Water heaters have improved in their efficiency considerably; older water heaters may cost as much as or more to operate than recent furnaces or air conditioners. Three common water heaters include storage tank, on demand, and the newest, heat pump. An Energy Factor (EF) rates their efficiency and applies to all three types. On demand are generally only installed in remote locations where they cannot operate on a storage tank. Heat pump water heaters save considerably in operational costs (1/3 to ½ as expensive), but do not operate well outdoors in cold temperatures. They need sufficient warm air around them and exhausted air is cool and dry (excellent for basements) (Harley, 2012)(Amann et al. 2012).
The consumer product safety commission recommends setting water heater temperatures to 120° F. Using water heater temperatures above 120° F risks scalding and costs 2-5% more for each 10° increase. Lower water temperatures also lengthen the water heater’s lifetime, by reducing scaling and corrosion. However, setting a water heater temperature below 120° F increases the risk of legionella pneumonia (Harley, 2012). To estimate your water temperature, test hot water temperature after an hour of no hot water use, then run water until hot. The thermometer should be able to test to temperatures of 150° or greater.
Adjusting the temperature properly may best be done by a professional. For electrical water heaters, turn off the heat first, then adjust two likely thermostats, one for each heating element at the bottom of the tank (Harley, 2012). For gas water heaters, the thermostat is located by the gas valve; markings must be analyzed and interpreted correctly to adjust.
A heater system’s first-hour rating evaluates how long it takes to turn a cold water tank into a hot water tank, assuming you use hot water up. When buying a new water heater, estimate tank size requirements according to your peak demand hour, considering that a shower is estimated at 20 gallons/person/hour, and a manual dish wash may be 4 gallons/hour (Amann et al., 2012). Installing insulation for the first 10 feet of hot water pipes is recommended. The best way to conserve water is to use efficient low-flow kitchen and bathroom faucets, shower heads, and toilets. (See Optimizing Water Use.)