Heat Pump Water Heaters
If you currently have a standard electric water heater and want to cut your water heating energy costs, you might want to consider a heat pump water heater. Heat pump water heaters can be two to three times as efficient as a conventional electric resistance water heater because the electricity is used to move heat from one place to another rather than to generate the heat directly.
How It Works
A heat pump water heater heats water by transferring heat from the surrounding air to the water in the tank. It uses the same refrigerant cycle or vapor compression cycle as a space heating heat pump, alternately evaporating and condensing a refrigerant to absorb heat from one environment and release it to another. This is the same principle used in refrigerators and air conditioners. The difference is that refrigerators and air conditioners are used to remove unwanted heat, while the heat pump water heater captures that heat and puts it to work.
Because the heat pump water heater extracts heat from the surrounding air, it cools the air at the same time. This free cooling can be useful if the unit is located in an area where cooling is desired.
Heat Pump Water Heater Types
There are two types of heat pump water heaters - a retrofit or add-on heat pump to work with your existing water heater, or an integral unit that includes the water storage tank and heat pump all in one. If your existing water heater is relatively new, the retrofit or add-on unit is a good choice.
If your water heater is older and you anticipate replacing it in the near future, an integral unit would be a better option.
Unfortunately, residential heat pump water heaters are not widely available at this time (most are designed for small commercial applications). There are only several units currently on the market. Several manufacturers have discontinued their lines of heat pump water heaters due to lack of consumer and contractor awareness. However, interest has recently been revived with tax credits and other incentives, so availability is expected to increase in the near future.
Swimming Pool and Spa Heaters
Although not widely used at this time for heating domestic water, heat pump water heaters are an excellent option for heating swimming pools. In fact, most electric pool and spa heaters are actually heat pumps. They are typically installed outdoors, next to the pool or spa, and draw their heat from the surrounding air. Manufacturers claim efficiencies as high as 500%. Depending on utility rates, they can be less expensive to operate than natural gas or propane heaters, although their initial cost can be significantly higher. If you're considering adding or replacing a pool or spa heater, check with a reputable supplier for comparisons based on local utility rates.
When purchasing or installing a heat pump water heater, keep the following basic guidelines in mind:
- Follow the manufacturer's guidelines for minimum dimensions of the area in which the unit will be installed. If installed in smaller areas, extra ventilation may be needed.
- Install the unit in an area that won't be adversely affected by the cooling.
- If possible, install the unit near equipment that produces waste heat, such as dryers, boilers, or furnaces.
- Provide a drainage outlet for condensation. During humid weather, the heat pump water heater may produce as much as five pints of condensation every hour.
- Insulate exposed hot water pipes to reduce heat loss.
- For add-on or retrofit units, leave the electric heating elements and thermostats in the storage tank intact. When the heat pump alone can't satisfy the thermostat setting, the electric elements will turn on and make up the difference.