Green Plumbing

Answer: B - Heat pump water heaters (HPWHs) work by shifting heat among locations; they do not generate heat specifically for heating water. This renders them unique among water heater types in that the others are all dedicated to water heating. It also increases their energy efficiency by removing the need to actually create heat. However, they are not as feasible as other types of water heaters; they cannot be placed in a location where the temperature falls below about 40⁰ F, and they require a substantial amount of air space around them.