When the cold weather sets in, homeowners depend on their gas furnaces to heat their homes in an efficient and dependable manner. Modern gas furnaces use various electronic components to improve the efficiency and safety of the heating system. In general, they still operate on fairly simple principles.
Older thermostats used a combination of a bimetallic strip and a mercury switch to control the operation of gas furnaces but modern units are almost always digital and use a device called a thermistor. When the temperature falls to a certain level, the thermistor experiences a change in conductivity and triggers the operation of the heating system. Similarly, when the temperature around the thermostat reaches a certain level, the thermistor shuts down the furnace.
The actual heating takes place in a combustion chamber that is sealed from the living space and draws its air supply from a duct system that separately vented to the outside. This configuration is extremely important as the exhaust gases can contain carbon monoxide and are potentially lethal.
The Heat Exchanger
A centrally located, large duct known as the main return is used to draw air from the living areas, into a space inside the furnace called the heat exchanger where the air that will actually enter the living space is heated. When this warmed air reaches a sufficient temperature, the air blower sends it back into the space through another set of ducts.
The blower is simply a large fan with the capacity to move large volumes of air throughout the home. It draws air in, waits for it to be heated and then distributes it throughout the house through a series of ducts.
Gas furnaces may operate on the same principles that inspired their creation in the last half of the 19th century and they may have taken great strides in operational efficiency and safety with the introduction of electronics but they still require proper care and maintenance. So, call a local HVAC contractor to have the maintenance done on your heating system at the beginning of the heating season, properly winterize it at the end and it will provide long years of steady reliable service.