Fuel-Fired Water Heaters

The heating surfaces for gas and oil-fired water heaters are near the bottom of the tank. Air enters the combustion chamber, combines with the fuel, and the mixture is ignited. Heat is then transferred to the water through metal surfaces at the bottom of the tank.

The vent pipe, an exhaust pipe which carries the by-products of combustion to the outside, also serves as a heat exchanger. This pipe is usually surrounded by the water containment tank, and often contains baffles to slow the escape of these gases through the vent, thus allowing more time for heat to be transferred to the water around the pipe. Thermostatic controls regulating the temperature of the water are usually located near the mid-section of gas and oil-fired water heater tanks.

The proper mixture of additional air with combustion or exhaust gasses is important in gas and oil-fired water heaters, to assist in the safe passage of combustion products to the outside. If their escape is impeded or blocked, serious problems can develop. To assure this proper mixture, gas-fired water heaters are equipped with a cone-shaped draft hood on the vent pipe, as it emerges from the tank.

Oil-fired water heaters are usually furnished with draft regulators attached to the vent pipe, between the tank and chimney. This is a hinged metal flap with a counterweight, to allow for variations in flue gas pressure.

Some gas or oil-fired water heaters may also be equipped with vent dampers on the vent pipe. This energy-saving device automatically closes the vent pipe to prevent the escape of heat to the flue when the main burner is not being fired. This, in turn, slows down the rate at which the water tank cools down.