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Corrosion and the Furnace—Yes, It Can Happen

rusted-furnaceWhat sort of home appliance do you think is most likely to corrode? You’ll probably think of the water heater, or shower heads and other water-using fixtures. You probably don’t think about your gas furnace rusting. It doesn’t use water to warm your house, after all. It applies heat to the air through a metal heat exchanger that contains hot combustion gas.

But furnaces can rust, and many do. It can be a minor irritation, a sign the furnace is too old and needs to be replaced, or even a major safety hazard. Let’s look a bit more into how corrosion can affect a furnace and what it means.

How a Furnace Can Corrode

For metal to corrode, it needs two things: oxygen and water. A furnace does have water in it, but it appears in the form of vapor in the combustion gas as it cools down. In a standard furnace with a single combustion chamber, the combustion gas exhaust is sent quickly out a flue, giving the water vapor little time to react with the metal. (This is one of the reasons proper furnace ventilation is important.) In a high-efficiency condensing furnace, the exhaust goes to a second heat exchanger where the water vapor is condensed to remove more heat, and the vapor is then removed through a condensate line. Because of this process, a condensing furnace is at a higher risk of corrosion.

Is This Corrosion Likely to Happen?

Not in a furnace that has regular maintenance from HVAC professionals. Corrosion isn’t common in furnaces under 15 years old unless there is a clogged ventilation flue or condensate drain. A condensate drain can become frozen in winter and increase the chance of corrosion. Maintenance before the winter starts will ensure the furnace is ventilating correctly (exhaust tests are a basic step) and the condensate line is clear.

When a gas furnace is more than 15 years old, the long years of exposure between the heat exchanger and the combustion gas can lead to corrosion. In these cases, it’s best to have a new furnace installed, since the old one is coming to the end of its service life.

The Cracked Heat Exchanger Danger

During maintenance, technicians always inspect the heat exchanger of a furnace to see if there are signs of corrosion. If the metal of the exchanger weakens, it can cause cracks to form, and this can mean the escape of toxic gases into the air of the house. This is a serious concern and one of the few ways a furnace may become dangerous. You won’t be able to see the corrosion or cracks yourself, but rest assured our technicians will locate them. You’ll be able to arrange for furnace repair in Burlington, VT to fix the problem, or in the case of an older furnace, a replacement system.

Exterior Corrosion

You may see corrosion on the outside of the furnace, and this is probably from an external source of water, such as leaks in the ceiling or walls. Shut the furnace off and call us for repairs immediately. We can often fix these problems without needing to replace the furnace.

Call Red Rock Mechanical, LLC for heating service in Burlington and Plattsburgh.

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