Gas Furnace Components: The Exhaust Flue

Posted by Chris Allen

Gas furnaces have remained the most common type of heater found in U.S. homes for almost a century. One of the reasons is their superior heating power and low cost of operation. Compared to most electric heaters, like electric furnaces and boilers, gas furnaces do not cost as much to run because of the lower price of natural gas. Although heat pumps have greater energy efficiency than gas furnaces, they can sometimes struggle with low temperatures, a problem gas furnaces don’t have.

To help you have a better understanding of gas furnace operation, we’re going to look at one of their most important components: the exhaust flue. When you need repairs or maintenance for your gas furnace in Charlotte, NC, call us at Air Conditioning Experts, Inc.

The Exhaust Flue

A gas furnace creates heat through the gas jets along a burner unit. The heat from this gas then transfers to the air through the heat exchanger, a metal chamber that glows hot from the combustion gas that enters it. The blower fan sends air across the heat exchangers and then into the ductwork.

This process leaves behind combustion exhaust in the heat exchangers, made of toxic carbon monoxide and carbon dioxide gases. To safely keep this from entering the home, it vents out the exhaust flue, a pipe, usually made of sheet metal, that leaves the furnace cabinet vertically. The exhaust flue pipe is specially sized during installation to handle efficiently the amount of exhaust the furnace produces.

In older furnaces, the exhaust flue rises up directly to the roof to expel its exhaust gases. In more modern furnaces, specifically high-efficiency condensing furnaces, the flue can be made of PVC piping that can leave either horizontally or vertically from the furnace and runs beside another PVC pipe that brings in fresh air to the furnace.

Caring For Your Gas Flue

It’s important that the gas flue contain no obstructions and allows a free flow of exhaust gas out of the furnace. Even if a partially blocked flue isn’t forcing exhaust fumes out the furnace and into a home, improper venting will lower efficiency and lead to a reaction between the exhaust gases and the heat exchanger that can cause corrosion and cracks along the exchanger. Cracked heat exchangers must be replaced or they can lead to carbon monoxide leaking.

To prevent this sort of damage from happening to your furnace, make sure you have regularly scheduled maintenance every year to check over the flue and see that it is clean and unobstructed. You’ll have a more efficient and safer furnace.

Air Conditioning Experts, Inc. offers the Comfort Club to bring you high quality annual maintenance for your gas furnace in Charlotte, NC (and your air conditioner as well). You’ll also receive a 15% discount on repairs. Call us today to start protecting your furnace.

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