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Should There Be Rust on My Furnace?

furnace-oldSimple answer: no. But it can happen, and when it does it means you need furnace service in Woodland Park, CO

Rust and other types of corrosion are almost always bad news for any metal appliance because they weaken the metal. Rust is often an indicator of advanced system age or a failure of another part of the appliance designed to prevent corrosion. These are all true of a natural gas furnace. We’ll go deeper into what this means below. Just please don’t allow rust to stay on your furnace without taking steps to see what’s wrong and what the next step is. 

How Rust Develops on a Furnace

A gas furnace doesn’t use water to run, so how can rust or other kinds of corrosion start in the first place? Isn’t rust the result of water meeting metal?

There are two reasons that rust may begin on a furnace. The first is that there is moisture vapor in the furnace that can lead to corrosion, and it happens inside the heat exchanger. When the hot combustion gases in the heat exchanger cool down after the heating process, what remains is an exhaust vapor that is either sent out of an exhaust flue in a standard furnace or send to a second heat exchanger in an evaporating furnace. If the furnace is venting correctly, the vapor won’t have much chance to affect the metal of the exchanger. After many years, however, the long exposure of the combustion gas with the heat exchanger can begin to have an effect and lead to corrosion.

The second reason is not the fault of the furnace, but of the AC. The common HVAC cabinet setup has the air conditioner positioned above the furnace. If the air conditioner’s condensate pan leaks, it will fall onto the furnace and can lead to corrosion.

Corrosion on a Furnace Is a Serious Problem

The reason corrosion is a major concern for a gas furnace is because it can damage the heat exchanger and allow it to crack. Cracks in the heat exchanger may lead to the escape of toxic combustion gases that will enter the air moving into the house. Corrosion in other parts of the furnace will also affect important components, but the heat exchanger is the biggest worry. 

If you see corrosion on any part of your furnace, it’s a reason to have the heat exchanger inspected to see if it has corrosion developing and whether there are already cracks. A cracked heat exchanger must be replaced because of the danger it presents. 

Furnace Age

When rust appears on a furnace, it usually happens when the furnace has been in use for a long time, over 15 or 20 years. We strongly recommend that you replace a rusting furnace this old. Although there may be parts that can be repaired, the rust is a major caution that the furnace is far past its prime and may pose hazards in the future. You can trust our professionals to help you make the best decision for your heating and safety.

Robbins Heating & Air Conditioning serves Colorado Springs and the surrounding area. Call us when you need any help with your furnace.

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