Heat pump vs furnace: what actually changes in your home

If you've only ever lived with a furnace, switching to a heat pump comes with a learning curve. Most of it is in your favour. The equipment is quieter, the temperature is more even, and the unit usually does both heating and cooling. But a few things are genuinely different, and the differences are worth knowing before you sign a contract.

The air coming out of the registers is cooler

This is the change new heat pump owners notice first. A gas furnace's supply air is around 45°C, hot enough to feel obviously warm when you stand near a register. A heat pump's supply air is around 32°C, which is warmer than the room but cooler than your skin.

People standing in front of a vent often think the heat pump isn't working. It is. It's delivering the same amount of heat per hour as the furnace, just at a lower temperature and higher airflow rate. The total heat delivered to the room is identical. The sensation of "warm air" at the vent is what changes.

This takes a few weeks to get used to. After that, most people prefer it: the temperatures across the home are more even because the air doesn't have to be as hot to do its job.

The system runs more of the time

A furnace cycles. It comes on, runs at full output for ten or fifteen minutes, shuts off, waits, comes on again. You hear it start and stop several times an hour.

A properly-sized heat pump runs continuously through cold weather, at part load. You hear a quiet hum that doesn't stop. The compressor speed varies with demand: faster when it's colder outside, slower when it's milder.

The continuous operation is actually the heat pump's natural mode. Modulating output is what variable-speed inverter compressors do, and they're more efficient running steadily than cycling. But homeowners coming from a furnace sometimes worry that "it never shuts off." It's supposed to do that.

You hear different sounds

A gas furnace has a burner, a flame, and a flue. None of those sounds exist with a heat pump. What you hear instead is the outdoor unit's compressor, the outdoor fan, and the indoor air handler's fan. The outdoor unit is usually mounted next to the house and produces a noise similar to a central air conditioner. Most modern units are in the 50–60 dB range at one metre. Quieter than a refrigerator, louder than a whisper.

The outdoor unit also goes through periodic defrost cycles. When the outdoor coil ices up (which happens at temperatures between –5°C and +5°C), the unit reverses briefly to melt the ice. During defrost, the unit makes a slightly different sound, the outdoor fan stops, and you might see a brief puff of steam from the outdoor unit. This is normal. The cycle lasts a few minutes and then heat resumes.

You may need an electrical service upgrade

A gas furnace uses minimal electricity. Just enough to run the blower fan and the ignition. A heat pump runs entirely on electricity, and the compressor plus any backup heat strips can pull 30 to 60 amps under heavy load.

Many older Canadian homes have a 100-amp electrical service. With electric water heating, an electric dryer, an electric stove, and now a heat pump with backup heat, the existing panel can be at its limit. Some homes need to upgrade to a 200-amp service before the heat pump can be installed, which adds $2,500 to $5,000 to the project.

Some heat pumps avoid this with a "smart" or "load-managed" backup that automatically reduces other loads when the backup heat is running. Others use a smaller backup or no backup at all (in which case the original furnace stays as the backup). A good contractor will assess your panel before quoting and tell you whether an upgrade is part of the job.

The thermostat acts differently

A traditional thermostat tells a furnace "turn on" and "turn off." Heat pumps have more nuance: the thermostat may also signal "boost to higher capacity," "engage backup heat," "enter defrost," and so on. Many older thermostats can't drive a heat pump properly. The install usually includes a new heat-pump-compatible thermostat.

The setback strategy also changes. With a furnace, you can let the temperature drop 4°C at night and the furnace will easily recover in the morning. With a heat pump, deep setbacks are counterproductive because the unit has to run backup heat to catch up quickly, which costs more than just maintaining temperature would have. The general rule is: set the temperature you want, and leave it. The continuous operation handles the rest.

You don't need a furnace exhaust or fresh air for combustion

Removing the furnace removes the flue, the combustion air intake, and the gas line (if you're switching from gas). This frees up some basement space and eliminates a small carbon monoxide risk. It also means one less appliance that needs annual inspection.

If you keep the furnace as backup for cold nights (dual-fuel setup), the flue and gas line stay. The carbon monoxide detector requirement stays. The annual inspection requirement stays. You've added a heat pump rather than fully switched, with both pros and cons.

Summer is part of the deal

A heat pump is also a central air conditioner. If your house previously didn't have AC, summer suddenly gets more comfortable. If you previously had a window unit or a central AC, you can remove it: the heat pump does the same job.

For households in southern Ontario, the southern Prairies, and parts of British Columbia, where summer cooling demand is meaningful, this is a hidden value the cost calculations sometimes miss. A heat pump install often eliminates the future replacement cost of a separate AC, which can be $4,000 to $7,000 by itself.

The maintenance is similar but different

A furnace needs an annual inspection by a licensed technician. The combustion is cleaned, the flue is checked, the heat exchanger is examined for cracks.

A heat pump doesn't have combustion, so there's no flue or burner to service. But the refrigerant lines, the outdoor coil, the indoor coil, and the condensate drain all need periodic attention. Most manufacturers recommend annual service. The cost of a heat pump tune-up is comparable to a furnace tune-up, usually $150 to $250.

One additional task that homeowners can do themselves: keep the outdoor unit free of snow and ice in winter, and clear of leaves and debris in summer. Snow piled around the unit reduces airflow and forces it to work harder. Most installs include a small platform that keeps the unit above typical snow line. If yours doesn't, ask for one.

Cold-weather behaviour

A furnace's output doesn't depend on outdoor temperature. At –30°C or +10°C, it delivers the same heat per hour.

A heat pump's output drops as outdoor temperature falls. Below the unit's balance point (typically –10°C to –20°C), it can no longer keep up with the home's heat loss on its own, and the backup heat (electric resistance or the original furnace) has to engage. This is by design. The economics of heat pumps depend on running them when they're efficient, and using backup heat for the small number of hours when they aren't.

What you experience is: most of winter, the heat pump handles everything quietly. On the coldest nights of the year, the backup kicks in. If the backup is electric resistance, your electricity bill spikes for a few days. If the backup is a furnace, your gas or oil bill includes a small amount of fuel use during the coldest snap. Either way, those few days don't change the annual math significantly.

The summary

A heat pump is not a quieter, cleaner furnace. It's a different machine that does the same job by different means, with different operating characteristics. Most of those characteristics are improvements: quieter, more even heating, summer cooling included. A few are adjustments: the supply air feels cooler, the system runs continuously, the thermostat strategy changes.

None of the changes are problems if you know about them in advance. They become problems when a contractor installs a heat pump without explaining what to expect and the homeowner spends six weeks worrying the equipment is broken when it's actually working perfectly.