Definition — what each machine actually is
A central AC is a one-way refrigerant loop: it moves heat from inside your home to outside during cooling season. In heating season, the AC does nothing.
A heat pump is a reversing refrigerant loop: in summer it works exactly like a central AC. In winter it runs backwards, extracting heat from outdoor air and delivering it inside — down to roughly –15 °C to –25 °C for a modern cold-climate model.
So a heat pump replaces both machines at once. It is functionally 'a central AC that also does heating' — which is why the comparison isn't apples-to-apples.
When to use each — the GTA decision tree
If your furnace is in the middle of its life (say, 8-15 years old) and your AC is on its last legs, replacing the AC with a heat pump and keeping the furnace as backup (a hybrid or 'dual-fuel' setup) is often the cost-optimal choice in Ontario. You get the shoulder-season efficiency of a heat pump and the deep-winter reliability of gas.
If both the furnace and AC are old and failing, and your electrical panel has capacity, a full cold-climate heat pump can replace both — a common Greener Homes-era retrofit path.
If your gas rate is cheap, your electrical panel is maxed out, or you're staying in the home only a few years, a straight AC + high-efficiency furnace replacement is often still the right answer.
Failure modes — the 'heat pumps don't work in Canada' myth
The old-generation heat pumps (pre-2015) really did struggle below –10 °C — the compressor's rated capacity dropped fast in cold weather and electric-strip backup ran constantly, driving winter bills up. That is why the reputation stuck.
Modern cold-climate heat pumps use variable-speed inverter compressors and vapour-injection to hold rated capacity down to about –15 °C, with continued (reduced) capacity below that. In a Scarborough or Ajax winter, they run all season — but sizing and installer quality matter enormously.
Where hybrid-heat setups fail is usually the thermostat logic: if the switchover to the furnace happens too late (or too early), efficiency drops. A properly commissioned dual-fuel thermostat has the economic balance point programmed in, not left at the factory default.
Proof — what the numbers actually say
For cooling alone, a modern heat pump and a modern central AC of the same SEER2 rating deliver essentially the same summer comfort and cost — the compressor tech is nearly identical.
For heating, a cold-climate heat pump running above its balance point routinely delivers a COP of 2.5–3.5 in Ontario shoulder weather — meaning 2.5–3.5 kWh of heat delivered per kWh of electricity consumed. Below the balance point, the COP drops and backup takes over.
Whether that saves money depends on your electricity vs gas rate. In parts of the GTA served by cheaper natural gas, a hybrid dual-fuel system is often the lowest-total-cost path; in homes without gas service, the heat pump wins outright.
Action — how to run the comparison for your home
Ask for two quotes side by side: (1) high-efficiency furnace + central AC, and (2) cold-climate heat pump + existing or new backup furnace. Ask each installer to state the equipment's SEER2, HSPF2, and rated capacity at –15 °C. Then ask for a written estimate of annual energy cost using your actual utility rates.
That is the only apples-to-apples comparison. Beware anyone who won't put those numbers on paper — and beware anyone who promises a specific rebate amount without confirming today's program rules. Rebate landscapes in Ontario shift; verify current program status before signing.