♨️What does a heat pump cost to run?

Coefficient of performance: units of heat delivered per unit of electricity consumed. A resistance heater is exactly 1. An air-source heat pump is typically 2.5 to 3.5 in mild weather. It matters more than the wattage because it is the multiplier between what you pay for and what you get — the same 1,200 W of electricity buys three times the warmth.

It depends entirely on the ratio between your electricity and gas prices. As a rule of thumb, a heat pump at COP 3 beats a 90% efficient gas boiler when electricity costs less than about 3.3 times gas per unit of energy. In the US that usually favours the heat pump; in parts of Europe where electricity carries heavy levies, it can be close.

Modern ones do not stop, they slow down. Capacity and COP both fall as the outdoor temperature drops; cold-climate models hold most of their output down to −13 °F. What changes is the economics: below the balance point, backup resistance heat runs at a COP of 1 and every hour of it costs about three times as much.

The specification sheet lists input power in watts or kilowatts at the rating condition, separately from heating capacity. If you only have the heating output and a COP, divide: 12,000 BTU (3.5 kW) of heat at COP 3 is about 1,170 W drawn. A clamp meter or the utility’s smart meter data settles it for a whole house.

A little less, usually. In cooling mode the same machine typically runs at an efficiency ratio equivalent to a COP of 3 to 4, so summer running costs land close to or slightly below winter ones for the same hours. The bigger seasonal difference is how many hours it runs, not what it costs per hour.

Against electric resistance heating, the saving is roughly two thirds of the heating bill, which usually pays back a mini split within a few winters. Against gas, the payback depends on your local price ratio and can be much longer. The calculator here gives you the running side of that sum; the installed price is a quote, not a formula.