Heat Pumps in Northwest Winters: What's Normal and What Isn't

A heat pump heats your house by moving heat from the outdoor air to the inside. Even cold air holds some heat. The heat pump's refrigerant picks it up outside and releases it indoors. In summer, the system runs the other way and cools your home.

Because it moves heat instead of burning fuel, ENERGY STAR says an air-source heat pump can deliver up to three times more heat energy than the electrical energy it uses. The U.S. Department of Energy says that in moderate climates, heat pumps can be an energy-efficient alternative to furnaces and air conditioners.

Heat pumps come in two main styles. Ducted systems use the same ducts a furnace would. Ductless systems, often called mini-splits, use indoor heads mounted on a wall or ceiling.

Heat pump air often feels cooler at the vent than furnace air, and that's usually normal. A heat pump tends to deliver warm air in longer, steadier cycles. A gas furnace delivers hotter air in shorter bursts.

The test is the room, not the vent. If the house holds the temperature you set, the heat pump is doing its job. If the house keeps falling behind the thermostat, that's worth a closer look. Try not to judge it in the first few minutes after it starts. Signs it's working normally:

Defrost mode is how a heat pump clears frost off its outdoor coil, and a little steam is a normal part of it. In cold, damp weather — the kind Northwest winters bring — frost can build on the outdoor unit as it pulls heat from the air. Every so often, the system briefly reverses to warm the coil and melt the frost.

During defrost you may notice the outdoor fan stop, a whoosh or click as the system switches, steam rising off the unit, and water dripping below it. Indoors, backup heat may come on briefly so you don't feel cool air. Then the system goes back to normal heating.

Most heat pumps keep heating through a cold snap, but they may need help from backup heat. As outdoor air gets colder, there's less heat to move, and the heat pump works harder. Many systems have backup heat — electric heat strips or a gas furnace — that steps in when the heat pump can't keep up on its own.

When backup heat runs, your thermostat may show AUX. That's normal in very cold weather. It's also why your bill may rise during a cold stretch: electric backup heat usually costs more to run than the heat pump does.

Our region's winters are mostly wet and mild, with occasional cold snaps. That mix is where a working defrost cycle and properly set-up backup heat matter most.

A cold-climate heat pump is one built and tested to keep heating well at low outdoor temperatures. ENERGY STAR says many newer certified models use advanced compressors and refrigerants that improve low-temperature performance.

ENERGY STAR's cold-climate certification requires third-party verified testing down to 5°F. These units keep running below that, but ENERGY STAR notes that pairing one with a backup heat source heats the home most efficiently when it's even colder.

If you're choosing a new heat pump, ask whether a cold-climate model fits your home, and how backup heat will work with it. ENERGY STAR also says a contractor should size the system with a Manual J load calculation. A system that's too big or too small will struggle to keep you comfortable.

Pick a comfortable temperature and leave it there. ENERGY STAR says heat pumps, unlike furnaces, don't save energy when you turn them down at night or while you're away. A deep setback can also make backup heat run to catch up in the morning.

These settings help your heat pump do its job:

A winter heat pump problem is worth a call when the house won't hold temperature or the outdoor unit stays iced. Try the safe checks below first. If they don't fix it, leave the rest for a technician.

Call if the outdoor unit is encased in ice, AUX shows almost all the time in mild weather, the outdoor fan won't run, you hear grinding or loud banging, or a breaker trips a second time.