How Does a Natural Gas Heating System Work?

How Does a Natural Gas Heating System Work?

Know the components of forced-air and water-heating natural gas heaters

By Brad Painting

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The ultimate function of any natural gas heating system is the transformation of the chemical energy of natural gas into heat. Natural gas is a popular fuel source for both commercial and residential buildings due to its cost-effectiveness and comparatively benign environmental impact. Natural gas systems vary according to methods of combustion and heat distribution.


The main types of natural gas heating systems include forced-air and water-heating. A forced-air system uses a furnace to burn the gas, creating heat, which is transferred into a stream of air and distributed via ductwork and supply vents. A water-heating system uses a boiler to burn fuel and transfer its heat into a water circuit that runs below floors and sometimes behind wall and ceiling tiles.

Combustion Process

A pipeline carries natural gas from a central supply to the burner. The burner consists of valves for modulating the delivery of air and natural gas to a flame. The burner must have the proper ratio of oxygen to natural gas or else it will lower the system's efficiency and possibly leak carbon monoxide to the indoors. After the natural gas is burned to create a hot gas, it flows through a heat exchanger to transfer its heat to either an air or water stream, depending on the type of system. These combustion products are harmful to breathe, so they are guided through a flue to the outdoors.

Distribution Process

In a water-heating, or "hydronic" system, a small pump circulates water through a closed loop that zig-zags throughout the building, heating base boards, radiators or wall and ceiling tiles. These targeted mediums store and radiate heat via infrared radiation and convection. This route starts and ends at the boiler, through which the water passes to acquire more heat. A forced-air system uses a similar route, but rather than pumping water, it blows air through ducts connected to supply vents. The warm air mixes with the colder air of the building's interior, and is then suctioned back into return vents to repeat the process.

Temperature Control

The thermostat measures the room temperature using mercury or expanding metals that automatically connect a circuit to turn the heater on when needed. Unlike some commercial heating systems, most residential gas heating systems have only "on" and "off" settings, meaning that the system runs just as hard to achieve a 1-degree temperature increase as it does for a 10-degree increase. For this reason it is important to have a correctly sized heating system that does not excessively cycle between on and off states, which wastes energy and shortens equipment life span.


All furnaces and boilers come with an efficiency rating known as the Annual Fuel Utilization Efficiency, abbreviated AFUE, representing the proportion of a fuel's potential energy that it is expected to extract in a typical season. The design of ductwork or piping also affects how easily air or water can move through the building, and therefore the required amount of fan or pump power. Strategic placement of vents and radiant surfaces can also contribute to more even and efficient heating of a living space.

About the Author

Brad Painting is a regular contributor to DexKnows and specializes in green building design.

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