Heat Pump Water Heaters

[Jim Katen]

Is it just me, or are these things really stupid? 

Today's new-construction house had an AO Smith heat pump water heater in the garage. When I arrived on site, it was 42 degrees outside and about 39 degrees in the garage. The water heater was set to 120 degrees in the "hybrid" mode and its heat pump compressor was running non-stop while its indicator showed that it was also running one of the resistance heating elements. Even so, the hottest temperature that I could get *at the water heater's outlet pipe* was 110 degrees. By the time it got to the fixtures it was about 102 degrees. Even when I switched it over to pure resistance heating and checked back a few hours later, the best it could do was 114 degrees at the outlet pipe.

Most of the ones that I see are set to 130 or 135 in order to get 120-degree water at the fixtures. In our climate, these are always installed in a garage because otherwise they'd be fighting with the heating system in the house. In the winter, the garage is always going to be close to 40 degrees and the heat pumps generally stop working and switch to resistance heat at 37 degrees. 

So are these just really stupid or am I missing something? 

[Bill Kibbel]

On 10/26/2024 at 1:30 AM, Jim Katen said:

Is it just me, or are these things really stupid? 

When these first started to appear, I had the chance to discuss them with someone involved in the development and initial trials.  At that time, all data (efficiency, sizing guides etc.) were based on these systems having a continuous flow of air at just over 67° supplied to the intake.  They're all installed in basements here, without any ducting of exterior air - regardless of the manufacturers' recommendation.