Ontario BTU Calculator
Detailed heating and cooling load estimate sized for Ontario’s cold winters and warm summers. Pre-set to Zone 6 (cold) as a practical Ontario baseline — adjust for southern Ontario vs northern Ontario below. Most Ontario homes need 30–50 BTU per sq ft for heating and 14–22 BTU per sq ft for cooling.
Updated for 2026 Ontario building codes and energy rebate programs.
On this page: Calculator · Ontario climate zones · Ontario HVAC tips · Rebates · TOU rates & HRV · Equipment guide · Unit conversions · FAQ
Just need a quick estimate? The simple BTU calculator gives you an answer in 10 seconds. For the full US-default version, see the advanced BTU calculator. For all Canadian provinces, see the Canada BTU calculator.
Ontario rule of thumb
Heating in Ontario often lands around 30–50 BTUs per square foot depending on insulation, air sealing, ceiling height, and how cold your region gets. Cooling loads are usually lower (often 14–22 BTUs per square foot), but humidity, sun exposure, and upper floors can push the number higher.
This calculator is pre-configured for Ontario (Zone 6 baseline) with Canadian insulation standards. Results are in BTUs with watt equivalents for heating loads. For a code-compliant load calculation, consult an HVAC contractor or use an ACCA Manual J / CSA F280 tool. You can also get a free HVAC quote from local Ontario contractors.
Ontario climate zones (quick guide)
Ontario spans a wide range of winter design temperatures. Most of southern Ontario maps to Zone 6 (cold), while northern Ontario is closer to Zone 7 (very cold). If you’re unsure, choose the colder zone for safer winter heating sizing.
| Ontario area | Example cities | Zone | Heating note | Multiplier |
|---|---|---|---|---|
| Southwestern Ontario | Windsor, London | 5–6 | Milder winters; drafts still matter | ×1.05–1.10 |
| Golden Horseshoe | Toronto, Hamilton, Niagara | 6 | Cold winters; wind + leakage drive BTUs | ×1.10 |
| Eastern Ontario | Ottawa, Kingston | 6 | Colder nights; pay attention to insulation | ×1.10–1.15 |
| Northern Ontario | Sudbury, Thunder Bay, Timmins | 7 | Very cold winters; higher heating demand | ×1.20 |
For winter design temperatures by city, check Environment Canada’s climate data.
Ontario HVAC sizing tips
Air sealing beats extra BTUs
In Ontario winters, drafts can dominate comfort. Weatherstripping and sealing attic bypasses often reduce heating demand more than upgrading equipment size. A thermal leak detector ($30–50) makes finding leaks easy when it’s cold outside.
Attic insulation is huge
Heat loss through the ceiling is a common Ontario problem. Upgrading attic insulation to R-50+ and sealing around recessed lights and hatches can lower required BTUs and make rooms feel more even. Ontario’s SB-12 standard calls for R-50 to R-60 attic insulation in new construction.
Basements: warmer vs drier
Ontario basements typically need more heating than you’d expect due to below-grade walls, and they can be damp in summer. A hygrometer ($10–15) tracks humidity, and a dedicated dehumidifier can improve comfort without changing AC size.
Cooling is still real
Southern Ontario summers can be humid, with temperatures regularly exceeding 30°C. Avoid oversizing AC so it runs long enough to dehumidify. The window AC calculator and mini split calculator can help size cooling equipment.
Heat pumps in Ontario
Cold-climate heat pumps rated for −25°C to −30°C are now practical for most of southern Ontario (Zone 6) as primary heat. In northern Ontario (Zone 7), they’re typically paired with a gas furnace backup. The Canada Greener Homes Initiative and Ontario provincial rebates can offset installation costs. Size one with the heat pump calculator.
Low-cost Ontario comfort upgrades
Weatherstripping ($5–15) reduces drafts at doors and windows. Door sweeps ($8–20) seal gaps under exterior doors. Window insulation kits ($10–30) reduce cold-window discomfort. Spray foam ($10–40) seals rim joists and attic penetrations. Outlet gaskets ($5–10) stop infiltration on exterior walls.
For basements: hygrometer ($10–15) and dehumidifier ($150–350). A smart thermostat ($25–250) can cut heating costs 10–15% — ecobee (Canadian company), Google Nest, or Honeywell Home. An energy monitor ($20–30) can verify savings. The energy cost calculator estimates annual costs.
Ontario energy rebates for heating & cooling upgrades
Ontario has some of the most accessible rebate stacking in Canada. Most programs can be combined, and the Enbridge program is available to nearly every Ontario gas customer.
Enbridge Home Efficiency Rebate Plus (HER+)
The Enbridge Home Efficiency Rebate+ program offers up to $5,000 for eligible home energy upgrades including: air-source heat pump installation (up to $5,000), insulation improvements (up to $3,000), air sealing (up to $1,000), and smart thermostat installation ($75 rebate). Available to Enbridge Gas residential customers. A pre-retrofit home energy assessment is required. This program stacks directly with the federal Canada Greener Homes grant.
Canada Greener Homes (Ontario)
The federal Canada Greener Homes Initiative adds up to $5,000 in grants on top of Enbridge rebates. Combined, an Ontario homeowner installing a cold-climate heat pump with insulation upgrades can access up to $10,000 in combined rebates. An EnerGuide home evaluation is required for both programs — many Ontario energy auditors offer bundled assessments that satisfy both requirements in one visit.
Ontario Electricity Support Program (OESP)
Lower-income Ontario households may qualify for the Ontario Electricity Support Program, which provides monthly bill credits of $35–$113 depending on household size and income. If you’re replacing gas heat with electric or a heat pump, confirming OESP eligibility before switching can meaningfully change the economics.
| Program | Max rebate | Key requirement | Stackable? |
|---|---|---|---|
| Enbridge HER+ (heat pump) | $5,000 | Enbridge Gas customer; pre-assessment | ✅ Yes — stacks with federal |
| Canada Greener Homes Grant | $5,000 | EnerGuide evaluation | ✅ Yes — stacks with Enbridge |
| Enbridge HER+ (insulation) | $3,000 | Enbridge Gas customer; pre-assessment | ✅ Yes — stacks with above |
| Enbridge HER+ (smart thermostat) | $75 | Approved models only | ✅ Yes |
| Canada Greener Homes Loan | $40,000 (0%) | Interest-free; same EnerGuide assessment | ✅ Yes — stacks with grants |
Rebate amounts and eligibility change. Always confirm current amounts directly with each program before purchasing equipment. Correct BTU sizing matters for rebate eligibility — most programs require equipment to be appropriately sized.
Ontario electricity rates and time-of-use pricing
Most Ontario electricity customers are on time-of-use (TOU) pricing set by the Ontario Energy Board. This means the cost of running an electric heater, heat pump, or AC varies significantly by time of day.
How TOU affects BTU sizing decisions
Ontario’s TOU rates have three tiers: off-peak (typically overnight and weekends), mid-peak, and on-peak (weekday afternoons and evenings). On-peak rates can be 2–3× the off-peak rate in summer. This means:
- A correctly sized heat pump that runs steadily during off-peak hours costs significantly less than an oversized unit that blasts on-peak.
- Pre-cooling or pre-heating during off-peak hours with a smart thermostat can reduce on-peak runtime substantially.
- Electric baseboard heating (which has no TOU optimization capability) costs more to run in Ontario than heat pumps that can be programmed around TOU windows.
HRV requirements under the Ontario Building Code
The Ontario Building Code (OBC) requires heat recovery ventilation in new residential construction. Specifically, OBC Section 9.32 mandates that principal air-handling systems in new homes include heat recovery ventilation when the home has a certain level of airtightness. This is why virtually all new Ontario homes include an HRV (heat recovery ventilator).
For Ontario homeowners undertaking major renovations or building new, the HRV must be sized to meet the ASHRAE 62.2 ventilation rate procedure. Use the HRV & ERV sizing calculator to determine the required CFM based on your floor area and number of bedrooms. In Ontario’s climate, HRVs are strongly preferred over ERVs — the cold, dry winter air means you want heat recovery without moisture transfer.
Not sure whether your Ontario home has an HRV? Look for a white or grey box on your furnace room wall with two duct connections — one for exhaust, one for fresh air supply. If yours is undersized or you’re adding square footage, the HRV sizing calculator can confirm your required CFM.
Equipment sizing guide for Ontario homes
Ontario heating needs are often higher than many US regions due to colder design temperatures. Here’s how BTU results map to equipment:
Heating equipment
| BTU range | Equipment type | Ontario context |
|---|---|---|
| Up to 5,200 | 1,500W space heater | Supplemental heat for small rooms, offices |
| 5,200–18,000 | Infrared heater, mini split, or baseboard | Single-room heating, basement bedrooms, garages |
| 18,000–60,000 | Cold-climate mini split or small furnace | Large rooms, small homes, condos, additions |
| 60,000–100,000 | Gas furnace (high-efficiency, 96%+ AFUE) | Typical southern Ontario home |
| 100,000–120,000+ | Gas furnace or dual-fuel (furnace + heat pump) | Larger homes, northern Ontario |
Heating-specific calculators: Furnace size · Heat pump · Space heater
Cooling equipment
Air conditioning has become increasingly common across southern Ontario, where summer temperatures regularly exceed 30°C and humidity can make upper floors uncomfortable.
| BTU range | Equipment type | Ontario context |
|---|---|---|
| 5,000–8,000 | Window AC or portable AC | Bedrooms, home offices, condo bedrooms |
| 8,000–14,000 | Portable AC or mini split | Living rooms, open-concept condos |
| 14,000–36,000 | Mini split or central AC | Whole-condo, main floor + upstairs |
Cooling-specific calculators: Window AC · Portable AC · Mini split · AC size. All equipment: equipment by BTU range.
Frequently asked questions
How many BTUs do I need to heat a home in Ontario?
A common Ontario heating range is about 30–50 BTUs per square foot, depending on insulation, air sealing, ceiling height, and how cold your region gets. Older, draftier homes and northern Ontario typically need the higher end. Use the calculator above for a room-by-room estimate.
What climate zone should I pick for Ontario?
Most of southern Ontario is a good match for Zone 6 (cold). Northern Ontario is often closer to Zone 7 (very cold). If you’re unsure, choose the colder zone for safer winter sizing. See the Ontario zone guide above.
How many BTUs do I need for AC in Ontario?
Cooling loads in Ontario are often around 14–22 BTUs per square foot. Humidity, sun exposure, lots of windows, and top-floor rooms can push the result higher. For comfort, avoid oversizing if humidity control matters.
Should I oversize my furnace or air conditioner?
Usually no. Oversizing can cause short-cycling and uneven temperatures, and oversizing AC can reduce dehumidification. It’s better to size correctly and improve air sealing, attic insulation, and duct sealing. For whole-home sizing, confirm with an ACCA Manual J / CSA F280 calculation. You can also get a free HVAC quote.
Are heat pumps practical in Ontario?
Cold-climate heat pumps rated for −25°C to −30°C are now practical in southern Ontario (Zone 6) as primary heat. In northern Ontario (Zone 7), they’re typically paired with a gas furnace backup. The Canada Greener Homes Initiative and Ontario provincial rebates can offset installation costs. Size one with the heat pump calculator.
How do I convert between BTUs and kilowatts?
1 kW = 3,412 BTU/hr. For example, 10 kW is about 34,120 BTU/hr. For electric baseboard sizing, divide your heating BTU result by 3,412 to get kW. See the conversion table below.
What’s the difference between this and the Canada calculator?
Both use the same math. This page is focused specifically on Ontario — with Ontario city examples in the zone table, SB-12 insulation references, and Ontario-specific tips for basements, humidity, and air sealing. For all Canadian provinces, see the Canada BTU calculator.
What rebates are available for heat pumps in Ontario?
Ontario homeowners can stack two major programs: the Enbridge Home Efficiency Rebate+ (up to $5,000 for Enbridge Gas customers) and the federal Canada Greener Homes Grant (up to $5,000). Combined, eligible Ontario homeowners can access up to $10,000 in grants. See the full Ontario rebates table above.
Do new Ontario homes require an HRV?
Yes. The Ontario Building Code (OBC Section 9.32) requires heat recovery ventilation in new residential construction. HRVs are strongly preferred over ERVs in Ontario’s cold, dry winters. Use the HRV & ERV sizing calculator to determine required CFM for your floor area and bedrooms. See the HRV requirements section above for details.
Quick unit conversions
Ontario HVAC uses a mix of imperial and metric. These conversions are useful when comparing equipment and calculating loads:
| From | To | Multiply by |
|---|---|---|
| Metres | Feet | 3.281 |
| Square metres | Square feet | 10.764 |
| BTU/hr | Kilowatts | 0.000293 |
| Kilowatts | BTU/hr | 3,412 |
| Tons (cooling) | BTU/hr | 12,000 |
| °C | °F | (°C × 1.8) + 32 |
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