Worked Quotes and Choosing a System
Heat pump sizing in Canada: heat loss calculations and a bill-based sanity check
How contractors should size a heat pump or furnace for a Canadian home using a CSA F280 heat loss calculation, plus a worked check using your gas or oil consumption.
A heat pump should be sized from your home's heat loss at your local design temperature, calculated room by room, and then matched to equipment by its capacity at that temperature, not by the size of the old furnace. In Canada the standard method is CSA F280, which accounts for walls, windows, ceilings, basement, air leakage and ventilation. You can sanity-check any contractor's figure with your own fuel bills, using the arithmetic below. Getting the size right matters more for heat pumps than for furnaces: too small and the backup heat runs too often; too large and the unit short-cycles in mild weather, losing efficiency and comfort.
This guide is part of how to compare HVAC quotes.
What a proper heat loss calculation includes
| Input | Where it comes from | Why it matters |
|---|---|---|
| Design temperature | National Building Code climatic data for your location | Sets the coldest condition the system must meet |
| Indoor temperature | Usually around 21–22 °C | The temperature difference drives the heat loss |
| Wall, ceiling, floor areas and insulation | Measurements and inspection | Conduction losses |
| Windows and doors | Size, glazing type | Often the weakest part of the envelope |
| Air leakage | Blower door test (from an EnerGuide evaluation) or estimate | Can be a large share of the load in older homes |
| Ventilation | HRV/ERV or exhaust fans | Fresh air must be heated |
| Basement and slab | Below-grade walls, floors | Significant in Canadian homes |
The output is heat loss in BTU/h (or kW) for each room and for the whole house. Room-level results also show whether ducts or ductless heads can deliver heat where it is needed. If you had an EnerGuide home evaluation for a past program, its air leakage test and house model are useful inputs; ask the contractor to use them.
Design temperatures across Canada
The National Building Code lists January design temperatures for hundreds of locations. They range roughly from about −7 °C in Vancouver to colder than −30 °C in Winnipeg and much of the Prairies, with southern Ontario and southern Quebec in between. Provincial building codes use the same type of table. Ask which design temperature was used and check it against the code value for your municipality; a contractor using a milder temperature than the code will undersize.
Bill-based sanity check: worked example
This method uses last winter's fuel use to estimate the house's heat loss rate. It is a check, not a replacement for a calculation. Illustrative figures for a gas-heated home near Toronto.
- Annual gas use for heating. Your bill shows 2,300 m³ a year. Estimate summer use (water heater, dryer, stove) from your July and August bills: say 50 m³ a month, so 600 m³ a year. Heating gas ≈ 2,300 − 600 = 1,700 m³.
- Convert to heat delivered. Natural gas has roughly 10.3 kWh of energy per m³ (check the heat value on your utility's information; it varies slightly). With a furnace of 95% efficiency: 1,700 × 10.3 × 0.95 ≈ 16,635 kWh of heat a year.
- Divide by heating degree days. Suppose your area has about 3,800 heating degree days (below 18 °C) a year. Heat loss per degree-day = 16,635 ÷ 3,800 ≈ 4.38 kWh per °C-day, or 4.38 ÷ 24 ≈ 0.18 kW per °C.
- Scale to design conditions. Indoor 21 °C, design −18 °C: difference 39 °C. Heat loss ≈ 0.18 × 39 ≈ 7.1 kW, or 7.1 × 3,412 ≈ 24,200 BTU/h, about 2 tons.
If a contractor proposes a 100,000 BTU/h furnace or a 5-ton heat pump for this house, ask why. Heating degree-day data for Canadian locations is published by Environment and Climate Change Canada; internal heat from people and appliances means this method tends to underestimate slightly, so treat the result as a floor.
From heat loss to equipment
| Choice | Sizing approach |
|---|---|
| Cold-climate variable-speed heat pump, full electric | Match capacity at design temperature as closely as practical; size backup strips for any remaining gap and for emergencies |
| Heat pump with gas furnace backup (hybrid) | Size the heat pump to the cooling load or slightly above; the furnace covers the coldest hours |
| Ductless heads | Size per room or zone from the room-by-room results |
| Gas furnace | Output near the heat loss with modest margin; avoid large oversizing |
| Ground-source | Loop and unit sized to the heat loss; undersized loops lose efficiency over years |
Then use the capacity in tons (heat loss ÷ 12,000) in the heating system cost estimator.
Cooling load and balance
Heat pumps also cool. In most of Canada the heating load is larger than the cooling load, so a unit sized for heating can be oversized for cooling, which reduces dehumidification in summer. Variable-speed units narrow this problem by running at low output. Ask the contractor for both the heating and cooling loads.
Improve the envelope before you size?
Air sealing and insulation reduce the heat loss and therefore the size and cost of the heat pump. If you plan envelope work within a year or two, ask for the calculation to be done on the improved house, or choose a variable-speed unit that can turn down.
Mistakes to avoid
- "Same size as the old one." Old furnaces were often oversized.
- Using nominal tons instead of capacity at design temperature. See cold-climate price factors.
- Ignoring the basement. Finished basements are part of the load.
- Forgetting ducts. Airflow needs to match the new equipment. See ducted versus ductless.
- Skipping a written report. Ask for the calculation summary as part of the quote.
For what the right size means for your bills, see the running-cost comparison.
FAQ
Can I calculate heat loss myself?
You can do the bill-based check above. A full CSA F280 calculation needs measurements and software; energy advisors and trained HVAC designers do them.
What if I heat with oil or propane?
Use litres instead of m³: heating oil has roughly 10.6 kWh per litre and propane roughly 7.0 kWh per litre, multiplied by your appliance efficiency.
Does an EnerGuide evaluation give the heat loss?
It models the house's energy use and measures air leakage, which a designer can use. It is not the same as a room-by-room design calculation.
Sources
- CSA Group — CSA F280 residential heat loss and heat gain
- National Research Council Canada — National Building Code climatic design data
- Environment and Climate Change Canada — climate normals and degree-day data
- Natural Resources Canada — EnerGuide home evaluations and heat pump guides
- HRAI — residential heat loss and duct design training
