How a Heat Pump Works in Winter — and the −25° Question

How can a heat pump pull heat out of cold air?

Even −20°C air contains heat energy — a heat pump doesn't create heat, it moves it. Refrigerant in the outdoor unit absorbs heat from the outside air, a compressor concentrates it, and the indoor unit releases it into your ducts. Because it's moving heat rather than making it, a heat pump delivers roughly two to three units of heat for every unit of electricity it uses through most of the season. That's the entire economics of the switch.

So, will it heat my house at −25°C?

A modern cold-climate heat pump is rated to keep heating at −25°C to −30°C — that's the equipment class the rebate programs require, and it's a different machine from the heat pumps that earned a bad reputation in the 1990s. What changes in deep cold is efficiency, not function: the colder it gets, the harder the unit works for each unit of heat. That's why your system includes backup heat — below the balance point, the backup takes over automatically and the house stays warm the same way it always has.

What about defrost cycles and snow?

In freezing, humid weather, frost builds on the outdoor coil and the unit briefly reverses to melt it — a defrost cycle. You'll hear it; it lasts a few minutes and it's normal. Installers mount the unit raised off the ground, out of the drift line, with clearance so meltwater drains away. A properly placed unit in an Ontario winter is a solved problem — there are hundreds of thousands of them running in colder climates than ours, from Quebec to Scandinavia.

What's the honest catch?

Sizing and installation quality matter more here than brand. An undersized unit leans on expensive backup heat; an oversized one cycles and wears. That's why the rebate process starts with an in-home visit and a proper heat-loss look at your house — and why the cheapest quote is rarely the cheapest winter.