Furnaces that work on gas typically have some common gas furnace parts: a gas manifold, gas burners, heat exchanger, vents, ignition controls, safety controls, and blower motor. The appliance itself resembles a large box that absorbs cold air and cleans it by means of an air filter. The air heated by the gas burner is distributed by the blower motor through the ductwork.
The gas manifold connects the main burners with the gas valve. The burners are connected to the manifold via brass fittings, known as spuds. The size of the holes drilled in the fitting depends on the type of fuel used (natural gas or propane) and the amount of gas transported to the gas burners. Most furnaces have spuds for natural gas, but there are spuds for liquid propane as well. In general, the gas manifold requires little maintenance, unless exposed to the elements.
The gas burners are ignited by a pilot flame or electronic ignition that is integrated in most of the modern gas furnaces. The main function of the gas burners is to heat up cold air using heat exchangers that are made of stainless steel. The warm air is then distributed through the ductwork by a blower motor.
The heat exchanger is made of heavy gauge metal mixed with alloys that resist temperatures above 2000° F. Such high temperatures are reached inside the combustion chamber. It is important, therefore, to perform annual inspections and examine the integrity of the heat exchanger. Over time, cracks develop in the heat exchangers and carbon monoxide may leak into the air. Premises with gas furnaces that burn solid or fossil fuels need to be equipped with carbon monoxide detectors. Although heat exchangers are safe, accidents happen and prompt reaction is required.
Vents are usually made of stainless steel or PVC. The latter is used more often due to its lower price and higher durability. The vent pipe carries the exhaust gasses that are formed with combustion out of the premises. The standard venting that is recommended for gas furnaces is type B gas vent pipes.
Modern furnaces use integrated circuit boards to monitor the furnace’s operations. Light emitting diodes show failure codes if the gas furnace is malfunctioning. These codes are typically listed on the door of the furnace and the Owner’s manual.
The thermocouple is a safety control device that shuts off gas in case the ignitor fails or the pilot light goes out. The thermocouple has two metal wires that are placed in a protective case. Upon heating up, the thermocouple sends a signal to the valve by means of a solenoid, which is operated by a volt transformer. The thermocouple converts heat into an electrical signal that allows the valve to close or open.
The blower motor works to distribute warm air through the ductwork, which is then cooled down and returned back to the furnace. Air enters the air filters and a new heating loop begins.