Cold climate heat pumps: how they really perform in Pacific Northwest winters.

What is a cold climate heat pump?

A cold climate heat pump is an inverter-driven heat pump built to keep heating in hard cold, and the term has a public test. To be on the Northeast Energy Efficiency Partnerships (NEEP) list of cold-climate air-source heat pumps, a system has to be variable-capacity (inverter-driven), publish its capacity and efficiency at 5°F, and hold a coefficient of performance (COP) of at least 1.75 at 5°F. A COP of 1.75 means 1.75 units of heat for every unit of electricity, 75% more heat per dollar of power than electric baseboard or a furnace heat strip.

What makes it work is the compressor. A standard single-speed heat pump runs at one output and loses capacity as the air gets colder. An inverter compressor speeds up as the temperature drops, so the unit can keep delivering its rated heat when you need it most. That is how Mitsubishi's Hyper-Heat line holds 100% capacity at 5°F.

How cold is "cold" in Vancouver?

Vancouver WA's heating design temperature is about 24°F, the ASHRAE 99.6% value for Pearson Field. A design temperature is the outdoor temperature that only a small fraction of winter hours drop below, and a proper Manual J load calculation sizes the system to a design temperature like this one.

Cold snaps go lower than design, which is what the margin is for. The February 2021 ice storm bottomed out in the mid-20s in Portland, and Portland's all-time record low is -3°F, set in February 1950. A cold climate heat pump rated to -13°F still has headroom below the coldest day on record here.

How cold can a heat pump work?

How cold a heat pump can work depends on the model: Mitsubishi rates its standard WX-series ductless unit to heat down to 5°F, and its cold climate H2i sumo FX-series holds 100% of its heating capacity at -10°F and is guaranteed to run down to -22°F. A standard heat pump keeps heating below freezing but loses output as it gets colder.

What Mitsubishi and American Standard, the two brands we install, publish:

Every unit in the table keeps running at Vancouver's design temperature of about 24°F. What changes is how much heat is left. The standard unit is well below its rated output by 17°F, so it has to be sized bigger or lean on backup heat on the coldest days, while a cold climate unit still has its full output. ENERGY STAR tests cold climate models down to 5°F and notes they keep working below it. Our ductless mini-split page shows the systems we install.

Heat pump efficiency in cold weather, by temperature.

A heat pump gets less efficient as the outdoor temperature drops, but Mitsubishi's cold climate FX-series stays far above electric resistance heat down to -10°F. Mitsubishi rates its H2i sumo FX-series at a COP of 4.2 at 47°F, 2.48 at 17°F, 2.2 at 5°F and 2.0 at -10°F. At ten below zero it still makes twice the heat per kWh of a baseboard heater.

The heat pump figures come from each unit's Mitsubishi submittal; at 17°F and below they are measured at maximum output. For its Cold Climate designation, ENERGY STAR requires a COP of at least 1.75 at 5°F and at least 70% of the unit's 47°F heating capacity still available at 5°F.

What that means on a Clark County bill: at Clark PUD's 8.79¢ per kWh and NW Natural's $1.506 per therm, a heat pump makes heat for less than a 95% AFUE gas furnace whenever its COP is above about 1.6. Every heat pump figure in the table clears that line. Baseboard heat at COP 1.0 costs about 60% more per unit of heat than the gas furnace. Our dual-fuel guide walks through the math.

Will a heat pump use backup heat constantly?

No. Electric backup heat (a heat strip) only runs when the heat pump can't keep up, or during defrost on ducted systems. In a correctly sized cold climate installation in our climate, that is a small slice of the winter. Where homeowners see big backup-heat bills, the cause is almost always an undersized system or a thermostat set up to call for backup heat too early. In a dual-fuel system, the gas furnace also runs whenever it is colder than the switchover temperature set on the thermostat.

Can a heat pump keep up during cold snaps?

A properly sized cold climate heat pump handles cold snaps fine; an undersized heat pump can't keep up.

If a contractor sizes your heat pump at "3 tons because the old furnace was 3 tons," you might have capacity issues in a February cold snap. If they calculate the design-temperature heating load for your specific home (insulation, air leakage, window area, orientation), you get a unit that matches the need. Every heat pump we quote includes a Manual J load calculation.

Do defrost cycles blow cold air into the house?

Not on a properly set up system. In cold, damp weather, frost builds on the outdoor coil, and every heat pump periodically runs a short defrost cycle to melt it. On ducted systems, the backup heat strip (or furnace) usually comes on during defrost so the air from the vents stays warm. Ductless indoor heads pause their fan for those few minutes instead of blowing cool air. You may hear a whoosh from the outdoor unit and see some steam; both are normal.

What actually limits a heat pump in Vancouver.

Four things actually limit a heat pump in Vancouver:

• Electrical service capacity. Heat pumps pull more amps than a gas furnace, and older 100-amp panels sometimes need an upgrade. We check the panel on the site walk and price any electrical work in the written quote.
• Outdoor unit placement. It needs clear airflow and should sit on a raised stand so snow and ice don't pack the coil. In east-county spots that catch the Gorge wind, we keep it out of the direct wind where we can.
• Refrigerant line length. Long runs from outdoor to indoor unit reduce efficiency. Most homes are fine; a few need care.
• Installer skill. Cold climate heat pumps have tighter installation tolerances than basic equipment, so commissioning matters. Factory-trained contractors, such as Mitsubishi Diamond Contractors, carry the longer warranty for that reason.

How to run a heat pump in cold weather.

To run a heat pump in cold weather, set the thermostat where you're comfortable and leave it there. Heat pumps are most efficient holding a steady temperature and warm a house back up slowly, so a big overnight setback makes it hard for the system to catch up in the morning. Mass Save, the Massachusetts utilities' efficiency program, recommends setbacks of 2–3 degrees at most.

• Keep changes small. The Consortium for Energy Efficiency's owner guide says to avoid changes of 3°F or more while you're out and to save bigger setbacks for absences longer than a day.
• Leave it in Heat. "Auto" can switch to cooling on a sunny winter afternoon. If the thermostat shows auxiliary heat on most of the time in mild weather, have it checked: aux is electric strip heat at COP 1.0, and constant aux is a sign something is off. Our heat pump repair techs can trace it.
• Lukewarm air below freezing is normal. Heat pump supply air typically runs about 85–105°F, against 120–160°F from a gas furnace, and it can drop as the outdoor temperature drops. In very cold weather the system may also run almost nonstop. Both are fine as long as the house holds its setpoint.
• Keep the outdoor unit clear. Don't cover it for winter. Keep snow off it and roof runoff from dripping onto it.
• Gas furnace as backup? A properly sized heat pump doesn't need one to keep up here. If you have a working furnace, a dual-fuel setup can hand it the coldest hours. On its own thermostat, the CEE guide suggests setting the furnace 2–4 degrees below the heat pump so it only runs when needed.

Curious how a cold climate heat pump would perform in your home? Request a quote and we'll size it to your home's actual heating load and show the expected operating cost in writing.

Questions homeowners ask.