More than half the "my heat pump isn't heating" calls we take turn out to be a heat pump working exactly as designed. That isn't a criticism of the homeowner — it's a consequence of the fact that a heat pump heats a house in a genuinely different way from a furnace, and nobody explains that at handover.
The rest are real faults, and they're worth catching early because a heat pump that's underperforming quietly is usually leaning on expensive backup heat to cover for it.
Here's how to tell which one you have.
The air is meant to feel cooler than a furnace
This is the single biggest source of confusion, so it's worth being precise about.
A gas furnace delivers air at roughly 49 to 60°C. Put your hand over the register and it feels hot, because it is hot — well above body temperature.
A heat pump delivers air at roughly 32 to 43°C. Body temperature is about 37°C. So the air coming out of your register can be genuinely warming the house while feeling neutral, or even slightly cool, against your skin.
Nothing is wrong. It's a different delivery method: instead of short bursts of very hot air, a heat pump moves a larger volume of mildly warm air over a longer period. The house arrives at the same temperature by a different route.
Long run times are also normal. A heat pump that runs for hours at a stretch in cold weather is doing its job. Furnaces cycle on and off; heat pumps are most efficient running steadily. If you're used to a furnace, the constant operation reads as a problem when it's actually the design working.
The test that matters isn't how the air feels. It's whether the thermostat reaches and holds its setpoint.
Defrost cycles look alarming and aren't
In cold, damp conditions the outdoor coil accumulates frost. To clear it, the heat pump briefly reverses — running in cooling mode to warm the outdoor coil and melt the ice off it. Backup heat usually covers the house while that happens.
What you'll notice:
- The outdoor unit stops, or the fan shuts off while the compressor keeps running
- Steam rising off the outdoor unit, sometimes a lot of it
- Cooler air indoors for a few minutes
- A whooshing or clunking sound as the reversing valve changes over
All normal. The steam in particular gets us called out fairly often, and it's just melted frost evaporating off a warm coil.
Defrost happens most in the 0 to −8°C damp range, which is exactly the weather a chinook brings. In a proper Calgary deep freeze the air is dry enough that frosting slows down. If your heat pump seems to defrost constantly in mild weather and rarely at −25°C, that's the reason.
What isn't normal is defrosting every few minutes, staying in defrost for a long stretch, or the outdoor unit encased in solid ice rather than light frost. That's a fault.
Below the balance point, backup has to take over
Every heat pump has a balance point — the outdoor temperature at which its output stops being enough to match your home's heat loss. Above it, the heat pump carries the house alone. Below it, something has to make up the difference.
Where that point falls depends on the equipment and the house. A properly specified cold-climate unit in a well-sealed home holds on far longer than an older or undersized one in a leaky house.
In Calgary this isn't optional. Our design temperature is −35°C, and no air-source heat pump carries a house alone at that. Backup — a gas furnace in a dual-fuel setup, or electric elements — is part of the system, not an admission of failure.
So if your house drifts cold specifically during a cold snap and is fine the rest of the winter, the question isn't "why is the heat pump failing." It's "why isn't the backup picking up?" That's usually one of:
- The dual-fuel switchover temperature is set too low, so the heat pump is being asked to work below its capability
- The furnace or electric backup isn't wired or configured to engage
- Auxiliary heat is locked out in the thermostat settings
- The system was never commissioned properly, so the changeover logic was left at a default that doesn't suit the house
All of those are setup problems rather than broken equipment, and all are correctable.
Real faults worth knowing
A dirty filter or blocked airflow. Same as any forced-air system. Restrict the air and output drops. Check it first — it's free and it's a common answer.
A dirty outdoor coil. The coil is how the system pulls heat out of outside air. Coated in dust, cottonwood fluff or grime, it can't. We've covered this in detail in how to clean heat pump coils, including what not to do.
Low refrigerant charge. Almost always a leak, because refrigerant isn't consumed. Capacity drops off and the system leans harder on backup. This needs a technician — it isn't a top-up-and-carry-on situation, because the leak will still be there.
A failed reversing valve. This is the component that switches the system between heating and cooling. Stuck in the wrong position, you get genuinely cold air on a heat call — not "cooler than a furnace" but actual air conditioning in January. Distinctive, and unmistakable once you know it exists.
The thermostat left on Emergency Heat. Em Heat bypasses the heat pump entirely and runs backup only. The house stays warm, so nobody notices — until the power bill arrives. Worth checking any time someone has been adjusting the thermostat.
Deep overnight setbacks. Heat pumps recover slowly by design. Setting back 5°C overnight the way you might with a furnace means the system either takes hours to catch up or calls in expensive auxiliary heat to do it. A heat pump prefers a steady setpoint, and this genuinely surprises people switching over from a furnace.
Ice on the outdoor unit
Light frost that comes and goes with defrost cycles is fine. A unit encased in solid ice is not, and it needs attention rather than time.
Common causes in Calgary:
- Snow drifted up around or over the unit, blocking airflow
- A roof drip line above the unit, dripping meltwater onto it that refreezes overnight
- The unit sitting too low, so it's standing in its own defrost meltwater
- A defrost control or sensor failure, so the cycle never runs
Two things you can safely do: clear snow from around and above the unit, and make sure there's clearance underneath so meltwater drains away. Outdoor units here should be on stands that keep them above expected snow depth, and if yours isn't, that's worth fixing before winter.
One thing not to do: don't chip ice off the coil. The fins bend if you look at them wrong and the refrigerant tubing sits right behind them. A screwdriver through a coil turns an inconvenient morning into a refrigerant leak and a much larger bill.
What to check before calling
- Thermostat is on Heat, not Em Heat or Cool, and the setpoint is above room temperature
- The filter — change it if it's dirty rather than looking at it hopefully
- Supply registers open, cold-air returns clear of furniture
- Snow and ice cleared from around, above and beneath the outdoor unit
- Whether the outdoor fan is actually turning
- Whether the house is reaching setpoint over a few hours, or genuinely falling behind
That last one is the real diagnostic. Air that feels cool but a house holding 21°C is a system working correctly. A house that keeps drifting down is a system that isn't.
When to call
Call if the house isn't reaching setpoint, if the outdoor unit is solid with ice, if you're getting genuinely cold air on a heat call, or if the backup seems to be running all the time.
That last one matters more than people realise. A heat pump leaning on auxiliary heat to cover a fault it should be handling itself will keep your house warm and quietly cost you a great deal over a winter. It's the failure mode nobody notices, because nothing feels broken.
If you're weighing up whether a heat pump suits your home in the first place, our comparison of heat pumps and furnaces in Calgary covers that side of it.
If your heat pump isn't keeping up, call 587-834-3668 and we'll check the charge, the defrost operation, and — the one that gets missed most — whether the changeover to backup was ever set up correctly for your house. See our heat pump page for the full scope.
