Measuring and Installing a Chimney Chase Cover

What the Fireplace Maker Says About the Chase Top

A chase cover on a factory-built fireplace is not just sheet metal; it is part of how the chimney ends. Section R1005.1 of the 2023 Florida Building Code, Residential, says factory-built chimneys are installed and terminated in accordance with the manufacturer's instructions, so those instructions come first.

The Superior WRT wood fireplace instructions show what they can contain. For one chase-top termination, the chase's shortest side must be at least 30 inches high with an inside dimension of at least 19 inches, and the last pipe section ends no more than 6 inches below the chase top. For a round-top termination, the pipe ends at least 6 inches above it. The flashing is cut with a 16-1/2 inch hole and a 2 inch collar, and the note on the drawing is plain: do not seal ventilation openings. Your fireplace's manual may give other numbers.

Measurements for the Fabricator

A replacement cover is made to the chase you have, so the numbers have to be taken on the roof, outside the trim, to the nearest eighth of an inch. Write each one on a sketch of the chase top seen from above, with the downhill side marked.

Two people make this safer and more accurate: one on the roof with the tape, one on the ground writing it down and keeping an eye on the ladder.

• Length and width across the outside of the chase, siding and trim included.
• Skirt depth: how far down the sides the new cover should hang.
• Pipe position: from the center of the pipe to two adjacent outside edges.
• Pipe size: the outside diameter where it passes through the cover.
• Collar height: from the cover surface to where the storm collar sits.
• A second pipe or vent, if any, with its own position and size.
• The chase's squareness: measure both diagonals; if they differ, note by how much.

Shape Choices to Make Before Ordering

The fabricator will ask about the top and the metal. A flat top is the most likely to hold water; a cross break or a sloped top sheds it. A drip edge at the bottom of the skirt throws water clear of the siding. Our page on chase cover metals covers galvanized, stainless, aluminum and copper, and how long a cover lasts explains why the shape matters as much as the metal.

Two Flues in One Chase

Some chases hold two chimneys. The Superior Pro Series instructions suggest separating terminations by at least 24 inches center to center and staggering their heights by 18 inches, so smoke from one does not spill into the other. A cover for that chase needs both holes in exactly the right places, and its maker should know which termination sits in each.

If the old cover had one hole for two pipes, or a pipe that sat off-center in its collar, note that too; it often explains where the water came in.

Installing It

The steps below follow the Superior WRT chase-top sequence, with the sealing step from the Majestic MPL11 manual. They assume the old cover is off, the framing under it is sound and dry, and the termination is the fireplace maker's listed part.

• Set noncombustible spacers at the corners of the chase top, as the instructions call for.
• Lower the cover over the pipe so the collar centers on it, skirt down the sides.
• Fasten through the side skirt into the framing, never through the flat top.
• Fit the termination or sleeve over the opening and secure it as its instructions say.
• Place the storm collar around the pipe and seal its joint with the pipe; Majestic presses mastic into that gap, Superior caulks it.
• Leave the maker's ventilation openings open.

Doing It Yourself, Honestly

Measuring a chase is not hard; getting to it is. The work is done at the top of a box on a pitched roof, sometimes two stories up, with sharp sheet metal and no railing. The Majestic manual tells installers to wear gloves around the storm collar's edge and to watch for electrical wires near the metal chimney. A slip there is a fall, and a cover set wrong can leak, as that manual warns, rain water into the home.

If you are not equipped for roof work with fall protection, measure nothing yourself: a wrong number makes a cover that does not fit, and the whole order starts again. If you are, follow your fireplace's instructions, not this page's examples.

Having Us Measure and Fit It

Our chimney chase cover crew measures on the roof, checks the framing under the old pan, has the cover made to the chase and fits and seals it, then cleans up and hauls the old metal away. A free inspection comes first, and the written estimate follows before anything is ordered.

We run a local, family-owned chimney business, the measuring is done by experienced people who fit chase covers themselves, and we are Proudly American. Spring Hill homeowners get the same Proudly American family crew on the roof that they meet at the door.