Heat pumps are most often thought of as heating and cooling systems, but they can also be used to heat water — either as stand-alone water heating systems, or as combination water heating and space conditioning systems. Heat pump water heaters typically have a higher initial purchase price than conventional units, but with their lower operating costs, they can start paying for themselves quickly.
How they work
Heat pumps work like a refrigerator in reverse. While a refrigerator pulls heat from inside the box and into the surrounding room, a heat pump water heater takes heat from the surrounding air and dumps it (at a higher temperature) into a tank to heat water.
You can purchase a stand-alone unit or install a system that combines heating, cooling and water heating. These combination systems pull their heat indoors from the outdoor air in the winter and from the indoor air in the summer. Because they remove heat from the air, any type of air-source heat pump system works more efficiently in a warm climate.
Energy efficiency and operating cost
The efficiency of a water heater is measured by uniform energy factor (UEF), which measures the amount of hot water you get compared to the amount of power or fuel used. The higher the uniform energy factor the more efficient the water heater. Heat pump water heaters have a much higher uniform energy factor than conventional units; a typical heat pump unit has a UEF of 2.75, compared to 0.70 for a high-efficiency gas storage system.
It's important to remember that a higher energy factor does not always mean lower operating costs. When looking at heat pump water heaters, consider the size of the unit, your water heating needs and energy prices.
If you choose to install a heat pump water heater, purchase an ENERGY STAR®-certified unit. ENERGY STAR water heaters are more efficient than standard units.