How Does a Gas Furnace Work? A Kansas City Tech Explains

December 18, 2017

furnace troubleshooting

The short answer? Gas burners fire up to heat a set of metal coils (called a “heat exchanger”). Those metal coils then heat air that is pushed into your home via ducts.

But, like we mentioned, that’s the super short version.

To get a better idea of how your gas furnace works (and, hopefully, to help you troubleshoot furnace problems) read on. We’ll explain the specific steps in the furnace process that allow it to create heat and warm your home.

Need a professional to help you troubleshoot your furnace issues? Just contact us.

Step 1: Your thermostat “calls” for heat

Just like the brain controls the human body, the thermostat controls the furnace. 

You see, the thermostat’s main job is to monitor your home’s temperature. As soon as the temperature inside your house falls below your desired temperature, the thermostat sends a “we need heat” command to the furnace.

For example, let’s say you’ve set the thermostat to 76°. As soon as the thermostat detects that the temperature dropped below 76°, it opens the gas valve connected to the furnace. That valve opens and sends raw, natural gas into your furnace’s “combustion chamber”—a metal box that surrounds your furnace burners (seen below).

Furnace Combustion Chamber 1

Step 2: Gas ignites & air is heated

Gas enters the combustion chamber via multiple gas jets. Depending on the kind of furnace you have, a pilot light (on older furnaces) or a hot surface ignitor ignites the gas jets.

Once ignited, the jets play on a “heat exchanger”. Your furnace heat exchanger is a set of coils or metal that loops in and out of the airflow inside the furnace. Put simply, the heat exchanger is the part of your furnace that actually heats the air.

Furnace Heat Exchanger

So, once the heat exchanger reaches a certain (very hot) temperature, your furnace’s blower motor kicks on and sucks air into your furnace. That air is heated as it moves across the heat exchanger surface.

Step 3: Hot air is pushed into the ducts

Once air is heated, it’s ready to be delivered to your home. A blower then pushes that hot air into the air duct system.

Your air ducts are either rectangular or round passageways made of either metal, plastic or fiberglass. Think of your ductwork as the “pathways” that carry air into and away from your furnace. 

Each individual air duct ends at a “supply vent”— the grated, rectangular piece of metal that blows out warm air.

supply vent on ceiling

A supply vent.

Step 4: Thermostat ends the call for heat

Once the home reaches your desired temperature, the thermostat shuts off the gas valve that feeds your furnace. From there, the furnace components shut off until the next heating cycle.

Have a specific furnace question? Ask your Kansas tech

Having furnace issues and need professional furnace repair? Just contact us.

We’ll come by to inspect your furnace and repair it in no time.


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