Water heaters are pretty simple appliances, especially electric ones. Just start with an insulated tank that has a typical capacity between 30 and 80 gallons. On the top, a cold water line enters the tank, and just eight or ten inches away, a hot water line exits the tank. A temperature and pressure relief valve (T&P valve) is also installed in the top, or high up on one side of the tank. This prevents a dangerous build-up of temperature and pressure in the tank which can cause it to explode.
In electric units, heating elements are installed in the sides that extend into the middle of the tank that is filled with water. These simple resistance elements heat up when electricity runs through them and transfer this energy into the water. Basic dial-type analog thermostats are attached to these elements so the outlet water temperature can be adjusted depending on the user’s preference. If children are in the house, or visit frequently, thermostats should be kept between 120 F and 130 F.
Gas water heaters feature a gas burner on the bottom that heats the water like a range top heats a pot of water. Again, a thermostat allows for temperature regulation. These tanks, however, are a little more complicated because they need a gas line plumbed to the intake gas valve and a vent pipe to carry away combustion gases. In typical installations, this vent pipe connects to the house flue and is exhausted through a chimney.
For houses without a flue, gas heaters with a power vent (that pumps combustion gases to the outside via plastic pipe) are available. These cost quite a bit more than standard gas (or electric) models, but they do make gas an option in flue-less houses. Both types of tanks have a drainage cock on the side near the bottom to drain the tank for servicing and maintenance. A garden hose easily attaches to this valve and carries the water to a floor drain, or outside onto the lawn.
Obviously, there are design differences between tanks, but the real variable that impacts their longevity is the water that goes throughthem. A little less than half the residential water supply in the U.S. comes from ground water (water wells) and slightly more than half comes from surface water (lakes, rivers and reservoirs).
Both sources have sediment that can settle out when the water enters the water heater. Some are just sand while others are precipitated minerals, like calcium chloride. As this sediment builds in the bottom of the tank, it can reduce the efficiency of the tank because the sediment insulates the heat source from the water (at the bottom of the tank for gas heaters) and around the heating elements (on electric models). Over time the accumulation of sediment can corrode the inside of the tank, eventually causing leaks that require tank replacement.
Flushing out sediment
A yearly draining of the tank will eliminate most build-up. Here’s a simple step-by-step program:
Because the amount of sediment in the tank is primarily a function of the condition of the water being heated, it’s important to pay attention to how much sediment is being flushed out. The more sediment, the more frequently you should drain the tank. The less sediment that accumulates between flushings, the longer the tank will last. Also, keep in mind that the best time to drain a tank is after you’ve been away for a few days. If you turn off the tank before you leave and drain it as soon as you get back, you won’t be flushing hot water down the drain or out on the lawn.