Heat-Pump Storage Water Heaters
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- Heat pump
- Temperature and pressure relief valve
- Hot water outlet (to taps)
- Back-up electric resistance heating element
- Cold water inlet
- Refrigerant lines
- Hot water storage tank
- Heat exchanger
- Drain pan
|Minimum Efficiency Recommended||2.0 EF|
|Maximum Efficiency Available||2.5 EF|
|Expected Life||11 years|
|Arroximate Cost To Install||$1,000-$1,500|
Heat pump water heaters move heat from the surrounding air into the water. The heat pump is backed up by electric heating elements in the water tank for when demand outruns supply. Heat pump water heaters may be purchased as integral units with their own storage tanks (called one-piece systems), or they may be added on to electric-resistance water heaters. Heat pump water heaters are expensive, but they are a good alternative if electricity is your only available source of energy. They can save 25% to 45% of the cost of heating water with an electric-resistance heater.
In a heat pump, energy is used not to generate heat but to move it, so a heat pump can have an Energy Factor above one. In fact, most heat pumps have EFs between two and three.
When heat pump water heaters move heat into the water, they cool and dehumidify the air surrounding the unit. This produces the equivalent of about 1/2 ton of air conditioning—which is helpful if your home usually needs cooling. But when winter comes, that cool air will put more demand on your heating system.
Heat pump systems should be designed and installed by experts. One-piece systems require less design work and are simpler to install. Choose your contractor carefully.
Heat pump water heaters should be installed inside the house because they can freeze up if the temperature drops below 45°F. And they should be in an open, unconfined space, since they need lots of surrounding air from which to extract heat.
Heat pumps require more maintenance visits than most other systems. Depending on your water quality, the heat exchanger coils may need to be cleaned as often as every three months. This is not something most homeowners can do on their own.
Heat pumps are slow. Most electric-resistance heaters can heat 20 gallons per hour. Heat pumps usually manage only 10 to 15. If demand exceeds supply, the inefficient backup heaters go on. While a larger storage tank can help you to avoid running out of hot water, it will lead to increased standby loss.
Like other storage units, heat pump water heaters are sized by first-hour rating. However, your contractor will also need to size the backup electric coil. Make sure the heat pump is sized to minimize use of the backup system.
Excerpted with permission from No-Regrets Remodeling by Home Energy (1997)