By Daniel Watkins, Noble Chimney Sweepers.
If you have noticed orange-brown streaks running down the siding beneath your chimney, the culprit is almost always a rusting chase cover. It is one of the most common chimney problems we find on factory-built fireplaces in Frankfort and the surrounding Will County subdivisions, and it is also one of the most ignored, because homeowners assume the stain is a paint problem rather than a water problem.
What is a chase cover, and why does it rust?
A chase cover is the metal lid that seals the top of a chimney chase, which is the boxed-in wood-framed structure that surrounds a factory-built (prefabricated) fireplace. Unlike a masonry chimney topped with a poured concrete crown, a prefab chase is capped with sheet metal. Many builders in the 1980s through the early 2000s used galvanized steel, which is inexpensive but corrodes once its coating wears through. Add twenty-plus Illinois winters of snowmelt, freeze-thaw cycling, and standing water on a cover that was cut flat instead of sloped, and rust is not a possibility, it is a schedule.
Those orange streaks are a warning, not a cosmetic issue
The stain itself is harmless. What it tells you is not. Rust streaking means water is sitting on the cover long enough to corrode it, and a corroded cover eventually perforates. Once water gets past that lid it enters a chase built from wood framing and plywood sheathing, where it soaks insulation, rots the framing, and reaches the firebox and flue components from the outside. By the time a homeowner smells must or sees a ceiling stain near the fireplace, the repair is no longer a piece of sheet metal, it is carpentry.
How to check yours from the ground
You do not need to get on the roof. Stand back far enough to see the top of the chase and look for three things: rust bleeding at the corners or seams, a cover that appears flat or dished rather than sloped, and any visible sagging in the middle where water can pool. Then walk the siding directly below and check for streaking, soft spots, or blistered paint. Our DIY chimney maintenance guide walks through the rest of the ground-level checks a homeowner can safely do without ladders.
A chase cover is not a chimney crown
These two get confused constantly, and the difference matters when you are calling for service. A crown is the sloped masonry slab on top of a brick chimney; a chase cover is stainless or galvanized metal on top of a framed chase. They fail differently and they are repaired differently. If you are unsure which one you have, our page on chimney caps and crowns explains both, and any of our technicians can identify yours in a few minutes on site.
What replacement actually involves
A proper replacement is custom fabricated to your chase dimensions, not pulled off a shelf. We measure the chase, build the cover with a cross-break or slope so water sheds instead of ponding, add a drip edge that carries runoff clear of the siding, and cut collars sized to your existing flue. Stainless steel is the material worth paying for here, because it is the difference between doing this once and doing it again in fifteen years. We give you the price up front before any work starts, and our pricing page is the only place our numbers live, so you are never guessing.
Late summer is the window
Fixing a chase cover in August means working on a dry roof in reasonable weather. Waiting until you smell smoke backing up in November means competing with everyone else who waited, in worse conditions. If your chimney has not had a look in the past year, a chimney inspection covers the cover, the flue, the firebox, and the clearances in a single visit.
Noble Chimney Sweepers is certified, bonded and insured, and owner-operated. I have spent 14 years on chimneys in this part of the Chicago area, and I still find rusted-through chase covers on homes whose owners had no idea anything was wrong. If you are in Frankfort and you see streaking, call (708) 432-5747. We answer 7 days a week, 7 AM to 7 PM.
Frequently asked questions
Can I just paint over the rust streaks on my siding?
You can clean the siding, but painting does nothing to the source. The streaks will return within a season because the cover above is still corroding and still shedding rust every time it rains.
How long does a galvanized chase cover usually last?
In this climate, galvanized covers commonly begin showing rust within 10 to 20 years, and the ones that pond water fail sooner. Stainless steel covers last substantially longer, which is why we install them.
Is a rusted chase cover a fire hazard or a water hazard?
Primarily a water hazard. The danger is rot and hidden structural damage inside the chase. It becomes a safety concern indirectly, when water corrodes the flue components or degrades the clearances around the firebox.
Can a chase cover be repaired instead of replaced?
Occasionally a small isolated pinhole can be sealed as a short-term measure, but once rust is widespread or the metal has thinned across the panel, patching buys months, not years. Replacement is the honest answer in most cases.
Do I need a chimney cap too, or is the chase cover enough?
They do different jobs. The chase cover seals the top of the chase; the cap sits over the flue opening and keeps rain, birds, and debris out of the flue itself. Most prefab chimneys need both working correctly.
How do I know if I have a prefab fireplace or a masonry one?
Look inside the firebox. Factory-built units typically have metal panels, refractory panels with visible seams, and a metal manufacturer’s plate. Masonry fireplaces are laid brick or firebrick all the way through.
Will insurance cover chase cover damage?
Gradual rust and wear are normally treated as maintenance rather than a covered loss, though sudden storm damage can be a different conversation. Your carrier is the only one who can answer this for your policy.
How long does a chase cover replacement take?
Once the custom cover is fabricated to your measurements, installation is usually a single visit. The measuring appointment and the install are separate steps because the cover is built to your chase, not stocked.
Published August 16, 2026