Last updated: By HeatPumpIndex Evidence Desk
Two published temperatures settle most of this argument: the one your region is sized against, and the one on the box. Pick both and the checker tells you whether the machine is still running when the building code says it is coldest, and what the backup would have to carry if it is not.
The temperature in brackets is what a heat loss calculation sizes for in that region, as published by Ontario Heat Loss. It is not the coldest night on record.
Only the floors you heat. This sets the load the backup would have to carry.
The verdict
Still running at -18 °C, with 7 degrees to spare
A unit that stops at -25 °C is still operating when Toronto and the GTA is at its -18 °C design temperature. Whether it still has enough output at that point is a different question, and it is the one your installer answers from the model’s capacity table.
What the backup would have to carry, worst case
18,000 to 23,500 BTU/h
As electric resistance heat that is 5.3 to 6.9 kW, drawing 22 to 29 amps at 240 volts. That is the number that decides whether your panel needs upgrading.
Your backup is already there
Keeping the furnace makes this a dual fuel system. The heat pump takes the mild majority of the season, a control hands the house over below a set outdoor temperature, and the panel upgrade the amperage above would otherwise force is usually avoided entirely.
The load is Ontario Heat Loss’s published -18 °C figure for a 2,000 sq ft house in Toronto and the GTA, scaled to the area you entered. It is a sanity check on a quote, not the CSA F280 calculation the building code requires.
NRCan separates three outdoor temperatures that homeowners routinely hear as one thing, and the difference between them is where cold climate installations succeed or fail. Each is quoted below in NRCan’s own words rather than paraphrased, because the wording is the point.
Only the third is printed on a spec sheet, and it is the one this checker compares against your design temperature. The first is calculated per house from the model’s capacity table and your heat loss, and it is always warmer than the cut-off. The second moves with energy prices and is the reason a dual fuel control has a setting at all.
Below the cut-off temperature, the heat pump contributes nothing and the backup carries the whole design heat loss. In a house with no gas that backup is electric resistance heat, and resistance heat is honest about its physics: one kilowatt hour in, one kilowatt hour of heat out, no multiplier. Converting the design load at 3,412 BTU per hour per kilowatt and dividing by the 240 volt circuit Imperial Heating says a heat pump needs gives a current in the twenties to the low thirties of amps for an ordinary GTA house, before the rest of the house is counted.
That is why the electrical panel, not the heat pump, is so often the item that decides the quote. A 100 amp service already carrying a range, a dryer and an EV charger may have nowhere to put thirty more. The answer is either a service upgrade, a load management device, or keeping the furnace and never needing the strips in the first place.
Choosing a colder-rated machine attacks the same problem from the other end. Every degree of headroom between the rating and the design temperature is a set of hours the backup does not have to cover, which is the real argument for paying more for a unit rated to -30 rather than -15.
It will not model how much output your unit still has at minus 20. That figure lives in each model’s own capacity table, varies across the market by a factor of two, and nobody publishes a general curve for it. Producing one here would mean inventing a number and dressing it as research, which is the failure this whole set of calculators is built to avoid.
It will not replace a heat loss calculation either. The load it prints is Ontario Heat Loss’s published figure for a 2,000 square foot house in your region, scaled to the area you typed. Ontario Building Code 9.33.2.2 requires the real number to come from a CSA F280 calculation stamped by a BCIN holder, which reads insulation, window area, air tightness and orientation. A web form knows none of those.
What it does is put two published temperatures beside each other, which is enough to tell you whether the conversation you are about to have with an installer is about fine tuning a balance point or about how the house gets through January.
Four of the 4 design temperatures, the operating range, the efficiency figures and the circuit voltage all come from the pages below, read during this build rather than recalled.
The one question worth insisting on is the first of NRCan’s three: at what outdoor temperature does this specific model, at this capacity, stop carrying this house. An installer who can answer that has done the work. HeatPumpIndex lists 221 heat pump installers across the Greater Toronto Area, and the three below rank highest on our HeatPumpIndex score.
In its own words, from its website: Experience top-notch HVAC repair and maintenance services in Milton and Oakville ON with Free Air Heating & Air Conditioning Ltd. Trust our expert team for AC, furnace, ductless mini-split, heat pump services, and more. Schedule your service today!
Carried on this directory for ductless mini split work and heat pump installation from a base in Leaside. Their own website names heat pump work, and the company appears on Ontario's Home Renovation Savings register.
In its own words, from its website: Family-owned for 75+ years. Service, repairs, installations & honest pricing.