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Is your furnace showing signs of rust? This can be a perplexing issue for many homeowners because, unlike an air conditioner or water heater, heating systems don’t contain water. Despite being less common, furnace rust is still a very real problem and can indicate a number of underlying issues. The best way to diagnose why your furnace is rusting is to have the unit inspected by a licensed HVAC technician. At Reliable Ducts Heating & Cooling, our technicians have many years of experience repairing and replacing rusty furnaces in Jacksonville and the surrounding areas. We’ll send out a specialist right away to inspect your system and determine the cause of the rust.

In the meantime, this article will give you some insight into the most common causes of furnace rust and how to avoid a rusty furnace.

How Common Is Furnace Rust?

A rusty furnace is not as common as a rusty air conditioner, but that doesn’t mean your furnace is safe from rust. A number of factors, from infrequent maintenance to old age, will cause your furnace to rust. Furnace rust is most common on the exterior of the furnace and along the heat exchanger. The danger of rust is that it weakens the underlying metal, which can eventually lead to broken furnace components. While most types of furnace damage only lead to an unpleasantly cold house, some damage can increase the risk of house fires and carbon monoxide leaks.

Furnaces most commonly develop rust when metal components are repeatedly exposed to combustion gases. As the furnace goes through a heating cycle, gas inside of it is heated up before being allowed to cool down. It’s the cool-down stage of this process that generates water vapor. If the vapor isn’t properly vented from the furnace, it will corrode the interior of the furnace, leading to mechanical problems in the future.

Why Do Furnaces Rust?

Excessive humidity: Whenever metal meets humidity, there’s sure to be rust. Atmospheric moisture can weasel its way into your heating system through air ducts. This is especially common after a rainstorm or during humid weather. Once even a small amount of moisture enters the system, it can trigger a chemical reaction with metal that creates rust. If your ducts have breaks or separations in them, they’ll draw in additional moisture, which can do a lot of damage to your furnace.

Combustion vapor: In a gas-powered furnace, the heat exchanger houses combustion gas which cools down into a liquid vapor. Normally, this vapor is vented out of the furnace via an exhaust pipe. But if the pipe is clogged or blocked, the vapor will instead be trapped inside the furnace, causing the metal surface to rust.

Leaky air conditioner: The most common residential HVAC set-up is an air conditioner installed directly above the furnace. This allows both units to share the same blower. Air conditioners generate a lot of moisture during operation, and if the system is properly maintained, that moisture will be safely drained via a drain pan. However, if the drain is clogged or obstructed, the pan will overflow and leak down onto the heater. This issue is especially costly because it requires both the AC and furnace to be repaired.

Different Types of Furnace Rust

Your furnace can develop rust on a range of different surfaces and components. The location of the rust can indicate what’s causing it and how serious of a problem it is. These are the most common types of furnace rust we see:

Surface rust: The exterior shell of the furnace will begin to rust if it’s exposed to a nearby source of moisture. While this isn’t necessarily a major issue, you should confirm that the rust hasn’t spread to the inside of the unit. A certified HVAC technician will do a careful examination of the unit’s interior to look for signs of corrosion and moisture damage.

Heat exchanger: Your furnace’s heat exchanger is an internal component responsible for transferring thermal energy. Even small spots of rust can weaken the metal to the extent that cracks can form. When heat exchangers crack, they can release toxic fumes into the home, including exhaust and carbon monoxide. Since the heat exchanger is hidden inside the furnace, many homeowners don’t realize the component is rusty until it breaks. Luckily, this is exactly the type of damage we look out for during an annual furnace tune-up.

Blocked Flue or Condensate Line: Your furnace contains a flue and drain lines that are used to transport combustion byproducts out of the heating system, including a small amount of moisture. If these components get blocked, the fluid is trapped in the furnace and will begin to corrode nearby components.

Old age: Older furnaces are more likely to have rust than newer units because they’ve been extensively exposed to combustion. If your furnace is more than 15 years old, it’s time to consider a replacement. A new unit will be rust-free and feature greater energy efficiency, which will save you money in the long run. You also don’t have to worry about the many maintenance issues related to furnace rust, including cracked heat exchangers, fires, and carbon monoxide leaks.

Furnaces Are Waterless, So Why Do They Rust?

Furnaces are unique among home appliances in that they use very little water. But that leads us to the question, “why do furnaces rust?” You may be surprised to learn that furnaces do produce a small amount of water vapor. As combustion gas is drawn into the unit’s heat exchanger, the gas cools down and generates vapor. High-efficiency furnaces also contain a second heat exchanger that condenses the vapor to create additional heat.

In well-maintained furnaces, moisture is safely released to avoid becoming trapped. However, if the furnace is clogged, damaged, or poorly maintained, that moisture can get stuck in the system and lead to corrosion. For this reason, it’s important to have an annual furnace tune-up. During a maintenance appointment, a technician will inspect the heat exchanger and ensure the exhaust flue and condensate lines are not clogged.

Furnace Repair or Replacement?

Rust doesn’t go away on its own; the only solutions are to have your furnace repaired or replaced. The best service option depends on the extent of the rust and what components are affected. If your furnace is still relatively young and well-maintained, we’ll probably be able to replace the rusted component. However, if your furnace is older, extensively rusted, or core components are rusted, then replacement is probably the best option.

Your Furnace Service Team in Jacksonville

When your furnace is rusty and in disrepair, you can count on Reliable Ducts Heating & Cooling to restore it to working condition. We pride ourselves on being customer-focused and offering a 100% satisfaction guarantee. As a family-owned and -operated company, you can expect that we’ll treat your home with the same level of care and respect as we do our own. We also offer 24/7 emergency service, so you can count on us to be there when you need us most. Whether you need reliable furnace repairs or a dependable furnace replacement, Reliable Ducts Heating & Cooling is the right team for the job.

Call Reliable Ducts Heating & Cooling today to schedule furnace service! We offer comprehensive cooling and heating services.

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