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Gas Furnace Parts

Gas furnace keeps you warm on chilly winter nights.
Mukta Gaikwad Mar 12, 2019
The joy of staying indoors, watching the white canvassed world through the frosted windows, sitting by the fireplace, and drinking cups of hot chocolate with marshmallows floating in it is truly indescribable. A sight as such, especially when you are pulling up the driveway after a long hard day at work is so inviting!
If you want to experience the same warm, cozy feeling every winter then now is the time to look up for those gas furnace prices to get the best deal. With several second hand furnaces on sale, you can get yourself a good bargain.
However, used gas furnace may require a bit of maintenance. So, if you are planning to get a mechanic, make sure you know the machine's parts well, to avert any chances of being cheated.
To help you out here is the list of major parts of the gas furnace and a brief description of their functions. The parts might differ from type to type, but the essential (usually common) components are covered here.

Parts of a Gas Furnace

Return Register

This is the basic source of air intake for the furnace. Return register takes in the cold air from the room and is connected to the blower chamber by the return duct.

Return Duct

Connects the return register and the blower chamber. Maintenance of the duct to prevent leaks is very important.


Housed between the blower chamber and the return duct, the main function of the filter is to keep the dust and other particles or elements present in the air, out. These particles may harm the exchanger network and deposition of them may reduce the efficiency, so having a filter in place helps.


Run by the blower motor, this is one of the key parts of the entire furnace system, it helps set up the air draft that is required for the operation of the furnace. The blower's main function is to facilitate the intake of cold air and channel it through to the heat exchanger chamber.

Blower Chamber

Located below the combustion chamber or the heat exchanger chamber (in most of the cases), it houses the blower. It is also the chamber from where the cold air rises to the combustion or heat exchanger chambers.

Gas Control Valve

This is one of the most important control devices of the furnace. It controls the amount of gas being fed to the combustion chamber. It can be an automatically or manually controlled operation. For automatic controls it adjusts to maintain the set temperature.
In manual control if the room gets too warm, the thermostat needs to be adjusted manually to reduce the amount of gas flowing in the combustion chamber, to reduce the degree to which the air is warmed up and fed back to the room. It also works in tandem with the flame sensor, pilot, electronic or hot surface igniter to maintain safe operation of the furnace.

Flame Sensor, Pilot, Electronic or Hot Surface Igniter

This is one of the key components designed for the safety of the furnace. The flame sensors, pilot, electronic or hot surface igniters monitor the presence of the flame in the combustion chamber. If the flame in the combustion chamber goes out, then these sensors stop the flow of gas into the chamber using their link up with the gas control valve.

Combustion Chamber

This forms the part of the heat exchanger unit. The gas fed in the chamber is ignited and combusted to release heat. The combustion chambers are usually long and are snaked to give maximum surface area for heat exchange.
This is a critical component of the furnace and needs to be maintained on a regular basis. Any deposition of dust and dirt on the surface might reduce the efficiency of the furnace.

Heat Exchanger

This component essentially combines the combustion chamber and conduit for forced cool air. The combustion chamber snakes around in the heat exchanger providing maximum area for heat transfer. The cool air is forced from the blower chamber into the heat exchanger for heating it.
The heat exchanger unit is designed to provide maximum surface area for heat transfer between the cool air and the hot, combusted gas. There are usually two sides to a heat exchanger. On the shell side it is cool air and on the tube side it is the hot, combusted gas.
The exchanger unit usually has multiple passes for effective heating of air. The combusted gas will be moved through the tubes several times, because of the layout of the tubes, before being exhausted. This gives us optimum utilization of the heat generated by the combustion of the gas.

Supply Plenum

This essentially is a duct that handles the heated air for supply to the room. It comprises other components like damper, damper handle, etc.

Draft Hood

Connected to the end of the combustion chamber, draft hood facilitates the transfer of hot exhaust gases from the combustion chamber to the exhaust stack. It has to be checked and maintained periodically for effective sealing, otherwise there might be a back draft of exhaust gases into the heat exchanger unit, which may cause a potentially harmful situation.

Exhaust Stack

Exhaust stack connects the heat exchanger unit to the chimney. The main function is to facilitate exhaust of spent combusted gases without letting it leak out anywhere. Regular check up should be undertaken to prevent leakages or to identify the spots from where leaks can occur.


Damper is used to control the draft and prevent back draft. It controls the draft by preventing the air getting heated to be pulled up too quickly. It controls the back draft by preventing the cool air from entering the system through the supply register.
Damper is a critical component for effective functioning of the furnace. It has to be set and maintained at a set angle for its optimum and correct use.

Supply Duct

A supply duct is basically the duct that supplies warm air throughout the house. It can have different outlets and sub-ducts to provide heating to different rooms.

Supply Register

This is the grill through which warm air is fed into the room. Some registers can be shut off, while others may not have that function. It is important that the supply registers are kept clean and unobstructed for effective heating of the room.

Gas Shut Off Valve

This valve can be linked externally with the power switch and the gas source. This valve controls the inflow of the gas to the combustion chamber. In case of signal from the flame sensor, this valve can be triggered to shut off the supply of gas to the system. It forms an important part of the safety as well as control mechanism of the furnace.

Power Switch

This controls the operation of the furnace. Basic switches function to turn the furnace off and on!
Knowing these parts well and how they function will always be beneficial for you. No mechanic who might drop in to repair it in cases of malfunctions would be able to ever trick or cheat you!