What Is a Hybrid Heat Pump Water Heater?

A hybrid heat pump water heater is an energy-efficient appliance that combines a traditional electric water heater with a heat pump, or at least a single-direction refrigeration circuit. The term “heat pump” is often a misuse of the terminology. There are hybrid electric water heaters that utilize a reverse refrigeration cycle with a reversing valve to manage defrost cycles when installed outdoors, but most systems are designed to be installed indoors or in an area that does not require defrosting.

Unlike conventional water heaters that generate heat directly using electrical resistance elements, hybrid models use refrigeration cycle technology to move heat from the surrounding air into the water tank. This process significantly reduces electricity consumption.

The term “hybrid” refers to the water heater’s ability to operate in multiple modes, allowing it to adapt to different demands and ambient conditions. These systems typically offer both refrigeration cycle and electric resistance heating capabilities, switching between them for optimal performance and efficiency.

Two systems in one unit

Hybrid water heaters contain two integrated systems: the refrigeration cycle and the resistive electrical heating system.

Refrigeration Cycle:

The basic refrigeration cycle starts with the evaporator where we are absorbing heat. The low-pressure vapor refrigerant that has absorbed the heat now moves to the compressor. When the refrigerant enters the compressor’s low side, the compressor will compress the low-pressure vapor into a high-pressure vapor. Once the refrigerant exits the high side of the compressor, it enters the condenser. At the condenser, the vapor refrigerant releases its heat, which causes the refrigerant to condense from vapor to liquid. This is where the water is heated. Heat is transferred from the refrigerant and passed to the water.

Leaving the condenser, the refrigerant liquid is under high pressure and enters the metering device. As the refrigerant moves through the metering device, the high-pressure liquid becomes a low-pressure liquid. Now, once again, entering the evaporator the low-pressure refrigerant liquid absorbs heat and then turns back into a low-pressure vapor. This completes the refrigeration cycle.

Electrical Circuit:

While the refrigeration cycle is the primary heating method, hybrid models also include traditional electric resistance elements. These are used during high-demand periods or when ambient temperatures are too low for heat pump operation alone. The electrical circuit also powers the control board, fan motor, sensors, and safety features.

Typically, a hybrid water heater will require a dedicated 240-volt circuit with a 30-amp breaker. Some models operate on 120 volts and only require a 15-amp or 20-amp breaker. Please check the installation manual to verify the type of circuit needed. A dedicated circuit means a circuit breaker that only services the water heater and no other appliances or outlets. The size of the wiring depends on the size of the electrical circuit. Refer to the manufacturer’s installation manual for specific electrical requirements of your HPWH model. Make sure you follow all local, regional, state, and national ordinances.

Appropriate Installation Locations:

Understanding climate locations is crucial when installing a heat pump water heater. Different climates affect efficiency, performance, and placement. Proper planning ensures the system delivers reliable hot water and maximum energy savings in any environment.

Outdoor Air Sources

In some climates, it is appropriate, or even advantageous, for a HPWH to use outdoor air as its thermal resource. The warmer the makeup air, the more efficiently the HPWH will operate. If outside temperatures are regularly below 50 degrees, it’s best to install the HPWH indoors and use indoor air as the heat source.

Heat Loss to Building

When installing a hybrid water heater indoors, installers must consider the additional load/loss to the HVAC system. As we remove heat from the surrounding air, we must account for the heat transfer in the total load calculation for our building. During the heating season, the refrigeration cycle will remove heat from the surrounding air, causing an increase in the heating load calculation. In the cooling season, the refrigeration circuit will remove heat from the surrounding air, causing a reduction in the cooling load calculation.

Benefits and Limitations

HPWH offers significant energy savings and environmental benefits due to their high efficiency. They are more efficient than traditional water heaters and can save consumers on utility bills. However, they are typically more expensive to purchase and require more space and specific installation considerations. Depending on the manufacturer of the HPWH, some units save up to 60% to 70% on energy costs. Check your area to see if they offer a rebate or tax incentive to help reduce the installation cost. HPWHs typically last longer than traditional water heaters, saving replacement costs. They can dehumidify the space they are installed in, which can be beneficial in some environments.

The space requirements for an HPWH are significantly more than a traditional water heater as it requires air flow. Depending on the manufacturer, this can be between 700 to 900 cubic square feet of air, which is significantly more than a traditional water heater. HPWH can be slightly noisier than standard electric water heaters though not as loud as tankless electric heaters. Electrical upgrades may be needed before the unit is installed depending on the model. A HPWH does require filter changes or cleaning as part of a regular maintenance program.

Decision-Making Guide

There are many factors in selecting the right electric water heater for your household. Consider your household’s hot water needs, number of occupants, bathrooms, and appliances that use hot water. Next, consider the available space and desired tank size. And finally, evaluate energy efficiency and operating costs to make an informed decision.

Let’s break this down.

1. Determine your hot water needs:

Household size: a general rule is to consider 10-15 gallons per person for the tank capacity.

Number of Bathrooms: add 3.5 gallons for each additional bathroom.

Appliances: Add 5 gallons for a dishwasher, and 10 gallons for a washing machine.

2. Water Heater Size and Type:

Tank Capacity: medium-sized water heaters (40 -50 gallons) are suitable for 2-4 people, while larger ones (55+ gallons) are better for larger households. Round up when calculating using method 1 above, for tank size.

Checklist for Buyers and Installers

Look for Energy Star-rated models, which meet strict energy efficiency guidelines.

Check to see if the unit you are buying has any energy rebates that can be applied to reduce its purchase price.

Professional installation is crucial to obtain your full energy efficiency as rated by the equipment you purchase.

Make sure the unit is installed in compliance with all local permits for the city and county.