How can a water heater deliver more heat than its electrical energy input?

A heat-pump water heater can transfer more thermal energy to water than the electrical energy it uses. Its extra input comes from the surrounding air. The device moves existing energy as well as receiving work from electricity, so no energy has to be created.

Refrigerant circulates through a closed route. In an air-side coil, it evaporates while absorbing energy from the room. An electrically driven compressor raises the vapor’s pressure and temperature. At the tank-side coil, the hotter refrigerant releases energy to the water and condenses. Passing through a pressure-reducing device prepares it to absorb energy again. Refrigerant remains separate from the drinking water.

Consider an invented complete cycle that takes 2 kilojoules from the air and receives 1 kilojoule of electrical work. With no net energy stored in the heat pump over that cycle, it delivers 3 kilojoules to water. The heating coefficient of performance, or COP, is heat delivered divided by work supplied: 3 ÷ 1 = 3. This ratio exceeds one because the numerator includes energy taken from the air.

Removing energy also cools the surrounding air. If a building’s heating system must replace that energy, its input matters to the wider account. Actual performance depends on conditions, and hybrid models may also use resistance elements. The small energy budget explains the principle, rather than promising a particular product’s performance.