Key takeaways
- A heat pump moves heat that already exists outdoors into your home in winter, and out of your home in summer.
- Because it moves heat instead of making it, it can deliver 2–4 units of heat for every unit of electricity it uses.
- The same outdoor unit replaces your air conditioner, so you get cooling included.
- Cold-climate models keep working well below −20 °C, which covers almost every Toronto winter day.
The big idea: moving heat, not making it
A furnace burns fuel to create heat. A heat pump works more like your fridge: it uses a refrigerant to soak up heat in one place and release it somewhere else. Even air at −15 °C still contains a lot of heat energy — a heat pump collects it and concentrates it.
Because it’s moving heat rather than creating it, a heat pump can deliver more energy than it consumes. That ratio is called the coefficient of performance (COP). A COP of 3 means 3 kWh of heat for every 1 kWh of electricity.
The refrigerant cycle in four steps
- 1AbsorbCold, low-pressure refrigerant flows through the outdoor coil. It’s colder than the outside air, so it absorbs heat and turns into a gas.
- 2CompressThe compressor squeezes that gas. Compressing it raises its temperature sharply — well above room temperature.
- 3ReleaseThe hot gas flows to the indoor coil. Your blower (or the indoor unit’s fan) pushes room air across it, and the heat moves into your home.
- 4ExpandThe refrigerant passes through an expansion valve, drops in pressure and temperature, and heads back outside to start again.
A reversing valve switches the direction of the refrigerant. Now the indoor coil absorbs heat from your home and the outdoor unit releases it — exactly what a central air conditioner does.
The parts you’ll actually see
Why “variable-speed” matters
Older units were either fully on or off. Modern cold-climate heat pumps use an inverter-driven, variable-speed compressor that ramps up and down to match what your home needs. That means steadier temperatures, quieter operation, better efficiency and far fewer on/off cycles.
- Runs longer at low speed instead of blasting and stopping
- Holds temperature within a degree or so
- Ramps up on very cold days to deliver more heat
- Less wear from constant starts and stops
Backup heat: what happens on the coldest days
As it gets colder outside, a heat pump can deliver less heat just as your home needs more. The point where the two meet is the balance point. Below it, a second heat source tops things up.
| Backup option | How it works | Good fit when |
|---|---|---|
| Electric heat strips | Resistance elements in the air handler switch on automatically. | You’re going fully electric and your panel has capacity. |
| Your existing gas furnace (hybrid) | The thermostat hands off to the furnace below a set outdoor temperature. | Your furnace is in good shape and you want the lowest-risk switch. |
| Existing boiler or baseboards | Ductless heads carry most of the load; the old system covers peaks. | You have radiators or baseboard heat today. |
Common questions
Does a heat pump work when it’s −20 °C?
Cold-climate models are designed to keep producing heat at −20 °C and below, at reduced output and efficiency. Your installer sizes the system and backup so your home stays comfortable on the coldest nights.
Is a heat pump the same as geothermal?
Geothermal (ground-source) heat pumps collect heat from the ground through buried loops. This site focuses on air-source heat pumps, which collect heat from outdoor air and cost far less to install.
Why does steam come off the outdoor unit in winter?
That’s the defrost cycle. Frost builds on the outdoor coil in cold, damp weather; the unit briefly reverses to melt it. It’s normal and usually lasts a few minutes.