Ask around and you’ll hear two completely different stories about heat pumps. One neighbour put one in and can’t stop talking about how comfortable and cheap winter has been. Another had one installed, spent a cold snap wearing a jacket indoors, and now tells anyone who’ll listen that heat pumps are a gimmick.
They’re almost always both telling the truth. Same idea, same physics. What isn’t the same is the machine that got hung on the wall, the math behind the install, and the house it’s attached to. This is about what separates those two stories, so you end up living in the first one.
The short version: a cold-climate heat pump, sized properly for a reasonably tight house, can carry you through a real winter. A standard unit, sized by guesswork, in a drafty house, often can’t. Whether it also saves you money comes down to what you pay for electricity compared to what you heat with now.
Wait, how does it pull heat out of freezing air?
It sounds backwards. If it’s −15°C out, where’s the heat supposed to come from?
The trick is that cold is relative. Air at −15°C still has a lot of heat in it. It doesn’t run out until you get down around −273°C. A heat pump circulates refrigerant through the outdoor coil at a temperature even colder than the air, so heat drifts into the refrigerant on its own. Then the compressor squeezes that heat up to a temperature that’s useful and sends it inside.
If you’ve ever felt warm air blowing off the back of a fridge, you already know this trick. It’s just aimed at your living room instead of your kitchen.
The important part is that it moves heat rather than burning something to make it. That’s why it can deliver more heat than the electricity it uses. It’s also why how well it works depends so heavily on how cold the air is.
What the brochure doesn’t dwell on
On a mild fall day, a good heat pump gives you three or four units of heat for every unit of electricity. That’s where the “300% efficient” line comes from, and it’s real. It’s also a mild-weather number. As it gets colder, it slides:
| Outdoor temperature | Heat delivered per unit of electricity (good cold-climate unit, roughly) |
|---|---|
| 10°C (50°F) | 3 to 4 |
| −15°C (5°F) | about 2 |
| −25°C (−13°F) | about 1.5 |
Those are ballpark figures, so ask for the manufacturer’s data on the specific model. Even at the bottom of that table you’re still doing better than electric baseboard, which gives you one for one, and better than a gas furnace, which maxes out around 95% and can’t go above one. It’s a slide, not a cliff, but it’s a slide that shows up on your bills.
A standard heat pump, one that isn’t built for the cold, has a much harder time. Some lose about half their heating power by −15°C. That’s behind most of the horror stories.
Why some installs leave people cold
The spec sheet trap. Heat pump ratings are measured at 8°C (47°F). At that temperature almost every unit looks wonderful. Cold-climate models are built differently, with variable-speed compressors that keep working as the temperature drops, but on paper they can look nearly identical to a standard unit. So don’t trust the headline rating. Ask what it delivers at −15°C.
Sizing it off the old furnace. It sounds logical. The old furnace kept the house warm, so match it. The problem is that plenty of older furnaces were oversized to begin with, and a heat pump has to be sized for your coldest normal day, not your average one. Undersize it and it runs flat out through every cold snap while the house slowly loses ground. The proper way to do it is a room-by-room heat loss calculation, called a Manual J in the US and a CSA F280 in Canada. If someone quotes you by square footage alone, it’s worth asking how they got that number.
The morning it looks like it’s on fire. Sooner or later you’ll glance outside on a cold morning and see a cloud of steam pouring off the outdoor unit. It looks alarming. It’s almost always the defrost cycle: frost builds up on the outdoor coil, so the unit briefly runs in reverse to melt it off. Totally normal. It’s fair to ask your installer how your system keeps the house warm while that’s happening.
A leaky house. This one is unglamorous. If warm air is escaping through the attic and around the windows, no heating system can keep up without being oversized and expensive to run. Houses that get sealed and insulated first can often get a smaller, cheaper system. If you’re doing both, do the air sealing first.
Three questions to ask before you sign anything
What does electricity cost compared to what you heat with now? This matters more than the heat pump itself. Being three times as efficient doesn’t make it three times cheaper, because the energy it runs on may cost more per unit. If you’re on propane, oil, or electric baseboards, the math usually favours the heat pump. If you’re on reasonably priced natural gas, the gap can be small, or even flip the other way. Your own bills will tell you.
Is it genuinely a cold-climate unit? Don’t take the brochure’s word for it. Ask for the heating output and efficiency at 5°F (−15°C). A true cold-climate unit should hold at least 70% of its rated heat at that temperature, with a COP of 1.75 or better. If the person quoting you can’t produce those numbers, that tells you something.
What happens on the coldest nights? A lot of homes in cold areas run dual-fuel: the heat pump does the heavy lifting from spring through most of winter, and the gas furnace steps in when it’s truly brutal. The heat pump doesn’t have to win at −25°C. It has to win in the shoulder seasons, which is most of the year. No gas? A cold-climate unit with electric backup can still carry the whole winter.
So is it right for your house?
It tends to shake out in one of three ways. If electricity is cheap relative to your fuel, and you get a proper cold-climate unit that’s sized right, a heat pump will probably save you money. If you have gas at a decent price, dual-fuel is often the happy middle. And if your rates say gas is cheaper all winter, a heat pump can still make sense for comfort and air conditioning, as long as you’re not counting on savings.
Whichever way you lean, get three quotes and compare the cold-weather numbers, not just the price. The cheapest quote is often the one that was sized by guesswork.
Quick answers
Do heat pumps work at −25°C? Good cold-climate models keep producing heat, just at lower efficiency. Many homes keep backup heat for the coldest nights.
Will one save me money? It depends on your rates, your climate, and your house. It isn’t guaranteed.
Do I need a permit? Rules vary by municipality and province or state. Check your local bylaws and permit requirements yourself, and confirm your contractor’s licensing before work starts.
Want help working through it?
Before you take a single quote, grab the free one-page heat pump check. It’s the 30-second bill test, the three questions to ask any contractor, and the numbers a good quote should contain. It takes a minute to read, and it’s free. Put your email in at ProGradeHomeScience.com/heat-pump-checklist and it opens right away.
Disclosure: Some links on this site may be affiliate links. If you buy through one, Pro Grade Home Science may earn a commission at no extra cost to you. This is general education, not advice for your specific home. Have a licensed professional assess your property before making equipment decisions.
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