A smiling technician with arms crossed standing between a conventional and a heat pump water heater

Heat pump water heating is a technology that has gained traction recently. As a homeowner, you may be familiar with the term or even how heat pump water heaters function. 

However, you may be uncertain about the considerations for installing one.

Where you install a heat pump water heater (and its accompanying implements) determines whether you need any modifications. Read on to learn how to install a hybrid water heater.

Disclaimer: Always, always read your specific model number’s instructions 100% of the way through, and ideally a few times.

How To Install a Heat Pump Water Heater

The process of installing a heat pump (hybrid) water heater depends on its type. For example, a hybrid electric model requires a 240V circuit, while a plug-in heat pump water heater runs on 120V. Also, heat pumps have a few extra installation requirements vs. conventional water heaters.

To install a heat pump water heater, ensure that minimum clearance and space requirements are met. A heat pump also requires a condensate drain line. In addition, you may have to extend your existing plumbing for the cold inlet and hot outlet and install an air duct. 

1.) Check the Minimum Clearance and Space Requirements

Most heat pumps require some clearance on at least one side. Below is Rheem’s installation manual for their most popular heat pump water heater unit, for use as a reference (you can download it too).

I followed this closely when I installed my own at our latest net-zero renovation home as well:

For instance, Rheem hybrid water heaters need at least two inches (5.08 cm) clearance to the side for the following series:

  • Performance Platinum
  • Performance Prestige
  • Professional Platinum
  • Professional Prestige

Rheem’s ProTerra hybrid water heaters have the same clearance requirement. 

Likewise, if you have an A.O. Smith hybrid water heater, such as one of the Voltex models, the clearance requirement is three inches (7.62 cm) to the side.

In most cases, this side clearance requirement is for components such as the following:

  • Cold water inlet and hot water outlet
  • Condensation line outlet and drain
  • Temperature and pressure relief valve

Additionally, you might want to leave some space behind a heat pump water heater to make the following processes easier:

  • Installation
  • Maintenance
  • Repairs
  • Servicing
a blue tesla model 3 on the left with a rheem hybrid heat pump water heater on the right in a garage
Here is our Rheem heat pump water heater installed in the garage of our latest net-zero solar home renovation.

For standard models with a capacity of 40-80 gallons (approx. 150 to 303 liters), around six inches (15.24 cm) of clearance behind a heat pump water heater should be enough. Of course, you may leave a bit more space, like eight inches (20.32 cm), if you want, or if there are pipes, shut-off valves, etc.

The minimum space requirements shouldn’t be an issue if you set up a heat pump water heater in spaces such as:

  • Basements
  • Garages
  • Large utility areas
  • Ventilated spaces

Also, the available space around your heat pump will impact its efficiency and efficacy. For example, a large room with a lot of stuff blocking air circulation or obstructed ventilation might call for an air duct.

2.) Determine if You’ll Need an Air Duct or a Louvered Door

Here are a few instances when a hybrid water heater doesn’t require an air duct:

  • A.O. Smith Voltex hybrid heat pump water heaters in an enclosed closet, room, space, etc. larger than 450 ft3 (12.7 m3)
Closeup on the top of an A.O. Smith Voltex® Hybrid Electric Heat Pump Water Heater in a basement
Courtesy of Clean Technica
  • Rheem Performance Platinum, ProTerra Hybrid, and a few other models in a room or space larger than 700 ft3 (19.8 m3)
  • Rheem Professional Prestige, ProTerra, and other models without electric resistance heating in a space larger than 1200 ft3 (33.9 m3)

If your water heater closet is smaller than these space requirements, the heat pump requires an air duct or louvered doors. Plus, there should be at least 0.75 inches (1.9 cm) clearance below a non-louvered door if you install only one inlet or outlet duct. 

A louvered door may have one or two sets of angled slats. If a closet door has only one set of louvers, it must be at the same height as the heat pump’s exhaust. Also, the exhaust air should flow straight to the top louvers, and the door must have 0.25 inches (0.6 cm) clearance below.

Small enclosed closets with no clearance under a non-louvered door require an inlet or outlet air duct for a heat pump. Some models may need both inlet and outlet air ducts. If you install an air duct, setting up a heat pump water heater doesn’t have any space requirements whatsoever.

3.) Ensure the Circuit Breaker and Voltage Are Appropriate

Rheem’s plug-in heat pump water heaters require a 120V single-phase AC circuit with a 15A breaker. Some Rheem models can run on a shared circuit, while others need a dedicated one. For example, the Rheem hybrid models require a 240V single-phase AC circuit with a 30A breaker.

On the other hand, A.O. Smith’s hybrid water heaters require a 208/240 VAC 60 Hz single-phase circuit with a 30A power supply. 

For reference again, here’s a copy of A.O. Smith’s Installation Document (most popular model at Lowes):

Check your model’s amperage and voltage requirements to ensure the available wall outlet has the proper circuit with an appropriate breaker.

If you’re replacing an old heater, you should remove it and perform the following checks:

  1. Turn off the circuit breaker to your old heater and check if the terminals have any voltage. Then, use a multimeter or voltmeter at the terminals inside the access panel of the old heater to verify that you have turned off the appropriate circuit breaker.
  2. Close the water supply shut-off valve and drain the old heater tank with a hose or a transfer pump if draining takes a long time. Remove the flexible supply lines from the water heater and move the appliance to make space for the new one.

You’ll also know whether you have the required circuit and breaker at this stage.

4.) Extend Your Plumbing for the Water Heater

Although exceptions exist, conventional gas and electric water heaters usually have supply lines behind or above the tank. Heat pump water heaters typically have these inlets and outlets to the side. Also, the cold water inlet is likely to be at a much lower height than the hot outlet.

two men installing a heat pump water heater in a garage
Installing The A.O. Smith heat pump water heater from Lowe’s in our first net-zero renovation.

You may have to extend the cold and hot water lines using the following:

  • PEX pipes or others
  • T-adapters and elbows
  • Valves, as necessary

If you split the main supply line to feed the cold water fixtures in your house and the heater tank, you should get a shut-off valve for the latter after the diverter or T-adapter so you can close it when you don’t need to use the heat pump. 

Generally, heat pump water heaters have 0.75 inches (1.9 cm) NPT water inlets and outlets for the cold and hot lines. Standard flexible hoses with brass lock nuts should fit these connections. But you must still extend your plumbing to connect the inlet and outlet ports. 

5.) Install Your Water Heater and Fill the Tank

Once the plumbing setup is ready, installing your heat pump water heater is simple. 

All you have to do is follow these steps:

  1. Place the drain pan or foam pad on the floor, depending on what the kit includes.
  2. Mount the heat pump water heater on the insulated platform and align it properly.
  3. Connect the supply lines, inlet, and outlet, and tighten with a spanner or wrench.
  4. Install seismic trapping if it’s required per your local code, like in the Pacific Northwest.
  5. Connect a PEX tube to the temperature and pressure relief valve and tighten it.
  6. Attach the relief valve. It isn’t always factory-installed, but it will be in the kit.
  7. Get a sizable bucket or pan and place it directly under the PEX pipe, just in case. 
  8. Turn on the shut-off valve and fill the tank before connecting the heater to electricity.

As the tank fills up, you can complete step seven and return to step six. 

6.) Open Hot Water Fixtures To Remove the Air in the Tank

Heat pump water heaters shouldn’t be operated if the tank is empty or not entirely full. So, you must remove all the air from the tank. Open a few hot water fixtures in your home. Let cool water flow out through these faucets and other fixtures to purge all the air in the tank.

7.) Run the Condensate Line to a Drain or Use a Pump

All hybrid water heaters have a condensate line you should connect to a drain nearby. This drain may be a typical one that uses gravity. If you don’t have such a drain or the water heater is in your basement, use a condensate pump to eliminate the water resulting from condensation.

A ductless mini-split condensate drain at the bottom of line near the compressor
Courtesy of Quality Heating and Sheet Metal Company, Inc.

Most hybrid water heaters have a condensate outlet toward the rear or a side. Use a 0.75-inch (1.9 cm) NPT hose or pipe to run the condensate line to the drain or a pump. The latter is going to need a power outlet nearby. Small condensate pumps require the typical 120V outlet.

8.) Set Up the Electrical Connection for the Water Heater

Plug-in models are a turnkey electrical setup. You simply plug the power cord into a typical 120V or 240V receptacle, depending on the heat pump water heater model. If a model has wires, connect them to ground, live, and neutral and to an outlet rated for the amps and volts.

Final Thoughts

Use plumber’s tape, aka PTFE or Teflon, for the brass connectors and other locking nuts to prevent water leakage. A heat pump water heater with electric resistance heating elements may be set to hybrid mode. Switch to the heat pump mode for maximum energy efficiency.

The heat pump will have an air filter you should clean every three months or so. Also, you must replace this air filter when necessary. If a hybrid water heater is inefficient in a room due to cold ambient temperatures, move it to a conditioned or warm space.

Best of luck!


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