Heating Process

Gas fired, forced air heating systems use a fuel source that is kept under constant low pressure being fed to a burner. There is a blower that forces air through the heat exchanger, to the ductwork, then to the heat registers located throughout the structure. The type of burner is either an electric spark, a pilot light or a hot surface.

Thermostats regulate the activity of the various burners through the gas valve that is controlled by a solenoid. This same thermostat also controls the combustion air blower which will force air into the combustion chamber upon demand.

Pilot light systems are regulated by a safety valve that is, in turn controlled by a thermocouple. This is a safety feature designed to turn the flow of gas off should the pilot go out.

As heat is generated in the combustion chamber, this heat is conducted through the wall and into the surrounding air. The hot air rises and as it does, it begins to heat the top of the unit called the bonnet. Inside this bonnet is a fan control that will be activated when temperatures reach the point called for by the thermostat.

Forced Air

A heating system that uses forced air is one in which air is heated and then forced throughout the system. The system is heavily reliant upon the efficient calculation of duct work, placement and size of vents, and the adequate size of the fan to propel the current of air.

The air handler is also important because it contains an air filter, a heat exchanger and controls. The air filter density, thickness, and material from which it is made can impact the flow of air and must be calculated based on the manufacturers specifications and the quality of the indoor air quality to be achieved.


The type of thermostat chosen to operate a forced air heating system can also impact productivity and levels of financial expenditure for the year. Energy efficient thermostats are available today that are recommended by manufacturers of forced air heating systems.

It must be determined if your system is single or multi-stage. The most common is single-stage. Further, it must be determined if a mechanical, digital, or programmable thermostat is needed. These can all be recommended by manufacturers manuals or your local HVAC provider.


Efficiency and Safety

Gas fired forced air heating comes with its own set of inherent efficiency and safety issues. This type of heating loses energy simply because of the type of combustion taking place with the use of a fuel. Some systems counter-balance this loss with the inclusion of a condensing furnace that condense water vapor to preheat the incoming air. This can increase the efficiency of the system in place. Another advantage to using a secondary condensing furnace is the exhaust flue can be made of plastic and smaller in dimension as the exhaust air is less dense and cooler.

With respect to safety issues, heat exchangers in this kind of system may deteriorate over time or be damaged by corrosion. As this happens, carbon monoxide may be released into the living spaces being heated. Detection devices are therefore, recommended.