HPWH Installation Best Practices


It is important to make sure the
pipe insulation is continuous.

Installing a heat pump water heater (HPWH) is essentially the same as installing an electric resistance water heater, so additional trades are not always needed on site. The installer flow chart in the November/December 2022 issue of Mechanical Business (p44, mechanicalbusiness.com) outlines particular instances when additional trades might be necessary, for example, if panel upgrades are required.

Installation is simple, with no refrigerant handling required. In addition to following the guidance of product manuals, consider the following best practices:



  • Follow manufacturer specifications regarding water heater clearance and seismic strapping.
  • Position the unit so the control panel is facing outward and easily accessible to the homeowner. Make sure all data connection ports are accessible.
  • Direct exhaust away from any thermostats if present or within 10 feet.
  • Ensure the intake air path is sufficiently free and open.
  • Make sure that the positioning allows for easy access to inspect the water heater and controls, service the air filter, and drain the tank.



HPWHs produce a benign condensate that must be drained away from the water heater. Unlike condensing gas water heaters, which produce acidic condensate as a combustion byproduct, there are no special piping or handling requirements for HPWHs other than to convey the benign condensate to a drain. Ensure the water heater is level so condensate properly collects into, and drains from, the condensate collection pan. Do not drain water into safety water pan under the heater as some HPWHs have leak detection sensors embedded in the bottom of the heater’s housing.

For additional benefit to the homeowner, install the condensate drain with a p-trap and a tee port opening so the homeowner can periodically flush the condensate line with vinegar or similar cleaning solution. Condensate pumps, commonly paired with air conditioners, can be used to drain the condensate produced by a HPWH. A single pump may often be used for both the air conditioner and the HPWH.



If installing on a floor susceptible to water damage, install a drain pan to guard against any problems from future leaks. Connect the outlet from the pan to suitable drainage in accordance with your local code. Electric storage water heaters, including HPWHs, do not need to be raised off the floor with a stand. Most electric HPWHs are taller than electric storage water heaters. Keep in mind they have a larger tank size, and their connections are in different places. Make sure there is space above and around the heater to accommodate the variations for the models you are considering.



To improve the system performance overall, insulate all the hot water piping. It is more important to make sure the pipe insulation is continuous than it is to increase the wall thickness or R-value of the pipe insulation. Follow manufacturer’s instructions but as an example, some jurisdictions require one inch of pipe insulation. This includes R-7.7 insulation for the first five feet of cold pipes from the storage tank, all hot water piping between ¾ to 1 in., and hot water piping less than 3/4 in. if it is: associated with the hot water recirculation system; buried below grade; or travelling from storage tank to kitchen fixtures or to another storage tank. Exceptions apply, including in alterations where unexposed piping does not need to be insulated.

Unfired tanks are required to be insulated. Most HPWHs have internal insulated tanks. A label on the exterior of the tank will show the R-value, which must meet National Energy Code of Canada for Buildings (NECB) requirements for internal insulation in an unfired tank. Provide a minimum R-10 foam pad under the HPWH to minimize unnecessary heat loss through the bottom of the water heater. This is a best practice regardless of floor type.



Do not use a continuously operated circulation pump. If pipe runs to fixtures are too long, use an on demand, sensor, or occupant-activated pump to circulate just enough

As with other water heaters, local code may require seismic strapping. When installing, use rubber standoffs when attaching straps to the wall to minimize the vibration and transfer of sound to the rest of the house.

water to prime the loop with hot water. Connect the return pipe of the circulation loop to the cold inlet of the water heater − this will guide the cooler returning water to pool at the bottom of the tank so it does not interfere with hot water availability. Continuous circulation is particularly detrimental to HPWHs. It will result in a lack of hot water availability and greatly increase energy use. Consequently, never set the circulation system controls to continuous, and advise the homeowner of this requirement. An external thermostatic mixing valve is recommended to increase the storage heat capability of the water heater.



The default for most HPWHs is hybrid operation mode with the supplemental heating elements enabled. Some manufacturers refer to this as “Energy Saver” mode, though switching to the efficiency/economy mode may actually save more. The hybrid mode automatically switches to standard electric resistance heat during periods of high hot water demand. However, most consumers can meet demand and maximize cost savings by using the heat pump mode only. Controls make it easy to switch options during times of high-water demand. Consult the manufacturer manual. Some units even have a vacation mode or timer to help save energy when homeowners are away from home by putting the unit to “sleep.”



Follow the manufacturer’s recommended
service requirements.

After installation, HPWHs require modest servicing. The air filter should be cleaned every six to 12 months, with more frequent cleaning in high dust locations. The heat pumps in current water heaters are designed like refrigerators to operate as a fully-sealed system with no other servicing, so there are no ports to add or remove refrigerant. Like any other water heater, follow the manufacturer’s recommended service requirements including regular maintenance for draining the tank and servicing the anode rod.

With thanks to our sponsors