Heat Pump Water Heaters

Source: NRECA; RESNET

A major consumer of electricity in today's home is the water heater. Because of how electric water heaters work, using electric resistance elements, these units max out in efficiency at about 96 percent. As the government and industry seek ways to reduce energy use and the resulting carbon emissions, they have turned their attention to the electric water heater. After a lengthy study, the U.S. Department of Energy issued rules governing the efficiency of electric water heaters that went into effect in 2015. The rules resulted in a jump in efficiency requirements for larger residential electric water heaters. Enter the heat pump water heater (HPWH).

PROS
OF HEAT PUMP WATER HEATERS (HPWH)

CONS
OF HEAT PUMPWATER HEATERS (HPWH)
  • Efficiency can be as much as 2.5 times higher than an electric resistance alternative
  • Cools surrounding space in the summer, making the area more comfortable
  • Uses waste heat from the central furnace during winter months
  • May qualify for $300 Federal Tax Credit in 2016
  • Can save $330 annually for a family of four, depending on water use and electricity rates
  • Cost about twice as much as electric resistance water heaters
  • The compressor will make a noticeable noise. Insulating the mechanical room can reduce the sound, but doing so reduces the amount of warm air for the unit's use
  • Makes the heating system work harder during winter months because it generates cold air while operating
  • Physical size of a HPWH can be greater than a electric resistance alternative
  • Requires additional space for air flow (1,000 cubic feet) and a condensation drain or pump
  • Slow recovery may be a problem when demand for water is high
  • Heat pumps have been in use for general home heating and cooling since their invention in the 1940s by Robert C. Webber. When the oil embargo of the 1970s brought the need for improved efficiency to the forefront, heat pumps became an important source of increased energy efficiency in the heating, ventilating and air conditioning (HVAC) arena. Heat pumps operate by using compressors, refrigerant, heat exchangers and the difference in outside air temperature versus indoor temps to produce heating and cooling for homes and businesses. These units historically have been most successful in areas with moderate winter temperatures, although advances in technology are making use in colder climates more feasible.

    So, how does a HPWH function and what are its advantages and disadvantages? In short, the HPWH absorbs heat from the surrounding air using it to heat water within the tank. Because the HPWH uses heat pump technology, it can be up to 2.5 times more efficient than a traditional resistance electric water heater. This means it will cost you less to produce hot water for your home and reduce carbon emissions.

    The tables detail the key advantages and disadvantages of the HPWH. As with heat pumps for general space conditioning, the HPWH will provide greater yearround savings in moderate climates. Like any new application of a technology, the HPWH will benefit from steady improvements over time. They are undeniably more efficient than electric resistance water heaters and will pay for themselves in a reasonable amount of time (2-3 years or so). However, they may not be the right choice in every situation and climate. If your water heater is over 10 years old, you should be looking at a replacement anyway to avoid the risk of water damage should the tank fail. Take the time to weigh the pros and cons of the HPWH as a replacement and, if it is right for you, it is a choice that will pay dividends on your budget and in contributing to a reduction in carbon emissions.
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