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Inspecting Heat Pump Water Heaters

With the new hot water tank requirements, we will be seeing more heat pump type hot water tanks. We will look at how they work, then how to inspect them. First some background. Heat Pump Water Heaters (HPWH) have been around for quite some time. Earlier units were not integrated. They were add-ons to existing conventional hot water tanks. They look like a large cube, next to a hot water tank. A heat pump would pump water from a tank water heater, heat it and then return it to the tank. The modern units are integrated into a single unit. A heat pump basically moves heat from one place to another, no different than a conventional air conditioning unit. A HPWH moves heat from your basement or mechanical room into the hot water tank. This may also reduce humidity and lower the temperature in the area where the unit is installed. Auxiliary electric heating elements are installed to compensate for large hot water demands. Most HPWH can normally heat 8 gallons of water per hour. In comparison, a conventional electric unit can heat 20 gallons per hour. Most HPWH have different modes;

  • “Hybrid” – uses both electric heating elements and the heat pump. This is the recommended setting and likely the default setting on many units.
  • “Heat Pump” – uses only heat pump. Not a recommended setting as the hot water recovery time is considerably diminished.
  • “Full Electric” – works as a conventional electric hot water tank

Typical Control Panel

What should a home inspector be looking for MORE…

Inspecting Heat Pump Water Heaters  

  • Ambient air where the tank is installed should be between 45°F and 100°F. If the temperature drops below 45°F, the unit will switch to full electric mode
  • Ambient air in the area where the HPWH is installed will be reduced by 2-4°F
  • It is recommended HPWH are installed in areas where the temperature is between 50-55°F. The unit becomes less efficient as the temperature decreases.
  • HPWH’s should be installed in areas with a minimum volume of 750 cubic feet (room size -10’ x 10’ x 7’6” high) for 55 gallon tanks, 1000 cubic feet for 80 gallon tanks
  • The expected serviceability life is generally the same as conventional tanks
  • Clearance requirements are as follows: Front – 2’, Rear- 8”, Top – 16”
  • The air entry and discharge at the top of the tank must be free of obstruction to allow air to flow freely
  • The unit should not be installed in obstructed air space
  • The air filter, usually at the top of the unit, should be clean. There may be a screw securing the filter panel to the unit
  • The evaporator coils should be clean and undamaged
  • If installed in the living space, it may reduce the temperature, causing the heating system to activate more often
  • It should not be installed near a thermostat
  • The unit will be much more noisy that a conventional electric unit, similar to a window air conditioner
  • HPWH’s should not be installed in a kitchen; oils can damage the unit
  • The condensate drain line should be undamaged, and delivered to a proper drain. The use of a condensate pump may be required
  • It is recommended that the electric supply for the condensate pump is directly from the unit, not from a separate GFCI receptacle. This is to ensure that water does not accumulate around the unit if the GFCI trips
  • It is recommended that a HPWH is slightly elevated and installed in a catch pan
  • Any water in the catch pan or around the unit indicates a leak or damaged condensate drain
  • The 240V electrical connection should be inspected. Most units require 10 AWG with a 30 Amp double pole dedicated circuit breaker
  • Temperature and Pressure relief valve should be installed with an adequate discharge pipe to within 6” of the floor
  • A shut off valve should be installed on the cold water inlet pipe
  • A thermal expansion tank should be installed
  • The tank temperature should be set at 120°F

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