A heat pump AC unit is a reversible HVAC system that moves heat instead of generating it, cooling your home in summer and warming it in winter through the same equipment.
One system does both jobs. A heat pump runs refrigerant through a compressor, two coils, and a reversing valve — the same parts as a standard air conditioner, plus the valve that flips heat flow. That single addition changes what the machine can do: instead of throwing away its cooling hardware when the temperature drops, it keeps working.
How Does A Heat Pump Move Heat In Both Directions?
The reversing valve changes which coil acts as the evaporator and which as the condenser, so the same loop can pull heat out of your rooms or push it in.
In cooling mode, the indoor coil absorbs heat from your air and the refrigerant carries it to the outdoor coil, where a fan releases it outside. In heating mode, the valve swaps the flow: the outdoor coil extracts whatever heat exists in the outside air, even when it’s cold, and the indoor coil releases it into your home.
The compressor pressurizes refrigerant and raises its temperature; the expansion valve drops the pressure and temperature so the refrigerant can absorb heat on the next pass. Fans move air across both coils, and conditioned air arrives through ducts from an air handler or straight from a wall-mounted indoor unit. Because the system relocates heat rather than burning fuel, it can deliver more heating energy than the electricity it consumes.
What Do COP, EER, And HSPF Actually Tell You?
Coefficient of performance compares heating output to electrical input, and heat pumps routinely land between 2 and 5 — two to five units of heat per unit of electricity. A typical gas furnace sits near 0.8 by the same measure, per DOE training material.
EER rates cooling efficiency under fixed test conditions. HSPF rates heating efficiency across a season. A DOE publication lists historical HSPF bands of 6.6 to 6.8 for certain minimum-efficiency single-package and split systems, 7.2 to 7.8 as medium efficiency, above 8.0 as high efficiency, with variable-speed systems reaching 10. Treat those as reference points, not a current national purchasing standard.
| System Type | How It Moves Heat | Where It Fits |
|---|---|---|
| Ducted air-source | Outdoor unit tied to an indoor air handler and ductwork | Homes with existing ducts |
| Ductless mini-split | Outdoor unit feeding one or more wall or ceiling heads | Additions, rooms without ducts |
| Cold-climate air-source | Air-source design built for lower outdoor temperatures | Colder regions, model-dependent |
| Geothermal (ground-source) | Exchanges heat with soil or groundwater via ground loops | Sites where loop installation works |
Geothermal systems hold a clear efficiency edge because ground temperatures stay stable year-round. DOE states ground-source heat pumps may cut energy use by roughly 25% to 50% compared with air-source units and can reach 300% to 600% efficiency under specified conditions.
Where Does Cold Weather Limit Performance?
Heating capacity and efficiency both fall as outside air gets colder, because there’s less heat to extract. That’s physics, not a defect. Cold-climate models are engineered for lower temperatures, though exact performance depends on the model and installation. Many setups pair the heat pump with an auxiliary heat source that kicks in when conditions exceed the system’s practical heating capacity — on a thermostat, that shows up as auxiliary or emergency heat mode.
Sizing matters as much as equipment. Correct sizing comes from the building’s design heating and cooling loads, never from square footage alone. Replacing an old air conditioner with a heat pump of the same nominal tonnage, without a load calculation, is one of the most common and most expensive mistakes.
Weighing specific equipment? Our roundup of tested AC heat pump units compares models on capacity and cold-weather ratings.
What Does Installation And Upkeep Require?
Refrigerant work belongs to a licensed HVAC technician — improper charging or connections can hurt performance and create safety and environmental hazards. Everything else is mostly about airflow.
DOE training material notes that HVAC systems may not perform as designed without correct installation, programmed controls, and commissioning. Maintenance keeps the numbers honest: clean or replace filters, keep coils clear, verify airflow, check controls, and leave clearance around the outdoor unit. The sources reviewed don’t fix one universal filter interval, so follow your manufacturer’s schedule.
A heat pump is not just an air conditioner with a different label — it heats as well as cools, so equipment, controls, and sizing are all evaluated differently than a straight AC replacement. The DOE geothermal heat pump overview lays out how the ground-source version differs from air-source equipment.
FAQs
Is a heat pump the same thing as an air conditioner?
No. Both use a compressor, coils, and refrigerant, but a heat pump adds a reversing valve that lets refrigerant flow in either direction, so it cools in summer and heats in winter. An air conditioner only removes heat from your home and cannot run the cycle backwards to warm it.
Do heat pumps work in freezing weather?
They do, though heating capacity and efficiency drop as outdoor air gets colder because less heat is available to extract. Cold-climate models are built for lower temperatures. Many systems also include an auxiliary heat source that engages when conditions exceed the heat pump’s practical heating capacity.
How much can a geothermal system save compared with air-source?
DOE states ground-source heat pumps may reduce energy consumption by approximately 25% to 50% compared with air-source heat pumps, and can reach 300% to 600% efficiency under specified conditions. Actual results depend on climate, ground conditions, loop design, and how well the system is sized and installed.
References & Sources
- U.S. Department of Energy. “About Air Source Heat Pumps Handout” Supports the vapor-compression cycle explanation, COP figures, and installation guidance.
- U.S. Department of Energy. “Geothermal Heat Pumps” Supports ground-source efficiency comparisons and the 25%–50% energy reduction figure.