Heat Pump

Definition

A heat pump runs the same refrigeration cycle as an air conditioner — compressor, condenser coil, expansion device, evaporator coil — but adds a reversing valve that lets the refrigerant flow either direction. In cooling mode it pulls heat out of indoor air and dumps it outside (just like an AC). In heating mode it reverses direction, pulling heat out of outdoor air and dumping it inside.

That "pulling heat out of cold air" sounds counterintuitive, but at 35°F there's still enormous thermal energy in the air relative to absolute zero — the refrigerant just operates at a colder temperature so heat flows the right way. Modern variable-speed heat pumps maintain near-full HSPF2 efficiency above ~25°F outdoor; below 20°F they progressively rely on backup electric heat strips.

Two heat pump form factors are common in Austin: central ducted heat pumps (look and install like a regular AC + furnace combo, except the indoor coil is paired with an air handler) and ductless mini-splits (no central duct system; one outdoor unit feeds one or more wall- or ceiling-mounted indoor heads).

Why it matters in Austin

The economics of heat pumps in Central Texas are unusually favorable. We have long cooling seasons, short mild winters, and a high cooling-degree-day to heating-degree-day ratio. One efficient heat pump beats running a separate AC and gas furnace on combined operating cost, and it qualifies for Austin Energy rebates plus the federal IRA HEAR program.

The exception is if your home doesn't have a gas line and you'd otherwise need to add one — heat pumps skip that. The other exception is if your existing gas furnace is brand-new and you only need to replace the AC side; in that case, sticking with a gas/AC split makes more sense.