Light rust on a furnace is common, and most of the time it is cosmetic. Rust that flakes off inside the burner compartment, or rust on the heat exchanger itself, is a different story and deserves a technician’s eyes. Here is how to tell the two apart, what causes furnace corrosion in Sacramento-area homes, and what to ask about at a fall tune-up.
Rust can appear in four places, and each means something different.
Rust needs moisture and time. In a furnace, the moisture usually arrives one of these ways:
Furnaces in closets and garages tend to rust more often than furnaces in open utility rooms. A closet traps humidity from a nearby laundry area. A garage adds a damp concrete slab, wet cars, sprinkler overspray, and a door that opens to the weather. Both are worth a closer look every fall.
Many Roseville and Sacramento houses are tract homes built from the 1970s to the 2000s with the air handler in the attic, so that is one more place worth a look.
Surface rust is usually nothing to worry about when all of these are true:
In that case, fix the moisture source, wipe the area dry, and touch up the exterior with rust-inhibiting paint if you like. Do not scrape or paint anything inside the burner compartment or on the heat exchanger.
The heat exchanger is the barrier between combustion gases and your indoor air. If rust eats through it or a crack forms, those gases, including carbon monoxide (CO), can mix into the air your blower pushes through the house. Not every rusty furnace has a failed heat exchanger, and only a technician can tell, but these signs call for a closer look:
If a CO alarm sounds, turn the furnace off, get everyone outside into fresh air, and call the fire department from outside. Working CO alarms near sleeping areas are a smart backstop in any home with gas appliances. If a technician does find a rusted-through heat exchanger, the answer is generally replacing the furnace rather than patching it. See furnace installation and replacement for what that involves; we install Amana.
Fall is the right time to catch corrosion, before the furnace runs for months. These are the places rust hides, and they are worth pointing out to the technician at a heating tune-up:
The Bronco maintenance plan is $14.49 a month per system, with a cooling tune-up in spring and a heating tune-up in fall. Learn more about AC and heating maintenance.
Call us if you see flaking rust inside the burner compartment, rust holes, soot, yellow flames, or water around the base of the furnace, or if rust comes back after you have dried and wiped it. Our furnace and heating repair team will look at it, find where the moisture is coming from and tell you what they found ($89 service call). If you are in Sacramento, see furnace repair in Sacramento.
Call Bronco at 916-675-1062, Monday to Friday, 8 to 5. Tell us what the furnace is doing.
Monday to Friday, 8am to 5pm.
Rust is something you can see, and so is a failed part. This is a Google review from a Bronco customer about a repair where the old part was handed back after the job, word for word.
“I found the technician to be highly competent, a good communicator, and on time. … The old circuit board was provided after the job and it clearly had heat/electrical damage, probably caused by the wiring.”
Yes. Light surface rust on the outside cabinet is common, especially in garages and closets, and is usually cosmetic. Look for the moisture source and mention it at your next tune-up.
It can if rust or a crack has opened the heat exchanger, but that is the exception. Rust on the cabinet does not carry the same risk. A technician can check the heat exchanger and measure CO at the vent, which is why an annual inspection beats guessing from the outside.
On the exterior cabinet, after the moisture problem is fixed and the surface is dry and clean, yes. Never paint or scrape inside the burner compartment, on the burners, or on the heat exchanger.
Once a year, in the fall, before the heating season starts. If your furnace is in a garage, closet, attic, or crawlspace, ask the technician to look at the cabinet base and flue closely.
