By Johnathan Mason, Ace Chimney Service.
Plenty of homes have what looks like a brick chimney and is nothing of the kind. Behind the siding or the brick veneer is a wood-framed box called a chase, and inside it a metal flue running up from a factory-built firebox. These systems are common in Cary and they fail in ways a masonry chimney never does. If your fireplace has a metal firebox with visible seams and a refractory panel lining, this article is about your chimney.
Masonry or factory-built — how to tell
Look inside the firebox. Masonry means firebrick laid in mortar with visible joints. Factory-built, sometimes called prefabricated or a zero-clearance unit, means a metal shell with lightweight refractory panels, usually a metal label riveted somewhere inside the opening listing the manufacturer and model. That label matters: a factory-built system is only rated as the assembly it was tested as, and parts are not interchangeable between brands.
The chase cover is the part that fails
At the top of the chase sits a metal lid the flue passes through, called the chase cover. It is the roof of the whole assembly. Many were built from galvanized steel, and galvanized steel in a climate with our freeze and thaw cycles rusts through from standing water. What we look for:
- Rust streaks running down the siding below the chimney top — visible from the ground, and the earliest warning you get.
- A cover that is flat rather than sloped, so water pools instead of running off.
- Failed sealant where the flue penetrates the cover.
- Any pinhole. Water entering there runs down inside a wood-framed chase where nobody sees it.
Why a leaking chase is worse than a leaking masonry chimney
Masonry tolerates water badly but slowly. A chase is framed lumber with sheathing and insulation, and water in it goes straight to rot and hidden mold while the fireplace still works normally. By the time a stain appears on a ceiling, the leak has usually been running for seasons. That is the honest case for replacing a rusting chase cover early rather than watching it.
Replacement, not patching
A rusted cover gets replaced, not sealed. We fabricate to the measured dimensions of the chase with a cross break so water sheds, a proper drip edge so runoff leaves the siding alone, and stainless steel rather than galvanized so the same failure does not repeat in ten years. The flue collar and storm collar are refitted at the same time, since a new cover around old sealant simply relocates the leak. Sizing, materials, and price are agreed before we start.
The rest of the system still needs service
Factory-built fireplaces need annual attention just as masonry ones do. Cracked refractory panels have to be replaced with the manufacturer’s parts. Metal flue sections can separate or corrode. Creosote builds in a metal flue exactly as it does in a clay one, so chimney sweeping and a chimney inspection apply the same. Related work is listed on the chimney caps and crowns page and across the chimney services hub, with rates on the pricing page.
Booking in Cary
Ace Chimney Service has served Cary and McHenry County for 29 years. Insured and bonded, price up front, seven days a week from 7 AM to 7 PM. Call (815) 320-0883 or use our book online page.
Frequently asked questions
What is a chase cover?
The metal lid closing the top of a framed chimney chase, with an opening for the flue. It keeps water out of the wood structure below.
How is it different from a chimney crown?
A crown is the mortar or concrete slab on top of a masonry chimney. A chase cover is sheet metal on a wood-framed chase. Different materials, different failure modes.
How do I know mine is rusting?
Look for orange-brown streaks on the siding or brick directly below the chimney top. That runoff is rust carried down by rain.
Can a rusted chase cover be sealed rather than replaced?
Sealant on rusted steel buys a short reprieve at best. Once the metal has perforated, replacement is the repair.
What material should a replacement be?
Stainless steel, sloped or cross-broken so water runs off, with a drip edge. Galvanized is what typically failed in the first place.
Do factory-built fireplaces need annual sweeping?
Yes. Creosote accumulates in a metal flue the same as in a clay-lined one, and the assembly needs checking for separated sections and cracked panels.
Can I install a masonry-style cap on a prefab chimney?
No. Factory-built systems are listed as complete assemblies and require the components specified for that model.
How long does a factory-built fireplace last?
It depends on use and water exposure. Kept dry and serviced annually they run many years; left under a leaking chase cover they deteriorate quickly.
Published August 25, 2026