Rusty Chase Covers and Caps

Not Every Chimney Is Brick

Drive through many Thousand Oaks neighborhoods and you will see chimneys clad in stucco or siding rather than brick. Most of those are not masonry chimneys at all. They are wood-framed boxes, called chases, built around a factory-built fireplace and its metal chimney pipe. Factory-built fireplaces were installed widely from the 1970s onward, and they make up a large share of the fireplaces we see in the Conejo Valley.

These systems leak too, and they leak in their own ways. The most common one is a part most homeowners have never heard of: the chase cover.

What a Chase Cover Does

At the top of the chase sits a metal pan that covers the open top of the wooden box. The metal chimney pipe passes up through a hole in the middle of it, and a termination cap sits on top of the pipe. The chase cover is the roof of the chase. Its job is to shed rain off the top and keep it out of the framing below.

Many original chase covers were made from thin galvanized steel and formed as a flat pan. That combination is the problem. A flat pan does not shed water well. Rain pools in the middle, often around the pipe collar, and sits there. Galvanized coating wears off, the steel rusts, and eventually small holes open up. Water that gets through runs straight down inside the chase, along the chimney pipe and the framing, and into the house.

Signs of a Failing Chase Cover

You can often spot the problem from the ground or a ladder.

• - Rust streaks down the side of the chase. Orange or brown stains running down the stucco or siding from the top are a clear sign the cover is rusting.
• A sagging or dished top. A cover that dips in the middle holds water.
• Water in the firebox or on the hearth. Water running down inside the chase can reach the firebox and leave rust on the steel floor or the grate.
• Stains on the ceiling or wall near the fireplace. The chase is often built against an exterior wall, and water inside it can show up anywhere along that wall.
• Rotted siding or soft wood at the top of the chase. In bad cases the framing itself is damaged.

Inside the firebox, rust on the steel floor and cracked or crumbling refractory panels can be late signs of the same leak.

Why It Matters More Than It Looks

Water inside a chase does more than stain a ceiling. It soaks the wood framing, which can rot over years. It rusts the chimney pipe sections, and since those pipes carry hot exhaust, rusted or separated joints are a safety concern. It reaches the firebox, where rust weakens the steel and moisture breaks down the refractory panels. By the time a leak shows inside the house, the cover may have been failing for several winters.

Replacing a Chase Cover

The fix is usually a new chase cover, and the details are what make it last.

• - Material. Stainless steel holds up far longer than galvanized and does not rust through in a few years. Copper is another long-lasting option.
• Shape. A good cover is not flat. It has a raised center or crossed breaks that slope it toward the edges, so water runs off instead of pooling.
• Drip edge. The edges should turn down over the sides of the chase and project slightly, so water drips clear rather than running back under onto the siding.
• Fit. We measure the top of the chase exactly. Covers are made to size, and one that is too small or too large will leak at the edges.
• Collar and cap. The collar where the chimney pipe passes through needs a storm collar to shed water away from the hole, and the termination cap on top should be the one listed for that chimney pipe, because factory-built chimneys are tested and listed as complete systems.

If the framing at the top of the chase has rotted, that is repaired before the new cover goes on. Chase cover replacement is quoted in writing after we have measured and looked at the condition of the chase.

The Termination Cap

The cap on top of the chimney pipe is a separate part with its own job: keeping rain out of the flue and catching embers. On factory-built systems it must be the cap designed for that brand and size of pipe. Generic caps can disturb the draft or the airflow the system was tested with. Damaged or rusted caps are replaced with listed parts. Our chimney cap installation page covers caps in more detail, with installed prices from $155 to $635.

What Happens to the Fireplace

If a leak is caught early, replacing the cover and cap is usually the whole job. If water has been getting in for many years, the firebox may have rusted or the refractory panels may be cracked. Panels can usually be replaced with parts made for that model. A firebox with a rusted-through floor, or a unit whose parts are no longer made, may be better replaced than repaired. We will show you photos and explain both choices. If you are thinking of a change, a gas insert or a new direct-vent unit may suit, and our fireplace inserts page explains what that involves.

Keep an Eye on the Top

Chase covers are out of sight, so they get forgotten. A look from a ladder or a pair of binoculars once a year, ideally before the rainy months, is enough to catch rust streaks and sagging early. If you see them, or find rust in the firebox, book an inspection through our contact page. A Level 1 inspection with us is $52.