What Are the Causes of Flue Pipe Corrosion?

Written by christie gross
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What Are the Causes of Flue Pipe Corrosion?
A blocked water heater flue pipe can cause it to rust. (Jupiterimages/Comstock/Getty Images)

A flue pipe is typically found on gas and electric water heaters. It funnels steam and hot gases outside that the water heater produces during the combustion process as water is heated for home use. A corroded flue pipe usually points to a problem with your water heater and necessitates a call to a plumber to evaluate its performance.

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Poor Venting

A properly functioning flue pipe should disperse exhaust into the open air. However, when not enough draw exists to force exhaust from the pipe, hot, combustible gases and steam begin cooling and collecting on the interior of the flue pipe. Since these exhaust deposits usually contain acid, they deteriorate the flue pipe's metal and cause pipes to corrode over time. According to Water Heater Timer, a flue pipe that is no longer venting properly rusts and creates holes in the pipe that allow toxic gases to enter your home, which causes a dangerous health hazard to occupants.

Missing Cover

Most metal flue pipes have a protective covering that lets gases exit but prevents water and debris from entering the pipe. When the cover is missing or broken, rain and snow can enter the pipe and linger inside. The presence of moisture in the pipe can cause it to deteriorate and corrode. Contact a plumber to inspect your flue pipe and verify the condition and confirm the presence of your pipe cover.


During the combustion process, water is heated at extremely high temperatures, which produces hot gas and steam. The high temperature of the gas and steam exhaust causes it to rise up through the pipe flue in a process called atmospheric draft. Yet when a clothes dryer, exhaust fan or combustible materials, such as gasoline or paint, are placed too close to the pipe flue, they can actually reverse the atmospheric draft and cause a backdraught. A backdraught prevents hot gases and steam from escaping the flue pipe, and, as a result, the exhaust lingers in the pipe and corrodes it. A qualified plumber should be aware of the clearance -- the distance from the flue and appliances and combustible materials -- needed to allow your water heater pipe flue to function properly.

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