The general layout of the appliance is similar to a conventional electric water heater, but there are some installation considerations. The integrated heat pump makes the tank a little taller than standard tank water heaters, and they require a condensate drain connection.
The biggest consideration, however, is that heat-pump water heaters require a whopping 1,000 cubic feet of ambient air to operate. Also, because the heat pump borrows heat from the surrounding air, homes in colder climates may require the unit to be installed in a conditioned space, and as a result, may not save as much energy. Basically, homeowners would be paying for another appliance to replace the heat being used by the heat pump—a fact that isn’t taken into consideration in efficiency ratings. At the same time, this means the unit may actually help the AC during warmer months.
Fueling Options
Generally, heat pumps are the most efficient tank-type choice for homes that don’t have access to natural gas. However, builders can still earn one LEED point or one NGBS point by installing a high-efficiency electric tank model. This includes 80-gallon units rated at 0.89 EF or higher, 50-gallon units at 0.92 EF or higher, or 40-gallon units at 0.93 EF or higher. Electric tank models are not covered under Energy Star, so check efficiency ratings closely. Builders may want to look for an electric water heater that has been certified by the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) to ensure that the manufacturer’s high-efficiency claims are valid.
For areas where natural gas is more cost effective than electricity, builders may want to consider using a gas condensing tank-style water heater. Residential models are still in development, but some manufacturers have been marketing their commercial units for residential use, with some condensing models claiming thermal efficiencies of up to 96%—higher than even tankless, which are rated at about 80% thermal efficiency.
The general operating principles of a condensing model are similar to a standard tank water heater, but with better heat exchange. Instead of venting combustion gases outside like a standard gas tank water heater, a condensing model uses those gases to heat the water. The flue in these models also has been redesigned with a greater surface area so that the heat and combustion gases have a longer distance to travel, and, therefore, heat the water more efficiently. Basically, the tank heats up almost as quickly as it’s filled and can provide more continuous hot water, overcoming one of the usage drawbacks of conventional storage water heaters.
Like condensing furnaces, condensing water heaters produce condensation as a by-product of the combustion process, which means builders will need to install a condensation drain. Also, they require electricity and PVC pipe to accommodate the power venting.