The standard water heater comes in two flavors: electric and fuel-fired. In the latter, the fuel most commonly used is gas, either natural or propane, but oil-fired heaters are popular in many areas. Fuel-fired units have a vent pipe at the top to carry away exhaust gases. Electric models, on the other hand, simply have a power cable that connects the heater to your electric service panel.
The job of the tank-type heater is not only to heat the water, but to store it until it's ready to use. Therefore, in addition to the tank's heating system, every tank is equipped with insulation to help keep the water warm between heating cycles.
The typical electric unit is wired to a 220-volt circuit. To heat the water, the current passes through electrical-resistance heating elements�usually two, one at the middle of the tank and one at the bottom.
Power is delivered to each element through a thermostat�a switch that senses the water temperature. When the temperature drops, the switch closes to allow current flow, and it opens when the temperature reaches its preset limit. Thermostats have a dial for setting the maximum water temperature�generally between 130 degrees and 140 degreesF, or as low as about 120 degreesF for increased energy savings and scald protection.
Instead of electrical-resistance elements, gas-fired heaters have a burner that's fed gas through a control valve and a thermostat switch. In an oil-fired heater, the burner is similar to that found on an oil-fired furnace. In either case, the burner is usually situated to throw a flame under the tank. The exhaust gases are vented either through a hollow core at the center of the tank or around the tank sides. Because fuel-fired heaters heat the tank, which in turn heats the water, there will be more wear and tear on the tank than with electric heat. A fuel-fired heater, therefore, may have a shorter life expectancy than an electric heater.
Electrical Water Heater
Fuel-Fired Water Heaters