# What is a heat pump, and how can the same unit heat and cool?

**Short answer:** A heat pump is an air conditioner with a reversing valve. Cooling has always worked by moving heat from inside to outside; a heat pump can flip the direction and move heat from outside air into the house in winter. Moving heat costs far less than making it, which is why heat pumps heat so cheaply, and why mild-winter Bakersfield is nearly ideal territory for them.

The name does the technology no favors. "Heat pump" sounds like a furnace accessory, when the truthful name would be "two-way air conditioner," because that is the entire trick, and once you see it, every confusing thing about heat pumps makes sense.

**Start with what your AC already does:** an air conditioner does not create cold. It collects heat from your indoor air and pumps it outside, using refrigerant as the carrier, which is why the outdoor unit blows hot air in July: that is your living room's heat being thrown away. Every AC is already a heat-moving machine pointed in one direction.

**The heat pump's one extra part:** a reversing valve that flips the direction of flow. In winter the machine collects heat from outdoor air, and yes, 45 degree air contains plenty of heat by physics' accounting, and pumps it indoors. Same compressor, same refrigerant, same two boxes, running the loop backwards. Summer performance is identical to an equivalent AC because in summer it simply is one.

**Why this heats so cheaply:** a gas furnace and [an electric space heater](/answers/is-it-cheaper-to-run-space-heaters-or-central-heat/) both make heat, paying full price for every unit. A heat pump merely relocates heat that already exists outside, delivering two to three units of warmth per unit of electricity purchased. That leverage is the entire economic argument, and it is strongest in climates where winter is mild and the machine rarely strains, which is a description of Bakersfield: our winters ask so little that [the heating fight here is a fair one](/answers/heat-pump-vs-gas-furnace-in-bakersfield/), while the summers get a machine identical to a high-efficiency AC.

**The quirks that confuse new owners, all normal:** the air from the vents feels [warm rather than hot](/answers/why-does-my-heat-pump-blow-lukewarm-air/), the outdoor unit runs in winter and occasionally [steams during defrost](/answers/why-does-my-heat-pump-blow-lukewarm-air/), and the thermostat carries [an emergency heat setting you should mostly ignore](/answers/what-is-emergency-heat-on-my-thermostat/).

**Where you already own one:** every [mini split](/answers/do-mini-splits-work-in-bakersfield-heat/) is a heat pump, which is why one wall unit handles a garage conversion year-round. Full-size systems run $9,800 to $14,200 installed, replace the furnace and AC in one box, and currently carry federal credits up to $2,000, paperwork ours. Whether one beats gas for your specific house is a math conversation we will happily lose when the math says to.

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