Heat pump
An HVAC system that both heats and cools by moving heat instead of burning fuel.
A heat pump is an HVAC system that works in both directions: in summer it pulls heat out of your home like an air conditioner, and in winter it runs in reverse to pull heat in from outside. Because it moves heat rather than generating it, it's very efficient. The trade-off is that it needs the same care as an AC — clean filters, clear the outdoor unit, and an annual tune-up — plus the outdoor coil must stay free of snow and ice in winter.