We chose a heat pump water heater for our new house, and as I've recently discussed here, there are a lot of reasons why you might be doing the same.
Using an air-source heat pump, heat pump water heaters (HPWHs) extract heat out of the air where they are located to heat the water.
That means that a HPWH cools the space where it is located. That’s a good thing in the summer—it doubles as air conditioning—but in the winter it’s not so helpful. That’s especially the case in a cold climate in a house without a standard heating system.
As we build more energy-efficient houses, particularly when we go to extremes with insulation and air tightness, as with Passive House projects, water heating becomes a larger and larger share of overall energy consumption (see Solar Thermal Hot Water, Heating, and Cooling). In fact, with some of these ultra-efficient homes, annual energy use for water heating now exceeds that for space heating—even in cold climates.
So, it makes increasing sense to focus a lot of attention on water heating. What are the options, and what makes the most sense when we’re trying to create a highly energy-efficient house?