How Gas Hot Water Tanks Work
by Ed Garcia
In With the Cold
Cold water flows into the insulated steel tank through a vertical pipe known as a dip tube. Tanks normally hold 40 to 60 gallons. A sensor near the top of the tank automatically stops the water flow when the tank is full. In the event that the sensor malfunctions, an overflow valve at the top of the tank will open to prevent pressure inside the tank from exceeding safe levels.
Warming the Water
A circular burner beneath the base of the tank heats up the water based on the thermostat setting (usually between 120 and 180 degrees F). As the water gets hotter, it rises to the top of the tank. Another pipe, or flue, extends from the burner compartment through the roof of the house, venting exhaust fumes. When the hot water tap is off, the tank's insulation helps to keep the water warm. Inevitably, some heat is lost to the surrounding air, and the water will need to be reheated if the tank sits idle for long periods of time. This "standby heat loss" can be reduced by adding insulation around the tank or simply purchasing a more heavily insulated tank.
Out With the Hot
When the hot water tap is turned on, the heated water emerges from the tank and travels through pipes to your shower or sink. If you take a long shower, and the water suddenly turns cold, that means the water heater has fallen behind and has nothing to send you but the cold stuff. If the tank is functioning properly, the hot water will be restored within a few minutes.
Over time, sediment builds up in the base of the tank. To flush the tank, place a bucket under the drain valve and open the valve. Repeat until the water runs clear. The overflow/pressure-release valve should also be inspected once a year by a licensed plumber.