Short answer
A heat pump that blows air that feels cool in winter or steams during defrost is often working normally. Problems to act on: the house can't hold temperature, the outdoor unit stays encased in ice, the thermostat shows aux heat running constantly, or the power bill spikes. Those point to a failed defrost control, a refrigerant leak, a reversing valve problem, or a thermostat setup issue.
Most heating calls here in winter are really heat pump calls. At GSP, January lows average 32.1°F and July highs average 90.3°F (National Weather Service, 1991–2020 normals). That's a real load in both directions, and it's why a heat pump makes sense in this climate, and why it wears.
First: what's normal
Every Upstate homeowner with a heat pump should know these, because they save a service call:
- The air feels cooler than a furnace. A heat pump delivers a lot of warm air at a lower temperature than a gas flame. If the house is holding the setting, it's working.
- It runs for long stretches in cold weather. As it gets colder outside, a heat pump has less heat to move, so it runs longer. That's by design.
- Defrost cycles. In cold, damp weather frost builds on the outdoor coil. The system reverses for a few minutes to melt it. You'll see steam, the outdoor fan stops, and there's a whoosh when it switches back.
- Aux heat in short bursts. Electric heat strips help out during defrost and on the coldest mornings.
What's usually wrong
Aux heat running all the time
If the heat strips are carrying the load, the heat pump itself isn't doing its job, or the thermostat isn't set up for a heat pump. It's one of the most common causes of a shocking January bill. See aux heat and a high winter bill.
A defrost problem
A failed defrost board, sensor or relay lets ice build until the outdoor coil is a block. Heating drops off, and the strips take over.
Reversing valve or its solenoid
The reversing valve switches the system between heating and cooling. When it sticks, you get cooling in heating mode or the other way around.
Low refrigerant
A heat pump uses refrigerant in both seasons, so a leak shows up as weak heating and weak cooling. Low refrigerant always means a leak.
Capacitors, contactors and motors
The same outdoor electrical parts that fail on an AC fail on a heat pump, and a heat pump runs them year-round.
What we check on a service call
- Thermostat type, settings, and whether it's configured for a heat pump with aux heat staged correctly.
- Outdoor unit operation in heating mode: fan, compressor, capacitor and contactor.
- Defrost operation: the board, sensor, and whether the coil clears.
- Reversing valve operation in both modes.
- Refrigerant readings, and leak checks if they're off.
- Indoor unit: blower, filter, coil, and the heat strips and their controls.
- What we found and what the fix is, in plain words.
What it costs
Ask what the service call costs when you call. For what drives the price of a repair or a new system, see what HVAC work costs.
Repair or replace
Because a heat pump runs in both seasons, it tends to reach replacement age sooner than an AC that sits idle all winter. A failed compressor or a leaking coil on an older heat pump is usually the point to price a replacement. If replacement comes up, the same rules apply as for an AC: size it to the house, get the model numbers in writing, and know exactly what's included. See installation and replacement.
If you have gas at the house, a dual-fuel setup pairs a heat pump with a gas furnace that takes over in the coldest weather. Whether that pays off depends on your house and your gas service, and it's worth asking about.
Local detail
Heat pumps dominate Upstate subdivisions, and many of their air handlers sit in crawlspaces or attics. A crawlspace air handler sits in damp air, and a clogged drain there doesn't show up on a ceiling, so it can go unnoticed. If you haven't looked at yours in a while, a fall heating check is the time.
Common questions
Why does my heat pump blow cool air in winter?
Air from a heat pump is warmer than the room but cooler than your skin, so it can feel cool against your hand compared with a gas furnace, even while it is warming the house. During a defrost cycle the system also runs briefly in cooling mode to melt frost off the outdoor coil. If the house is holding temperature, that is normal. If the house keeps losing ground, something is wrong.
Is it normal for my heat pump to steam or make a whooshing sound?
Yes, during defrost. The outdoor unit reverses for a few minutes to melt frost, and you may see steam and hear the fan stop and a whoosh when it switches back. A unit that stays encased in ice is not normal.
What is auxiliary heat on my thermostat?
Auxiliary (aux) heat is a set of electric resistance heat strips in the indoor unit that help the heat pump in very cold weather or when the house needs to warm up quickly. It is normal in short bursts. Running constantly, it can make your power bill jump.
What is emergency heat and when should I use it?
Emergency heat turns off the heat pump and heats the house with the electric strips alone. Use it only if the outdoor unit has failed, and call for a repair. Left on, it is an expensive way to heat a house.