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Rust and Your Furnace: What You Should Know

Furnace-standardIt’s important to us as HVAC professionals to see that our customers have equipment that operates safely. Whenever we’re called for furnace repair in Durham, NC, we take every precaution to ensure the heating system is fixed so it won’t create health hazards. We also do extensive inspections during maintenance to detect any fault that can lead to combustion dangers or gas leaks.

And one of the main signs we look for in a furnace is rust. Checking for rust is one of the main reasons you want experienced technicians handling regular maintenance on your gas furnace.

How a Furnace Develops Rust and Other Types of Corrosion

If you’re first thought is that a rusting furnace seems strange, it’s probably because you associate rust with water. A furnace doesn’t use water to provide heat; it uses air. Rust is something you would imagine affecting a boiler or water heater.

However, there is some water vapor used in the heating process of a natural gas furnace. This is the water vapor found inside the combustion gas collected inside the heat exchanger. As the combustion gases cool down, some of the gas develops water vapor. In a condensing furnace, a type of high-efficiency furnace, this water vapor goes to a second heat exchanger where it’s condensed to release more heat. In both types of furnaces, there can be some exposure of this water vapor to the metal of the heat exchanger. However, the furnace is designed to vent this vapor out a condensate line and flue.

If a furnace isn’t exhausting gas and condensate correctly—such as because of a clogged or blocked condensate line or flue—there’s a higher chance of a chemical reaction occurring between the combustion gas and the metal, creating corrosion. Long years of exposure to combustion gas can also cause corrosion, so an extremely old furnace is more likely to have rust on the exchanger.

Detecting Rust

You probably won’t see any rust on the outside of your furnace unless you have a water leak from outside that’s coming into contact with the furnace. If you do see any rust on the furnace, call for HVAC technicians right away. Don’t run the furnace until it has received a clean bill of health. The external rust may not be a major problem.

It’s the rust you don’t see that can be dangerous: rust on the heat exchanger. This is one of the many reasons annual maintenance for a gas furnace is vital. HVAC technicians examine the heat exchanger to look for spots of corrosion starting. If rust begins to appear on the exchanger, there is a risk of the exchanger cracking—and that will allow toxic combustion gases to escape into the house. A rusted or cracked heat exchanger must be replaced, and in most cases where the furnace is more than 15 years old, it’s better to have a new furnace installed.

Moral of the story: never forget to schedule annual furnace maintenance, and always call our technicians at the first indication of rust!

Comfort Master Heating & Air Conditioning, Inc. offers quality service throughout the Triangle Area of North Carolina. Schedule service to maintain or repair your furnace today.

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