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Rust on Your Furnace? Here’s What it Means

Rust on Your Furnace? Here’s What it Means

Your furnace, unlike a boiler, does not need water to function, and there are no water leaks in the vicinity – so why is it rusty? While a rusting furnace may seem odd, it may indicate a more significant issue. It’s one of the things that a reputable, experienced heating repair business would check for while conducting maintenance and repairs.

What Could Rust on Your Furnace Mean?

  • Rust On The Surface: While surface rust caused by a nearby moisture source is unlikely to be a significant concern, it may signal severe interior problems. Even if you notice rust on the surface of your furnace, avoid using it until an expert HVAC technician verifies that it is safe to use.
  • The Heat Exchanger is Rusted: Rust on the heat exchanger, an internal system component, often goes unnoticed by the average homeowner. This is why preventive furnace maintenance is critical every year. When rust spots develop on the heat exchanger, it indicates that the heat exchanger may fracture. A corroded or broken heat exchanger should be replaced or repaired promptly to prevent hazardous, possibly lethal combustion gases such as carbon monoxide from entering your house.
  • Condensate Line Or Flue Clogged Or Obstructed: When exhaust and drain lines get clogged, the minute fluid produced during gas combustion is not adequately removed, increasing the risk of moisture exposure and corrosion inside the system (such as the heat mentioned above exchanger).
  • Seniority: Using the same furnace for years will result in corrosion due to prolonged exposure to combustion, making older systems more prone to exhibit rust on the heat exchanger. If your furnace is older than 15 long years, replacing it is a better investment than repairing it. These systems may only achieve 60-80% efficiency, compared to modern Energy Star systems that achieve up to 97 percent efficiency, guaranteeing a quick return on investment and a more pleasant home environment.

How Does Rust Form in The Absence Of Water?

Water vapor is present in the combustion gas collected in the heat exchanger of your furnace. Water vapor may form when these gases cool. This water vapor is condensed in a second heat exchanger in high-efficiency condensing furnaces, releasing additional heat. This is how the heat exchanger’s metal gets exposed to water, resulting in rusting. However, it would help to evacuate this moisture out via the condensate line and flue under normal operating conditions.


In general, if you detect rust on the furnace’s outside, this indicates that the device is most likely in need of replacement. Rust and corrosion pose an unacceptable danger to your furnace since they may leak gases into your house if the pollution creates a large enough leak.

In any scenario, a rusty furnace is likely several years old and in need of repair. New furnaces are much more efficient than older models, especially if you select one with a high annual fuel usage efficiency (AFUE), and your new installation may have unmatched power and safety features.

Is your furnace rusty? Arrange for emergency service and repair immediately. Ameritech Air Conditioning and Heating provide complimentary 24/7 servicing, ensuring the safe functioning of your furnace. To schedule repair and maintenance, contact by dialing (407) 743-7106 or visiting their official website. You can also search for the best furnace repair Orlando or heating service Orlando fl on your internet.