My experience in replacing electric tank heaters with HPWHs is that customers typically save about 50% on their water-heating costs. Those who have switched from cold-start oil-fired DHW tanks usually experience greater savings.
In Maine, where I live, the average cost of domestic water heating with a conventional tank-style electric water heater is about $50 per month for a household of two or three “moderate” hot water users. Most HPWH users of the same household size end up paying about $20 per month—a 60% savings. Households that switch to HPWHs typically recoup the additional expense within three to five years. If you had also previously operated a dehumidifier, the payback time will be shortened, since the HPWH will also be serving this purpose. Sweetening the payback is a federal tax credit of $300. Some states and utilities also offer rebate and incentive programs for installing an HPWH.
In a two- to three-person household, an HPWH may use 3 to 4 kWh per day, drawing about 700 watts per hour when heating. Paired with large storage tanks that are used for solar (or a wood-fired boiler), an HPWH can serve as effective backup.
The key to affordable operation is a well-insulated storage tank. I use a 350-gallon storage tank (insulated with 4.5 inches of polyiso foam) with my Nyletherm HPWH (an earlier version of the Geyser). During the heating season, this tank is fed by a wood boiler. During the nonheating times of year, the heat pump runs about four hours a day to maintain our hot water at 120°F, avoiding the use of the boiler. When the stored water drops to 116°F, the heat pump comes back on. The operational cost has turned out to be the same as when we used a foam-insulated, 80-gallon commercial storage tank—yet provides much more heated water.
A stand-alone unit such as the Geyser can be tied into any larger tank. Since the Geyser has a built-in bronze circulator pump, it can move water to and from any storage tank up to 50 feet away.
An all-in-one HPWH can also integrate as a backup for larger storage tanks. This requires circulating water between the two tanks, but it is doable. A small bronze circulator pump and an aquastat on the larger tank moves hot water in the HPWH tank to the larger tank when it is cooler.
Of course, the easier way to pair renewable energy with an HPWH is with a solar-electric system, since it can simply provide the electricity used by the HPWH.
Tom Gocze has been a solar thermal installer and manufacturer since 1979. He holds three patents related to solar heating and heat-storage systems. Many of the unpressurized heat storage systems sold today are based on his work.
Energy Star Heat-Pump Water Heater Manufacturers:
A.O. Smith • hotwater.com
AirGenerate • airgenerate.com
American Water Heaters • americanwaterheater.com
General Electric • geappliances.com
Nyle Systems • nyle.com
Reliance Water Heaters • reliancewaterheaters.com
Rheem • rheem.com
Richmond • richmondwaterheaters.com
Ruud • ruud.com
State • statewaterheaters.com
Stiebel Eltron • stiebel-eltron-usa.com
U.S. CraftMaster • uscraftmaster.com
USI Green Energy • usigreenenergy.com
Whirlpool • whirlpool.com