OBC 2024 HRV Requirement Toronto Explained: What Changed and Who Is Affected

# OBC 2024 HRV Requirement Toronto Explained

Ontario Building Code 2024 took effect on January 1, 2024 and quietly tightened the mechanical ventilation rules across the province. Most Toronto homeowners only learn about it when their renovation permit is rejected or when their post-renovation blower-door test triggers an unexpected requirement. This guide walks through what actually changed, who is affected, and how the permit reviewer evaluates an HRV/ERV submission. For the pillar context, see [HRV & ERV Installation Toronto: The Complete 2026 Guide](/blog/hrv-erv-installation-toronto-2026-complete-guide).

What Changed in OBC 2024

Three substantive shifts:

1. Balanced Mechanical Ventilation Mandatory in New Construction

Under the previous code, exhaust-only ventilation (a kitchen range hood plus bath fans plus a fresh-air intake to the furnace return) was acceptable for many new homes. OBC 2024 requires balanced mechanical ventilation with heat or energy recovery as the principal ventilation system. In practice, this means an HRV or an ERV.

2. Retrofit Trigger at 1.5 ACH50

OBC 2024 sets a measured envelope tightness threshold. Where post-renovation blower-door testing measures the home at 1.5 ACH50 or tighter, mechanical ventilation that meets CSA F326 is required. Practically, any deep retrofit that includes:

• attic spray foam to R-50 or higher,
• comprehensive air-sealing,
• new triple-pane windows replacing original single-pane, or
• exterior continuous-insulation re-cladding

will hit the 1.5 ACH50 threshold and trigger the requirement.

3. Mechanical Ventilation Design Summary (MVDS)

Permit reviewers expect a one-page MVDS that documents:

• Principal ventilation rate per CSA F326.
• Exhaust ventilation rate.
• Balanced supply rate (within 10 percent of exhaust).
• Equipment selected with sensible recovery efficiency.
• Duct sizing and routing.
• Exterior hood locations with required separations.

Without an MVDS, the permit is held until one is submitted.

CSA F326-M91 in One Page

CSA F326 is the Canadian standard for residential mechanical ventilation, dating to 1991 and refreshed in 2018. It sets:

• Principal ventilation rate: 5 L/s (about 10 CFM) per primary bedroom plus 5 L/s for each additional bedroom plus 5 L/s for each habitable room beyond.
• Maximum imbalance: 10 percent between supply and exhaust.
• Filtration: minimum MERV 8 on supply.
• Commissioning: balanced flow report at install.

OBC 2024 references CSA F326 directly. A unit and install that meets F326 satisfies OBC.

For the technical math, see [HRV Energy Recovery Efficiency Explained](/blog/hrv-energy-recovery-efficiency-explained).

Who Is Affected

New Home Buyers

Anyone closing on a new build under permit pulled in 2024 or later receives an HRV or ERV as standard, plus an MVDS in the closing package. Verify the unit and the MVDS at walk-through.

Major Renovators

Any renovation that includes attic spray foam, exterior insulation, full window replacement, or comprehensive air-sealing should plan for HRV/ERV inclusion in the scope. The blower-door test that wraps a deep retrofit will determine whether the requirement formally applies.

Smaller Renovators

A single-room renovation, a kitchen refresh, or a bathroom rebuild will not typically trigger the requirement on its own. The home as a whole has to cross 1.5 ACH50.

Condo Buyers and Owners

Most new Toronto condos under OBC 2024 ship with an in-suite HRV or ERV as part of base spec. Older buildings (pre-2024) may rely on corridor pressurization and bath exhaust only — no in-suite recovery. Retrofits in older condos require board approval. See [HRV Condo Installation Toronto](/blog/hrv-condo-installation-toronto-low-rise).

What Permit Reviewers Want

A typical Toronto Building permit review on an HRV/ERV submission checks:

• MVDS attached, signed, dated.
• HRV/ERV equipment specified by make, model, AHRI or HVI listed sensible recovery efficiency.
• Duct sizing per CSA F326 (5 or 6 inch insulated typical).
• Exterior hood locations with 6-foot minimum separation between intake and exhaust, plus separation from gas furnace flue, dryer exhaust, and fireplace flue.
• Drainage path for condensate (insulated drain to floor drain or condensate pump).
• Boost switches in bathrooms or full-time auto-boost via humidity sensor.
• Filter spec MERV 8 minimum on supply.

A complete submission typically clears in 5-15 business days. Incomplete submissions add 2-4 weeks.

What Permit Reviewers Reject

Common rejections we see:

• Exhaust-only ventilation specified on a new home.
• HRV unit listed but no MVDS attached.
• Intake hood within 6 feet of exhaust hood (re-entrainment risk).
• Intake hood within 10 feet of dryer exhaust.
• 4-inch ductwork on a 100+ CFM unit (will not meet CFM at acceptable static pressure).
• No commissioning balancing report planned.
• Unit located in unconditioned attic without freeze protection.

How RenoHouse Handles the Permit

We coordinate the MVDS through our HVAC-licensed installer subcontractor (some carry an in-house ventilation designer; others partner with TSSA-registered subs for the design). The MVDS is prepared after the load calculation and before permit submission. Our coordinator handles:

• Pre-permit MVDS draft and sign-off.
• Permit submission with the broader retrofit scope.
• Pre-construction blower-door test (where part of the scope).
• Post-construction balancing test and commissioning report.
• Submission of the closeout package to the city and to Enbridge HER+ for rebate.

Penalties for Non-Compliance

OBC enforcement on residential ventilation is permit-driven, not patrol-driven. The risk surfaces at:

• Permit final inspection. Without an HRV/ERV where one is required, the inspector withholds occupancy.
• Resale. Real-estate lawyers and home inspectors increasingly check for code-compliant ventilation on post-2024 renovated homes.
• Insurance. Some insurers ask about ventilation on a major-renovation policy refresh.

The fix is straightforward: meet the requirement at install time. Retrofitting an HRV after the home is finished and the blower-door test has triggered the rule is meaningfully more expensive than including it in the original scope.

Practical Decisions for Toronto Homeowners in 2026

If you are doing a renovation that will tighten the envelope below 2.0 ACH50, plan for an HRV/ERV in the scope. The marginal cost of including it during the renovation is typically $3,000-$5,500. The cost of retrofitting after-the-fact, once finished surfaces are in place, is typically $5,500-$9,000.

If you are a new-build buyer, verify the unit and the MVDS at handover.

If you are a small-renovation homeowner, no immediate action is required, but consider the IAQ benefit on its own merits.

How OBC 2024 Connects to Federal Rebates

The same homes that fall under the OBC 2024 ventilation requirement typically also qualify for:

• Greener Homes Loan up to $40K interest-free (HRV/ERV bundled with envelope or heat pump).
• Enbridge HER+ up to $1,500 for HRV/ERV plus pre/post audits.
• Ontario HRSP up to $10,000 total bundle cap.

For the rebate walkthrough, see [HRV Greener Homes Rebate Toronto](/blog/hrv-rebate-greener-homes-toronto).

Final Word

OBC 2024 is not punitive. It catches up to a building science reality: tighter homes need balanced mechanical ventilation. Toronto's housing stock is tightening every year under air-sealing and insulation programs, and the OBC mandate ensures the indoor air keeps up. RenoHouse coordinates the MVDS, permit, install, and commissioning with HVAC-licensed installers and TSSA-registered design subs.

Book at [/services/hvac-energy/hrv-erv-installation](/services/hvac-energy/hrv-erv-installation). For deeper reads, see [HRV & ERV Installation Toronto: The Complete 2026 Guide](/blog/hrv-erv-installation-toronto-2026-complete-guide), [HRV vs ERV Toronto: Which to Choose](/blog/hrv-vs-erv-toronto-which-to-choose), [HRV Ductwork Design Toronto Renovation](/blog/hrv-ductwork-design-toronto-renovation). Related: [HVAC Thermal Audit (FLIR)](/services/inspections-diagnostics/hvac-thermal-audit).