Considerations – Heat Pump Water Heaters (HPWHs)

Basic Considerations

HPWHs are unique compared to other water heaters in that their performance and efficiency are dependent on the conditions in which they are operated.  HPWHs transfer heat from the surrounding air to the water and will produce exhaust air that is cool and dry. In addition, HPWHs generate noise similar to a dehumidifier when running and require periodic air filter cleaning.  HPWHs have unique requirements in terms of placement and available space compared to a conventional electric resistance unit. 

Consequently, before considering a HPWH, you should be able to answer “Yes” to all these questions about HPWH install location.  

HPWH Install Location Questions Check Yes or No
Is location in an unoccupied space where cooling and noise will not be an issue? [ ] Yes [ ] No
Does location offer more than 1,000 cubic feet of surrounding air (i.e., approximately the space of a 12 foot by 12 foot room)?  (Efficiency will suffer in a closet – even one with louvred doors - and you need adequate clearance around air entry and discharge.) [ ] Yes [ ] No
Does location offer sufficient height to install? (HPWH are usually taller than traditional storage tank water heaters to accommodate the heat pump.) [ ] Yes [ ] No
Can location accommodate or does it already have a condensate drain or pump? (HPWHs produce condensate.) [ ] Yes [ ] No
Is ambient air temperature not consistently in freezing range (32 degrees F) or below? (HPWHs do not operate in freezing temperature like outdoors or in garages during northern climate winters.) [ ] Yes [ ] No
Does ambient air temperature remain between 40°- 90° F year-round? (An ideal spot would be near a furnace in a basement that is very warm all winter or a garage in very warm climates.) [ ] Yes [ ] No

Additional Cold Climate Considerations

In colder climates EPA ENERGY STAR suggests you consider two additional issues:

  • In colder climates, most HPWHs are placed in unconditioned or semi-conditioned basements. However, if placed in conditioned space, HPWHs will produce cool and dry air that is a benefit in the summer months but will lead to higher heating bills in the winter months. 2 
  • When operating in heat pump mode, HPWHs do not heat water as quickly as conventional electric resistance water heaters, particularly when recovering after a significant draw.  Consequently, to maintain performance, HPWHs may switch to a less efficient electric resistance heating mode. 3 During these times of recovery, colder ambient air and incoming water will lead to switching to a less efficient electric-resistance mode more often. 

Given these issues, EPA recommends the following for colder climates:

  • Avoid placing HPWHs in conditioned space if possible.  If you must place the unit in conditioned space, do not install it near a thermostat or living spaces sensitive to colder temperatures.
  • Avoid placing HPWHs in garages 4 or outdoors where the temperature can be consistently in the freezing range.   
  • Install HPWHs in unconditioned or semi-conditioned interior spaces, such as a basement, where temperatures remain above 50 degrees F most of the year.  An ideal situation would be near a furnace in a basement that is relatively warm all winter. 
  • Consider HPWHs that meet Northern Climate Efficiency Specification developed by the Northwest Energy Efficiency Alliance (NEEA).  NEEA has identified HPWHs that are efficient in colder climates by using a test procedure that uses lower temperature ambient air and inlet water to reflect conditions in colder climates. A prerequisite to qualify for the Northern Climate HPWH Specification is that the units must be ENERGY STAR certified.  These HPWH units generally have larger compressors that cut off at lower temperatures to work more efficiently in colder climates. Click here to learn more.

2Because the cool air from the HPWH will force your heating system to work harder, paybacks for the HPWHs will be longer in colder climates if installed in conditioned space.  In very warm climates, the benefits to the cooling system working less hard will lead to shorter paybacks.

3 These two heating modes is why sometimes HPWHs are referred to as “hybrids”.

4 In very warm climates, garages can be an ideal place for HPWHs.