1 Power supply
2 Insulated hot water outlet
3 Insulated cold water outlet
4 Temperature and pressure relief valve
5 Control panel and thermostat
6 Heating Elements
|Minimum Efficiency Recommended
|Maximum Efficiency Available
|Approximate Cost to Install
An electric-resistance water heater has electric heating elements submerged in a storage tank. These heaters are easy to install, have no special venting requirements, and require no supply air. They don't require gas lines, and they last longer than fossil-fueled tanks. Some electric-resistance heaters even come with plastic, plastic-lined, or cement-lined tanks, which eliminate corrosion. By doing away with the sacrificial anode, plastic tanks improve water quality in locations where the anode reacts with the water to produce unpleasant smells.
However, electric resistance is usually the most expensive way to heat water. In most parts of the country, electricity costs more per unit of delivered heat than gas or other fossil fuels, and electric resistance provides less than half the hot water per unit of energy than heat pumps provide. Electric resistance elements also require a large power supply.
Timers to turn off electric-resistance heaters can be useful if you use most of the water in the tank just before or just after the timer turns the heater off, or if your utility offers special time-of-day rates. Otherwise, they are only marginally helpful.
Because they cost a lot to use, electric-resistance water heaters are a good choice only if you don't use much hot water, if electric rates are low, or if there is no other option. If you buy an electric-resistance water heater, be sure it is very well insulated.
Courtesy of DOE