Dual fuel
A hybrid HVAC setup that pairs an electric heat pump with a gas furnace and switches between them.
A dual-fuel (or hybrid) system combines an electric heat pump with a gas furnace and switches automatically based on the outdoor temperature. On mild and moderate days the heat pump heats efficiently and cheaply; once it drops below a set 'balance point,' the gas furnace takes over because it's cheaper and stronger in deep cold. Dual-fuel shines in cold climates where you want heat-pump efficiency most of the year but reliable furnace heat in a hard freeze. The trade-off is higher upfront cost and two heating sources to maintain instead of one.