Heat Pump Water Heater

How It Works

Heat pump water heaters save energy by transferring heat from the surrounding air to the water heater tank. They can be installed to draw heat from indoor air (if cooling is desired) or from outdoor air. Even when the outside air temperature is as low as 40° F, a heat pump water heater can usually extract enough energy to meet water heating needs. It uses the same principle as refrigerators and air conditioners. The difference is that they are used to remove unwanted heat, while the heat pump water heater captures heat and puts it to work.

Waste Cooling

When the heat pump water heater removes heat from the surrounding air, it cools it. Air conditioning energy costs can be reduced by installing ducts to transport "free cooling" to places that need it. A heating and air conditioning contractor can help you evaluate the cost effectiveness of installing the necessary ductwork and controls, and a system for venting the cooled air outdoors during the heating season.

Applicability

The heat pump water heater provides the best energy savings when used in areas where temperatures are mild. When the air temperature drops below 40° F or rises above 100° F, the heat pump water heater may not meet performance demands and will not operate as efficiently. If you provide a back-up heating source (such as a booster heater installed near the point of use) it may be able to meet the demand. However, remember that increased use of back-up water heating may result in lower savings.

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. In general, if the existing water heater is in good condition, the retrofit or add-on unit, is a good choice. If water heater replacement is necessary due to leaks or inoperative heating coils, an integral unit is the optimal solution.

Installation Tips

Follow these guidelines when installing either a retrofit or integral unit:

• Install residential size heat pump water heaters in an area that follows the manufacturer's installation guidelines. If installed in smaller areas, extra ventilation must be provided. Refer to the manufacturer's literature for exact specifications.
• Install the unit in an area that won't be adversely affected by the waste cooling.
• Locate the unit at least 6 inches from surrounding walls.
• 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.
• Install a pressure relief valve and direct the discharge outdoors or into the condensation drain.
• Install dielectric couplings on plumbing connections with dissimilar metals.
• Insulate exposed hot water pipes to reduce heat loss.

When installing a retrofit unit, follow these installation guidelines:

• Install a shut-off valve on each line between the heat pump and the water heater tank.
• Supply back-up heating, if necessary. In a retrofit situation, you can usually leave the electric heating elements and thermostats in the storage tank intact. When the heat pump alone can't satisfy the temperature setting, the electric elements will.
• If back-up heating is unnecessary, disconnect the heating elements.