Heat Pump Water Heaters - Cutting Through the Hype

When we purchased our current home, it came equipped with newly installed heat pump water heater (HPWH.) Like many people, I had heard the claims that they were three or four times as efficient as a conventional electric water heater, and on paper that certainly sounds impressive.

One thing I noticed almost immediately was the room cooling effect. The room where our water heater is located serves several purposes, as our house, like many manufactured homes, does not have a dedicated utility room. It also functions as an office, storage room and frequently as a guest bedroom. When hot water is being used regularly that part of the house is noticeably cooler that the rest of the house, fine in summer, but not great the other 9 months of the Maine year. The unit also produces a constant fan and compressor noise whenever it runs in heat pump mode. In a house with a basement or dedicated utility room this might be fine, but in a smaller home, cottage, or manufactured home, the noise can be irritating.

The more I thought about it, the more I began questioning some of the simple efficiency claims often made about these units.

During the summer months, when the house is already warm, I think HPWH make a great deal of sense. They heat water, cool the room, and remove moisture from the air, all desirable features at that time.

The rest of the year things are not so straightforward.

The heat removed from the room is not free. It must ultimately be replaced by whatever is heating the house. In our case that is often wood heat. In another home it may be propane, oil, electric resistance heat, or a heat pump. the economics change depending on the source.

In a house heated primarily with heat pumps or wood, I can see a strong argument for a HPWH, as the replacement heat can be supplied efficiently. In homes heated by propane, oil, electric resistance heat, or inefficient wood stoves, the advantages become less obvious, particularly when comfort, noise, and space requirements are considered. Also, when the higher upfront equipment cost is considered, the likely life expectancy, and the probable yearly energy savings, it may come out as a wash.

I have also come to appreciate the simplicity of propane on-demand water heaters. They are quiet, compact, provide essentially unlimited hot water, and do not create a breeding ground for hydrogen sulphide producing bacteria from iron in well water, which is very common in Maine. Whether they are the right choice for you depends on current fuel prices, usage patterns, water characteristics, and the home itself, but I believe they deserve more consideration in Maine than they sometimes receive.

As with most building products, I have come to believe there is no universally correct answer. A HPWH may be an excellent choice in one home and a poor fit in another. Understanding the tradeoffs is often more important than chasing the highest efficiency rating.