The burner is arguably the most important part of a gas furnace. As gas and air mix inside of it, an ignition system consisting of either a pilot light or electric ignition will ignite this mixture. This will produce heat that’s absorbed by the heat exchanger.
Not all burners are the same, however. While they are all designed to burn a mixture of gas and air, they are available in different types. Most furnaces use either an upshot, inshot or conversion burner.
Upshot burners are designed for use in natural draft furnaces. Natural draft furnaces, of course, rely on natural atmospheric pressure to dispel flue gases. They burn gas and air to produce flue gases. The flue gases are naturally hot, so they will rise into the furnace’s exhaust pipe. Regardless, if you use a natural draft furnace in your home, it will likely feature an upshot burner.
Inshot burners are the most common type. More gas furnaces use an inshot burner than an upshot or conversion burner. They are found in most induced draft furnaces as well as high-efficiency furnaces.
Inshot burners have a valve-controlled gas intake. Gas will enter the inshot burner through the valve. The valve works to control how much gas enters the inshot burner, ensuring that it’s not too much or too little. The gas will then travel to the inshot burner’s tube where it’s mixed with air. The combination of gas and air will then exit out the end of the tube. Upon exiting the inshot burner, the gas and air will be exposed to the ignition system that ignites it.
Conversion burners receive their namesake from their ability to convert the type of fuel a furnace uses. If you have an oil furnace, for instance, you can install a conversion burner so that it will run on gas. You won’t have to replace your entire furnace; you just need to replace the burner. Removing the old burner and replacing it with a new conversion burner will allow your furnace to run on gas.
Conversion burners aren’t as common as upshot or inshot furnaces. They are only used in instances where homeowners want to convert the type of fuel their furnace uses. A conversion burner will “convert” an oil furnace into a gas furnace. If your furnace already runs on gas, you won’t need to use a conversion burner.