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What Causes Your Furnace To Rust?

Furnace rust new york

A furnace is an investment that should last more than a decade if it is properly maintained by a professional heating contractor. But nothing lasts forever, and eventually you’re going to see telltale signs of age on your heating system.

One of those signs is rust, which can be a serious problem in a furnace – especially if the rust occurs in the ventilation or heat exchanger areas. Corrosion in these places could eventually lead to a release of dangerous combustion gases (carbon monoxide, sulfur dioxide, and nitrous dioxide) into your living area – something you definitely want to avoid.

With that in mind, the obvious questions become what causes rust on a furnace, and how do you prevent it? Let’s take a look.

Three common causes of furnace rust

Here are three common reasons for rust formation on your furnace, and what you can do to prevent each.

1. Leaks or high humidity – Water from nearby pipe or rainwater leaks can cause moisture buildup near your furnace, and an over-humid home can force moisture to accumulate in the return ducts of your heating system.


  • Invest in waterproofing measures such as better drains, downspouts, caulking and weather stripping.
  • Address any plumbing issues promptly (call a professional plumber; don’t do it yourself!).
  • Consider managing humidity with a whole-house humidifier/dehumidifier.

2. Air conditioner leaks – In many HVAC systems, your furnace and air conditioning units are installed very close to one another – in some cases, one is directly on top of the other. If your AC leaks, that moisture can get in the furnace. A cracked drain pan or clogged condensate line can also leak into your furnace, eventually causing rust.


3. Exhaust problems – As hot gases and vapors move away from the heat of the burner and toward the flue through the heat exchanger, they may cool and form water vapor, which can pool and corrode the heat exchanger and flue.


If your furnace is more than 15 years old and you notice signs of corrosion, it’s time to think about a furnace upgrade – Contact Black Bear today to get a FREE, no-obligation estimate on a new, high-efficiency furnace for your Sullivan County home!