Heat Pump Water Heater Frequently Asked Questions

This is part of an expert best practices web guide to Heat Pump Water Heaters published by the ENERGY STAR Residential New Construction program. Read Part I of the guide.

More Expert Guidance About Your New Heat Pump Water Heater

Where can integrated Heat Pump Water Heaters be installed?

Heat Pump Water Heaters are designed to be used in spaces with ambient temperatures ranging from about 40 to 120 degrees Fahrenheit. This can include garages, basements, laundry rooms, and closets with louvered doors. The warmer the air, the more efficient the operation. HPWHs should always be protected from the elements.

The sound of a Heat Pump Water Heater is similar to that of a dishwasher—between 45 dBA and 55 dBA—which may be noticeable if located near a bedroom. Since Heat Pump Water Heaters will also have a localized cooling effect when the heat pump is running, do not place them in frequently occupied areas with temperature-sensitive activities.

How much airflow do Heat Pump Water Heaters require?

The key to successful Heat Pump Water Heater operation is to provide enough air for the water heater. Nothing needs to be done if the space around the Heat Pump Water Heater meets manufacturer requirements (450 to 700 cubic feet). If installed in a small closet, a full louvered door can be used to circulate air into a larger space. If grilles are used, they should provide a total of 240 square inches of “free air,” which is the space between the fins. Placing a grille at both the top and bottom of a door or closet is the best application. Alternatively, in small closets, ducting can be used for the intake and/or exhaust air from another nearby location.

Can integrated Heat Pump Water Heaters be installed outside?

In cold climate regions where water pipes can freeze, integrated Heat Pump Water Heaters should not be installed outside. If located in a warm climate, a Heat Pump Water Heater may be installed in a carport, garage or an attached outdoor closet provided with properly sized vents or louvers.

Can I use the Heat Pump Water Heater to complement my solar thermal water heating system?

Heat Pump Water Heaters can be used in conjunction with solar thermal. Refer to the manufacturer’s recommendations for installation methods.

What happens to a Heat Pump Water Heater in the event of a power outage?

If the power goes out, a Heat Pump Water Heater will continue to supply the remaining hot water in the storage tank. However, it will no longer heat hot water because neither the heat pump nor the resistance heating element will work without electrical power. When power is restored after the outage, the water heater will automatically revert back to the most recent user settings. In cases where a home is also equipped with batteries and disconnect from the grid, the Heat Pump Water Heater can often continue to run in heat pump-only mode as it draws less than 500W of electricity.

Are Heat Pump Water Heaters loud?

Heat pump water heaters have a fan and compressor, both of which make some noise. When installed in less frequently occupied areas—like garages and basements—most people are unbothered, or even unaware, of the sound. However, noise perception varies between individuals. To reduce the impact of noise, add sound insulation to the space where the water heater is installed or select a quieter model. The ENERGY STAR NextGen program requires that heat pump water heaters in occupiable spaces have sound at levels less than 55 dBA, which is the volume of a background conversation. Even quieter models (rated at 45 dBA and less) are also available.

If installed inside, will the Heat Pump Water Heater's energy savings be offset by extra heating?

Studies have shown that Heat Pump Water Heaters often do not significantly increase heating system runtime when installed in conditioned space because their cooling impacts are small and localized. Interactions are minimized when the Heat Pump Water Heater is installed farther away from the thermostat and air handler, since the cooling from the Heat Pump Water Heater is not mixed with the rest of the home. When a Heat Pump Water Heater is actively heating water in heat pump mode, it generally provides 2,500 to 5,000 Btus/hour of cooling to the surrounding air. With an efficient space-heating system, energy savings from a properly installed Heat Pump Water Heater will exceed any marginal space-heating energy increases, and in the summer, the home will gain some “free” localized cooling and dehumidification as heat is moved from inside the home and put into the Heat Pump Water Heater. Even when there is some interaction, the Heat Pump Water Heater overall provides energy savings compared to less efficient alternatives like gas and electric tank and tankless units. The small impact on heating and cooling is especially beneficial in warm climates.

How reliable are Heat Pump Water Heaters?

Heat Pump Water Heaters have been available for more than 40 years. Current Heat Pump Water Heaters are designed like refrigerators to operate as a fully sealed system. Heat Pump Water Heaters have similar life spans to electric storage water heaters, and many come with 10-year warranties.

Will the occupants have enough hot water?

Heat Pump Water Heaters have hot water delivery capability comparable to (or greater than) electric-resistance tanks. Follow the tank-sizing guidelines on page 8 and review each model’s First Hour Rating. Thermostatic mixing valves can also be installed to allow a higher set point on the water heater and increase the total capacity of the overall domestic hot water system.

When should I go to a bigger tank?

If space, budget, and location allow, a larger tank is typically a better choice. This allows more water to be heated during off-peak times for future hot water use at a later time. A larger tank size will also rely more on the heat pump rather than using the less efficient resistance heating element. The ENERGY STAR NextGen program requires a minimum tank size based on the number of bedrooms.