A heat pump can feel a little mysterious in winter, especially if you grew up with a traditional furnace. You hear it run longer, feel milder air at the vents, and wonder if it can really keep up when cold settles in. At Green Dot Heating & Air in Wilmington, NC, we walk you through how a heat pump works so that you know what normal winter operation looks like.
How a Heat Pump Moves Heat in Cold Weather
A heat pump does not create heat the way a furnace does. It moves heat from one place to another. In winter, that means pulling low-level heat from outside air and carrying it indoors. Even when the air feels very cold to you, it still holds energy. The outdoor unit collects that energy and sends it inside through a closed refrigerant loop. The indoor unit then releases that heat into your ductwork or air handler so that warm air flows through the house.
The refrigerant is the working fluid that makes this possible. It travels in a loop through copper lines and passes through different components that change its pressure and temperature. In heating mode, the outdoor coil acts like an evaporator. It takes in liquid refrigerant at low pressure, which absorbs heat from the outside air and turns into a gas. The compressor pulls in that low-pressure gas and squeezes it. Pressure rises, and so does temperature. Now you have a hot, high-pressure gas ready to deliver heat inside.
The Reversing Valve: Switching Between Heating and Cooling
The part that turns a standard-looking air conditioner into a heat pump is the reversing valve. This valve, located in the outdoor unit, reverses the direction of refrigerant flow. In summer, the system works like a regular air conditioner. The indoor coil absorbs heat from indoor air and sends it outside, where the outdoor coil releases that heat. In winter, the reversing valve shifts positions. Now the outdoor coil becomes the place where refrigerant picks up heat, and the indoor coil becomes the place where heat leaves the refrigerant and enters your home.
The thermostat sends a signal that tells the system whether you want heating or cooling. That signal triggers the reversing valve to move to the correct position. You may hear a brief whoosh or change in sound when the valve shifts as the system goes from one mode to the other. A technician checks this valve during a service visit to make sure it slides smoothly and seals properly. If the valve sticks, you might feel lukewarm air at the vents or notice that the system struggles to switch seasons. That is not a repair to handle yourself, since it involves refrigerant, electrical controls, and careful testing.
How a Heat Pump Differs From a Furnace or Standard AC
A traditional furnace burns fuel or uses electric resistance to create heat. In a gas furnace, burners light, heat passes through a heat exchanger, and a blower moves that heated air through ducts. Supply air feels noticeably hot when you place your hand at a register while the furnace runs. The air comes out in strong bursts, then the system shuts off once the thermostat reaches its setting. With electric resistance heat, strips warm up inside the air handler and create heat through electrical resistance, with similar on and off cycles.
A heat pump usually sends out air that feels milder. It may feel closer to the temperature of a warm bath than a hot oven. That does not mean the system has failed. It runs longer on purpose, moving modest heat for a longer period rather than firing in short bursts. The upside is that you often see more stable room temperatures and can save energy compared to electric resistance heat. The difference shows up on your thermostat and at the registers. You may notice fewer wild swings between warm and cool in the same room when the heat pump is set up and maintained correctly.
Cold Climate Heat Pumps and Backup Heat
Heat pumps work best when outdoor temperatures stay in a range that still holds a decent amount of energy in the air. In many regions, standard models perform well down to the low 20s before their output falls off. Modern cold-climate heat pumps push that boundary lower. They use advanced compressors, thoughtful coil design, and precise controls to pull heat from air that feels bitterly cold. In some setups, they can still move useful heat even when the outdoor air dips below zero degrees Fahrenheit.
That said, every system has limits. At a certain point, the heat pump does not have enough capacity to keep up with your house’s heat loss on its own. That is where backup heat comes in. Some homes pair a heat pump with a gas furnace in a dual fuel setup. Others use electric resistance strips inside the air handler as supplemental heat. Controls switch to that backup source when the outdoor temperature and load call for it. A professional sizes the equipment, sets balance points, and programs controls so that the transition feels smooth. You set your thermostat, and the system chooses the most effective source for the conditions outside.
Defrost Cycles and What “Normal” Looks Like Outside
One of the strangest winter behaviors you might notice is frost or light ice on the outdoor unit. This surprises many homeowners the first time they see it. In heating mode, the outdoor coil runs colder than the air around it. Moisture in the air can condense and freeze on those cold fins, especially on damp, chilly days. A thin layer of frost is normal. If that frost builds up too thick, it can block airflow and reduce performance, so the system has an automatic way to handle it.
During a defrost cycle, the controls briefly switch the system into a form of cooling mode to warm the outdoor coil while the outdoor fan stops. This melts the frost so that air can flow freely again. You might hear a change in sound, see steam rise from the unit, or feel slightly cooler air at the indoor vents for a short period. That is part of normal operation. If heavy ice stays on the unit for long stretches or you see the fan blades frozen in place, that calls for a service visit. Avoid chipping ice or pouring hot water on the unit since that can damage coils, fan blades, or housing.
Keep Your Heat Pump Ready for Winter Weather
Understanding how your heat pump moves heat in cold weather helps you use it the way it was designed. When you pair that knowledge with seasonal maintenance, clean filters, and simple thermostat habits, you give the system a fair chance to heat your home efficiently. If you are ready to get your heat pump set for winter, schedule your next service visit with Green Dot Heating & Air today.
