How air-source heat pumps cope with Canadian winters

How does an air source heat pump work?

An outdoor coil carries refrigerant that is colder than the air around it, so heat flows into the refrigerant and turns it to vapour. A compressor raises the vapour’s temperature and pressure, and an indoor coil hands that heat to the house air or to water. The refrigerant then expands, cools and returns outside. Air is not "warm" at minus ten degrees, but it still holds heat that this cycle can collect. Our heat pump explainer walks through the cycle in more detail.

Two main forms exist. Air-to-air systems deliver warm air through ducts or wall units. Air-to-water systems heat water for radiators, fan coils or in-floor loops, and some also supply hot water, which suits low-temperature hydronic systems such as those described in low-temperature hydronic heating.

What happens to performance when it gets colder?

Two things fall together: the heat output and the energy efficiency of the heating system. At the same time the house loses heat faster, so demand rises just as supply drops. Manufacturers publish performance tables that show capacity and efficiency at several outdoor temperatures, and that table is the document to check, not the headline efficiency figure.

Cold climate models use features such as variable-speed compressors and enhanced refrigerant injection to hold more capacity at low temperatures. The guide to cold climate heat pumps and our explainer on what the cold climate rating means show which ratings to look for.

What is the balance point and when does backup heat run?

The balance point is the outdoor temperature at which the heat pump’s output just matches the house’s heat loss. Below it, something else must make up the difference: electric elements, a gas furnace or a boiler. A well-sized cold climate system may rarely need help, while a smaller unit in an uninsulated house will lean on backup often.

That is why a heat-loss calculation comes first, as set out in sizing for cold climate homes. For very cold regions, pairing the heat pump with a furnace is common, and dual-fuel systems explain how the two share the work.

What cold-weather issues should you expect?

Frost builds on the outdoor coil in cold, humid weather, so the unit runs a defrost cycle, briefly reversing to melt it. Steam, dripping water and a pause in heating are normal; see defrost cycles and noise for what to watch. Mount the unit above the snow line with clear space around it, and avoid placing it under a roof edge that drops snow and ice on the fan.

Check that the drain path cannot refreeze on a walkway, and brush away drifts after storms. These small habits protect the unit and keep output steady.

Is an air source heat pump better than ground source?

Air-source units cost less to install and need no drilling, but they work harder in the coldest weather. Ground-source units draw on steadier underground temperatures, see ground temperature by depth, but cost more to install. The comparison in air-source versus ground-source heat pumps sets out both.

Drake Landing took a third route. It stored summer solar heat in the ground and used it for winter heating in a district loop, rather than lifting heat from cold air (see borehole storage). That is a very different design, and it needed a large shared field, which a single house cannot copy.

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