size
- SRE at -25°C confirmed from certified CAN/CSA-F326 test data
- Ventilation capacity verified against F326 minimums
- SB-12 compliance path identified and documented
- MVDS produced · BCIN-stamped · 48h delivery · OBC 2024