Chase Covers: The Part of a Factory-Built Chimney Nobody in Joliet Checks
By Dan Joel, Elite Sweepers Inc.
Plenty of homes here do not have a masonry chimney at all. What they have is a factory-built fireplace venting through a metal flue, with a framed wooden chase built around it and finished in siding to look like a chimney from the street. It works well. It also has a specific failure point that masonry chimneys do not, and it is at the top where nobody looks.
What a chase cover is
The short answer: the metal lid closing the top of the framed chase, with the flue passing through it.
On a masonry chimney, the top is a concrete crown. On a framed chase, it is a sheet metal cover, sloped to shed water, with an opening the flue pipe passes through and a collar sealing around it. That cover is the only thing standing between weather and a wooden box built into your house. Everything below it, the framing, the sheathing, the insulation, is combustible material that must stay dry.
Why so many of them fail
The short answer: they were commonly made from galvanized steel, which rusts.
A great many chase covers were installed in galvanized steel because it is inexpensive. Galvanized rusts, and a chase cover is a horizontal surface holding water in the middle of a roof. The failure sequence is predictable: the surface rusts, water pools in the low spots, the rust becomes a pinhole, and the pinhole becomes a hole. Some covers were also built flat rather than sloped, which guarantees standing water and accelerates all of it.
Stainless steel and copper do not have this problem, which is why they are what a replacement should be made from.
How to tell yours has gone
The short answer: rust streaks down the siding, water inside the firebox, and staining on the ceiling near the chase.
- Rust streaking on the exterior. Orange-brown runs down the siding below the top of the chase are the clearest visible sign from the ground.
- Water in the firebox. Drips or standing water after rain mean it is coming in from above.
- Ceiling or wall staining next to the chase. Water getting into the framing rather than down the flue.
- Rust on the firebox or damper components. Metal parts corroding where they should stay dry.
- A musty smell around the fireplace. Damp framing inside an enclosed chase.
Why this one gets expensive when it is left
The short answer: the damage is to wood framing you cannot see.
A masonry chimney taking on water deteriorates slowly and visibly. A chase is a wooden structure, and water entering through a failed cover soaks framing and sheathing inside an enclosed cavity with poor drying. By the time it produces a visible stain indoors, the material inside has usually been wet through repeated cycles. Replacing a chase cover is a modest job. Repairing rotted chase framing is not, and the difference between the two is how early it was caught.
What replacement involves
The short answer: a properly sized stainless cover with a cross-break for slope and a correctly sealed collar.
The cover should be fabricated to the actual dimensions of the chase, formed with a cross-break or slope so water runs off rather than pooling, and sealed properly where the flue passes through. A cap over the flue itself is a separate component and needs to be sound too, which our chimney caps and crowns page covers.
Getting it assessed
The chase cover and the flue termination are examined during a chimney inspection, and related work is covered on our chimney repair page. For local scheduling, see our chimney service in Joliet, with costs on our pricing page.
Elite Sweepers Inc is insured and bonded, works seven days a week from 7 AM to 7 PM, and gives you the price up front. Call (708) 432-3977.
Chase Cover and Prefab Chimney Questions
What is a chimney chase cover?
It is the metal lid closing the top of a framed chimney chase on a factory-built fireplace system, with the flue passing through it. It does the job a concrete crown does on a masonry chimney, keeping water out of the structure below.
How do I know if I have a chase instead of a masonry chimney?
Look at the exterior. A chase is framed and finished in siding rather than built of brick or stone, and it is topped with a metal cover rather than a concrete crown. Factory-built fireplaces almost always vent through one.
Why does my chase cover rust?
Most commonly because it was made from galvanized steel, which corrodes on a horizontal surface that holds water. Covers built flat rather than sloped make it worse, because water pools instead of running off.
What should a replacement chase cover be made of?
Stainless steel or copper, formed with a cross-break or slope so water sheds rather than pooling, and fabricated to the actual dimensions of the chase with a properly sealed collar where the flue passes through.
What happens if a failed chase cover is left?
Water enters an enclosed cavity containing wood framing and sheathing that dries poorly. Replacing the cover is a modest job, while repairing rotted framing is a much larger one, so catching it early matters considerably.
Are rust streaks on my siding a problem?
They are usually the earliest visible sign from the ground that the chase cover is corroding. The rust is being carried down the siding by rainwater running off a cover that is deteriorating.
Do factory-built fireplaces need annual sweeping?
Yes. They produce creosote like any wood-burning appliance, and the flue, the cover, the cap and the unit itself all need annual attention. Manufacturer specifications also matter more with these systems than with masonry.
Is the chase cover the same as the chimney cap?
No. The chase cover closes the top of the framed chase, while the cap sits above the flue opening itself to keep rain, animals and debris out of the flue. A chase needs both, and either can fail independently.
Published September 26, 2026