What Is A Gas Furnace?

What Is A Gas Furnace?

A gas furnace provides heat to your home using natural gas. It generates heat quickly and at a relatively lower price than electric heat units. Modern gas furnaces are among the most efficient ways to heat your home with  Annual Fuel Utilization Efficiencies (AFUE) ratings reaching 98.5%.

While there are gas furnaces that burn liquefied petroleum (LP) that consists of propane and butane and others that can use manufactured gas containing methane and ethane, natural gas is the most common.

How Does a Gas Furnace Work?

While it’s the gas furnace that does the work to heat your home, it starts with the thermostat. If you’re having furnace problems, that should be the first place to check. Is your thermostat on, in the heating mode, and set to the proper temperature?

The Thermostat

When you turn your thermostat to Heat and put the temperature above the current indoor temp – or the indoor temperature falls below your preset threshold – it sends a trigger to your furnace that it’s time to turn on.

The Ignition Of The Burner

When your gas furnace receives the signal, a valve is open to let natural gas flow to the burner. It will then ignite the burner in your furnace.

The Heat Exchanger

This, in turn, heats the heat exchanger to warm the air insider the furnace. A motor blower then pushes the warm air into the ducts, which carries the heat to the individual rooms in your house.

Venting The Combustion Waste

A flue takes care of the waste from the gas combustion process and vents it to the outside. If at any time during the process your gas furnace detects a safety issue, it will go into a shut0down sequence to avoid dangerous situations, such as gas leaking into your home.

The Air Filter

Before the air transfers from the ducts into your home, it will pass through an air filter. The filter removes contaminants, such as dust, dander, pollen, and other microorganisms. If your gas furnace doesn’t seem to be operating efficiently, this is another quick place to check. Replacing filters is easy and cheap. They should be replaced according to the manufacturer’s instruction – typically monthly or quarterly depending on the quality of air filter you have.

Warm Air Throughout Your Home

When the warm is blown into your home, it displaces the cooler air which is forced back towards the furnace through your air returns. As the warm air inside your home cools, new streams of warm air will continue to replace it.

Shut Off

When the temperature reaches the temp you sent, the thermostat lets your furnace know it can shut off until the temperature drops below the setting again.



Programmable thermostats provide multiple settings and sequences which may make the process a little more complex but works in a fairly similar manner.