HRV / ERV Design Ontario: Better Air Starts With Better Planning, Not Bigger Equipment
Since January 1, 2025, an HRV or ERV is mandatory in every new Ontario home under OBC 2024. But the code requirement is the floor — not the goal. This guide explains when HRV makes more sense than ERV, how ventilation ties into increasingly tight Ontario homes, why duct routing matters more than SRE ratings, and what a complete permit-ready ventilation design actually looks like.
If you need the service directly, see our HRV/ERV ventilation design service. If you want to understand what you're ordering and why, keep reading.
For most of the history of Ontario residential construction, ventilation was handled incidentally. Houses leaked. Air moved through gaps. Nobody designed a ventilation system because the house ventilated itself through every crack in the envelope — inefficiently, unevenly, and at enormous energy cost.
That era is ending. Modern energy codes, better air barriers, better windows, and the rise of ICF and Passive House construction have produced homes that are genuinely tight. In a tight home, the air you breathe is primarily the air you've decided to put there. Which means ventilation is no longer incidental — it's mechanical, intentional, and directly responsible for indoor air quality, moisture management, and occupant health.
OBC 2024 caught up to this reality on January 1, 2025. An HRV or ERV is now mandated in every new Ontario home, and the permit package must include a Mechanical Ventilation Design Summary (MVDS) per CAN/CSA-F326. But the code requirement is the minimum. The homes we design for — particularly ICF builds and custom homes in Simcoe County, Georgian Bay, and Muskoka — need ventilation systems designed for actual performance, not just code compliance. The 2026 OBC guide covers the full regulatory framework. This page focuses on making the design decisions that actually produce good air.
Already know you need a ventilation design? Upload your plans — we produce the complete MVDS, TVC calculation, and equipment specification in 48 hours.
Get Free Quote →The same construction improvements that reduce heating loads also reduce natural infiltration. In a well-built Ontario home, this is almost entirely a good thing — with one condition: the mechanical ventilation system has to be designed to compensate for the air exchange that used to happen accidentally.
Moisture Management
In a tight home, occupant-generated moisture — cooking, showers, breathing — accumulates without intentional exhaust. An incorrectly specified or poorly routed HRV can't adequately remove moisture from bathrooms and kitchens, leading to condensation, mould risk, and long-term structural problems. Ventilation design matters most in the places that generate the most moisture.
CO₂ and Pollutant Buildup
A tight home without adequate fresh air supply will see CO₂ levels rise during normal occupancy — particularly in bedrooms overnight. Elevated CO₂ affects sleep quality, cognitive performance, and general wellbeing. The HRV's continuous low-rate operation supplies fresh air to bedrooms and living areas at rates designed to keep CO₂ within healthy limits. Getting those rates right requires a design, not a guess.
Heat Loss From Ventilation
Ventilation is the largest variable heat loss in a tight home — larger than envelope losses in some well-insulated ICF designs. An HRV or ERV recovers 60–80%+ of that heat rather than exhausting it. But recovery efficiency only matters if the system is operating at design airflow. A poorly routed duct system that's never balanced is recovering far less than the nameplate claims. This is where design is doing the real work.
ICF homes are among the tightest in Ontario. The same construction that delivers R-25 effective walls and excellent air sealing also makes deliberate ventilation design non-optional. For the full ICF mechanical strategy — heating, ventilation, and energy performance — icfhome.ca's sustainable home design resource is the most relevant reference for Georgian Bay and Simcoe County builders.
HRV and ERV are often presented as interchangeable products with a minor technical distinction. They're not. The choice between them has real consequences for indoor humidity, comfort, and energy performance — and the right answer depends on your climate zone, house tightness, and occupancy profile.
Recovers heat. Exhausts moisture.
An HRV exchanges heat between incoming fresh air and outgoing stale air through a heat exchanger core, without transferring moisture. Stale humid air goes out; dry fresh air comes in, prewarmed. This is exactly the right strategy for Ontario's cold, dry winters and humid summers — where you want to exhaust excess interior humidity in winter and not import exterior humidity in summer.
- Most appropriate for Zone 6 and Zone 7 Ontario climates
- Controls interior winter humidity by exhausting moisture
- Does not transfer humidity — prevents summer indoor humidity gain
- OBC 2024 minimum SRE: 60% at -25°C for Zone 6, 55% for colder zones
- Best match for most Simcoe County, Georgian Bay, and Muskoka builds
- Preferred for high-occupancy homes with significant moisture generation
Recovers heat and transfers moisture.
An ERV transfers both heat and moisture between incoming and outgoing airstreams. In winter, it retains some interior humidity rather than exhausting it. This can be beneficial in extremely tight, low-occupancy homes where interior relative humidity drops uncomfortably low in winter — but in most Ontario homes, ERV increases the risk of interior humidity problems and is harder to specify correctly.
- May benefit ultra-tight, very low-occupancy homes in very dry conditions
- Retains interior humidity — reduces winter dry air in some applications
- Transfers exterior humidity indoors in summer — careful sizing required
- Requires more precise specification for Ontario's climate swing
- Not the default choice for most Zone 6–7 Ontario residential projects
- Better fit for dry climates or very specific envelope/occupancy profiles
| Factor | HRV | ERV |
|---|---|---|
| Heat recovery | Yes — sensible heat only | Yes — sensible + latent |
| Winter humidity control | Exhausts excess moisture — good for occupied homes | Retains humidity — risk of overwetting in tighter homes |
| Summer humidity | Does not import outdoor humidity | Transfers outdoor humidity in — requires careful sizing |
| Ontario Zone 6–7 fit | Well matched — cold dry winters, humid summers | Requires specific conditions to be beneficial |
| OBC 2024 compliance | Standard path — SRE at -25°C specified in SB-12 | Permitted — Total Energy Recovery (TER) specified |
| Typical Ontario application | Most new homes — default recommendation | Ultra-tight, low-occupancy, specific design conditions |
ERV is often marketed as the premium option — "recovers more energy." For most Ontario homes, that framing is misleading. Recovering humidity in a Zone 6 or Zone 7 climate, in a home occupied by a normal household, creates winter humidity management problems. The "premium" product can produce worse indoor air quality than a correctly specified HRV. The right unit is the one designed for your climate, your envelope tightness, and your actual occupancy — not the one with the best brochure.
An HRV with 80% SRE on the nameplate does not deliver 80% SRE in the house. It delivers whatever efficiency the actual installed system achieves — which is determined by duct layout, duct lengths, leakage, balancing, and maintenance access, not by what's printed on the box.
The ventilation design decisions that actually affect performance in the real home are: where exhaust pickups are located (they should be in the rooms generating the most moisture and pollutants — bathrooms, kitchen, utility room), where fresh air supplies are placed (bedrooms and main living areas — not utility rooms and hallways), duct lengths and routing (long duct runs require larger diameter to maintain airflow; undersized long runs reduce delivery to a fraction of design intent), and the balance between supply and exhaust (unbalanced systems create pressure differentials that force air through the envelope instead of through the unit).
This is where cheap ventilation design fails invisibly. A designer who draws the HRV in the mechanical room and calls it done has produced a document, not a design. The homeowner moves in, the system runs, and nobody notices that the master bedroom gets 15 CFM instead of the 30 CFM the design assumed — because there's no obvious symptom until someone wonders why they're always tired in the morning. Good ventilation design is fundamentally about the duct system, not the unit.
For homes using radiant or cold-climate heat pump systems without forced air distribution, the ventilation duct system operates independently and needs even more deliberate design — there are no heating ducts to piggyback on for air distribution. Our HRV/ERV design service produces a room-by-room duct layout for exactly this reason.
What good duct routing looks like
- Exhaust from bathrooms, kitchen, and utility room — not hallways
- Fresh air supply to all bedrooms and main living areas
- Duct lengths calculated — not assumed — to confirm airflow delivery
- Duct diameter sized for length to maintain TVC airflow
- Balanced system — supply and exhaust within 10% of each other
- Unit location that allows practical condensate drainage
- Service access maintained — not boxed in by finish work
- Summer bypass functionality if applicable
A complete MVDS for an Ontario building permit documents TVC calculation per CAN/CSA-F326, room-by-room supply and exhaust assignments, HRV/ERV selection with SRE at -25°C, and SB-12 compliance path. Our ventilation design service produces all of this — plus the duct layout that actually makes the system perform. See our HVAC permit requirements guide for where the MVDS fits into the overall permit package.
These requirements have been in force since January 1, 2025. They are not municipal options — they apply province-wide to all new Ontario residential construction. The most common deficiency is a permit package prepared to the old 2012 code that doesn't include the MVDS. Building departments are actively enforcing it.
Heat or Energy Recovery Required
OBC 2024 Section 9.32 requires mechanical ventilation with heat or energy recovery in every new home. An HRV or ERV is not optional — even for mild climate zones. The unit must be specified, and performance must be documented in the permit package.
MVDS — The New Form
A Mechanical Ventilation Design Summary must accompany every new home permit application. It documents TVC calculation per CAN/CSA-F326, supply and exhaust room assignments, SRE at -25°C, and the SB-12 energy compliance path. Missing MVDS = rejected application. See our HVAC permit requirements guide →
SRE Minimums at -25°C
The OBC specifies minimum Sensible Recovery Efficiency for HRVs at -25°C — not at the comfortable +0°C most manufacturers feature prominently. Zone 6 requires 60% SRE at -25°C for standard homes; higher-tier SB-12 paths require better. Specify equipment using the cold-condition ratings, not the headline numbers.
SB-12 Compliance Path
SB-12 is OBC's energy efficiency standard. The ventilation design must document which SB-12 compliance path the home uses and confirm the HRV/ERV meets the SRE or TER requirement for that path. A designer who doesn't know which path your home is on cannot produce a compliant MVDS. For the full OBC context, see the Ontario permit guide →
The ventilation system is one layer of the full mechanical package. It connects to the load calculation, the heating system, and the overall permit documentation in ways that matter for both performance and compliance.
Connected to the Load Calculation
Ventilation heat loss is a meaningful component of total building heat loss — particularly in tight homes. Our CSA F280 heat loss calculation accounts for ventilation load as part of the total heating demand. A load calculation that ignores ventilation heat loss underestimates total demand. A ventilation design that doesn't account for the load implications isn't fully coordinated.
Connected to the Mechanical Drawing Package
The MVDS is one document in a complete mechanical drawing package. It must be coordinated with the duct layout — supply and exhaust terminal locations shown on the floor plan, duct routing confirmed against structural elements, and equipment location documented for service access. A standalone MVDS without a coordinated floor plan is a compliance document, not a design.
Connected to the Heating System
In forced-air homes, the HRV typically integrates with the furnace duct system — the furnace fan distributes fresh air supply. In radiant or heat pump without forced air homes, the HRV ducts are fully independent. For ICF and high-performance homes, the optimal heating system for ICF in Ontario is a different conversation from a conventionally framed home, and the ventilation design strategy should reflect that.
Is an HRV or ERV actually mandatory in Ontario now?
Yes. OBC 2024 (in force since January 1, 2025) requires mechanical ventilation with heat or energy recovery in every new Ontario home. An HRV or ERV is no longer optional. The permit package must also include a Mechanical Ventilation Design Summary documenting the system. See our HVAC permit requirements guide for the full permit context, and our ventilation design service for how we produce the MVDS.
How do I choose between HRV and ERV for an Ontario home?
For the vast majority of Ontario Zone 6 and Zone 7 homes, an HRV is the right choice. Ontario's cold, dry winters and humid summers mean you generally want to exhaust interior moisture in winter and not import exterior humidity in summer — which is exactly what an HRV does. An ERV makes sense in very specific conditions: ultra-tight homes with very low occupancy where interior winter humidity drops uncomfortably low, or specialized applications with particular envelope and climate profiles. If you're not sure, ask — we can review your project and make a specific recommendation.
What is the MVDS and why does every Ontario permit application need it?
The Mechanical Ventilation Design Summary is a form documenting the ventilation system per CAN/CSA-F326 — Total Ventilation Capacity calculation, room-by-room supply and exhaust assignments, HRV or ERV selection with SRE or TER at -25°C, and SB-12 compliance path. It's been mandatory in every Ontario new home permit package since January 1, 2025 under OBC 2024. Applications submitted without it are returned as incomplete. Our ventilation design service produces this form as a standard deliverable.
What does SRE at -25°C mean and why does it matter?
Sensible Recovery Efficiency at -25°C is the heat recovery performance of an HRV under Ontario cold-weather operating conditions. Manufacturers typically feature their SRE at 0°C or +5°C on marketing materials — these numbers are meaningfully higher than cold-condition performance. OBC 2024 and SB-12 specify SRE minimums at -25°C. An HRV that meets 75% SRE at 0°C may deliver 55–60% at -25°C. The permit documentation and equipment selection must use the cold-condition rating.
Does the HRV design change if I have radiant floor heating instead of a furnace?
Yes — significantly. In a forced-air home, the HRV typically integrates with the furnace duct system. In a radiant home, the HRV ducts are fully independent — you're designing a dedicated supply and exhaust duct network without any heating distribution to piggyback on. This generally requires more careful duct routing, careful location selection, and attention to ensuring fresh air actually reaches all bedrooms and living areas at the designed flow rates. Our ventilation design service handles both approaches.
Can I add the MVDS to an existing heat loss report prepared by another designer?
Yes. If you have a heat loss report from another BCIN-registered designer and only need the ventilation design layer added, we can produce the MVDS and duct layout as a standalone add-on — provided we can review the existing load calculation to confirm the design temperatures and room data are consistent with our ventilation design inputs. Contact us with the existing report and we'll confirm scope and pricing.
How does the ventilation design connect to the full permit package?
The MVDS is one document in a complete mechanical permit package. For a new custom home, that package typically also includes a CSA F280 heat loss report, a duct layout drawn over floor plans, an equipment schedule, and a Schedule 1 designer declaration. See our mechanical drawings Ontario guide for a full layer-by-layer breakdown, and our full HVAC design service for the complete package.
What makes ventilation design in an ICF home different from a framed home?
ICF homes are typically tighter than framed homes — lower natural infiltration means ventilation is doing more of the air exchange work. The mechanical ventilation system must be sized for a home that contributes very little incidental infiltration, which can affect TVC calculations and duct design. ICF's lower heat loss also means ventilation heat loss becomes a proportionally larger share of total load. For how heating system selection interacts with this in an ICF build, see best heating system for ICF homes in Ontario.
Upload your floor plans and heating system details. We'll produce the full MVDS per CAN/CSA-F326, room-by-room duct layout, HRV or ERV selection with -25°C SRE documentation, and SB-12 compliance path — stamped and ready for your Ontario building permit portal. Can be produced standalone or as part of the full HVAC design package.
- Total Ventilation Capacity calculation per CAN/CSA-F326
- Room-by-room supply and exhaust assignments
- HRV or ERV selection with -25°C SRE documentation
- SB-12 compliance path confirmed
- Duct layout drawn over your floor plans
- BCIN-stamped MVDS — permit-ready in 48 hours
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