Gas boilers are tanks that sit on top of a burner that is heated by burning natural gas to spread heat into the tank. The tank heats water for hot water and sends it through the pipes to faucets or, depending on the boiler's function, heats water to create steam that is pumped distributed through the house via pipes or radiators.
Boilers in the United States are commonly fueled by natural gas that is distributed to houses via a pipeline located under the road. In rural areas, the boilers may use propane gas that is stored in a large tank outside of the house. The gas is pumped into the house to the burner for the boiler. The burner is lit by a pilot light that generally remains lit. To keep the boiler from overproducing, a temperature gauge and a thermocouple junction are used to regulate the flow of gas from the line to the boiler. The burner heats the boiler, which is a metal tank that generally holds water. A boiler that is used to heat water may also be referred to as a hot water tank. The metal of the boiler heats, causing the water within to heat as well. When the water heats to the desired temperature or evaporates into steam it is distributed throughout the house from the boiler.