Guides · 2026-08-14
Why a heat pump saves less than the brochure says
A heat pump with a seasonal COP of 2.4 delivers 2.4 units of heat for every unit of electricity. Divide your heating consumption by 2.4 and you get a 58% saving. That figure is repeated across dozens of calculators, and it is wrong for most Quebec homes.
Hydro-Québec's own guidance says a heat pump can save up to 35% of heating consumption. The gap between 58% and 35% is not marketing caution. It is a real physical constraint, and understanding it is the difference between a sound decision and a disappointed one.
The unit only heats what it can reach
A wall-mounted head heats the air in the space it serves. In an open-plan main floor that can be most of the living area. It is not, however, heating the closed bedroom at the end of the hall, the basement, or the bathroom with the door shut.
Those rooms keep their electric baseboards, and those baseboards keep converting electricity to heat at one to one. Whatever share of your heating load they carry is not being saved at all.
Below the balance point, the backup takes over
A cold-climate heat pump keeps producing heat far below freezing, but its capacity falls as the outdoor temperature drops. At some outdoor temperature — the balance point — it can no longer meet the heat loss of the space on its own, and resistive backup makes up the difference.
In Montreal that happens for a meaningful part of the heating season. It is why a seasonal average COP is always lower than the headline rating, which is measured under mild conditions.
The arithmetic, with nothing hidden
Split the heating load into the share the heat pump actually serves — call it the coverage — and the share that stays resistive.
Electricity used = heating load × ( coverage ÷ COP + (1 − coverage) )
At 60% coverage and a seasonal COP of 2.4: 0.60 ÷ 2.4 = 0.25, plus the 0.40 that stays on baseboards, gives 0.65. You use 65% of the electricity you used before, so you save 35%. That is Hydro-Québec's figure, arrived at from first principles.
Drop the second term — pretend the heat pump carries everything — and you get 42%, or 58% saved. That single omission is where the doubled claims come from.
What changes the coverage
Coverage is the number worth arguing about, because it is the one you can influence. An open plan with a single well-placed head does better than a compartmented layout. A multi-head system serving bedrooms as well as the living area does better again. A unit sized and sited badly does worse.
This is also why a contractor quoting one confident savings figure should be asked what coverage they assumed. If they cannot answer, the number is decoration.
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FAQ
Is 35% still worth it?
For most Quebec homes on Rate D, yes — but judge it against your own consumption rather than a percentage. On a 22,000 kWh home the saving is in the region of $330 to $600 a year at current second-tier prices, before any equipment cost. Run your own figure rather than accepting an average.
Would a multi-head system save more?
It raises coverage, which is the term that matters most, so yes in energy terms. Whether the extra capital cost is repaid depends on your quote and how many rooms are currently on baseboards.
Does the calculator include installation cost?
No. It is an operating-energy comparison only. Equipment, installation, financing and grants all sit outside it, because they depend on your home and on programs that change.