Rust is fairly common on old furnaces, and it could be a sign that you'll have to replace your furnace in the near future. However, many things cause rust, and rust isn't always a serious sign. Since rust could indicate a problem with your furnace, you should call a furnace repair company when you see rust, especially if it's inside the furnace. Here are three causes of furnace rust and the repairs that might be needed.

1. Rust From A Clogged Condensation Drain

If you have a central air conditioner, it probably shares the air handler with your furnace. An AC makes condensation, and when water and metal mix, rust can potentially form. A high-efficiency furnace can make condensation too, and it normally drains from the air handler so rust doesn't form. The condensation in the air handler usually drains out of the house or down a drain and doesn't pose a problem. If the drain gets clogged, water can spill on the floor or back up in the air handler and lead to rust.

If rust developed due to a clogged condensation drain, the furnace repair person can unclog the drain and make sure the drain and pan are functional. They might even suggest installing a float switch that shuts down the HVAC if the drain pain gets too full and on the verge of overflowing.

2. Rust From Combustion Gases

Rust from combustion gases could be more serious. Combustion gases cause rust to develop on the inside of your furnace. The combustion area and burners might get coated with rust. A furnace repair technician might be able to clean these parts off to get rid of the rust, but if not, the parts can be replaced.

Rust can even go deeper into your furnace and affect the heat exchanger. A rusted heat exchanger is a serious furnace problem. This condition is more likely to happen when your furnace is old, so the repair technician might recommend you get a new furnace rather than sink a lot of money into replacing the heat exchanger.

3. Rust From A Leaking Humidifier

If you have a humidifier on your furnace, it's a source of potential leaking. The humidifier always contains water, so if there's a leak, water will contact the metal of your furnace and rust may develop. The repair technician can repair the humidifier and stop the leak, and they might be able to remove the rust to keep it from spreading.

Rust can become a big problem for your furnace because it spreads. It's important to stop the source of moisture and remove the rust when possible so you can extend the life of your furnace.

Contact a local HVAC technician to learn more about furnace repair.