Introduction: How to Install a Metal Chimney Kit

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Adding a heating appliance to your home can often cost more than the price of the appliance and its installation. Unless you’re talking about electrical- resistance baseboard units, your new heater will create warmth through combustion, and, in the process, waste gases that must be expelled from the living area. So, in addition to the fireplace, furnace or heater, you’ll need a chimney—and here’s where things can get difficult. Masonry chimneys are big undertakings.

Not only is the cost of materials—brick or block, mortar and liner—a consideration, but the labor involved in laying the chimney is more than what most homeowners have in mind for a weekend project. Masonry chimneys require a foundation and may involve significant alterations to the house—especially if the chimney is inside. Thankfully, there’s an alternative.

Specially designed metal chimneys are available to handle a wide range of heating appliances—from wood-burning stoves to conventional furnaces. Faced with the need for a chimney in a garage/workshop conversion, we opted for a Metalbestos insulated stainless steel chimney manufactured by Selkirk Inc., 14801 Quorum Dr., Dallas, TX 75240; The Metalbestos system we used, the Model SSII Type HT, features double-wall, insulated stainless steel pipe that’s available with inside diameters of 6, 7 and 8 in. The lengths simply thread together for fast assembly.

In addition to the pipe, you’ll need various components to support and finish your chimney. These are available in kits tailored to the specific types of installation. We used a flat ceiling kit with which the chimney is supported on the ceiling joists. Other kits include a pitched ceiling kit that handles cathedral ceilings and a kit for running the chimney through an exterior wall and up the side of a structure.

The big advantage of a metal chimney is ease of installation with minimal site modification. However, this convenience carries a price. A 36-in. length of the 6-in. pipe we used retails for about $118—that’s a little over $3 per inch. And, there’s the cost of the roof and support accessories. Metalbestos SSII chimney systems carry a 10-year limited warranty.

This project was originally published in the December 2000 issue of Popular Mechanics.  You can find more great projects at Popular Mechanics DIY Central.

Step 1: Ceiling Work

If possible, plan your flue location to fall between the building’s ceiling joists and the rafters. The 6-in-dia. pipe requires a 121⁄4-in. square frame to hold the chimney support bucket—the ceiling fixture that carries the inside end of the chimney. After removing any insulation over the area, lay out a 121⁄4-in. square on the ceiling and cut the hole with a sabre saw or drywall saw (Fig. 1).

Measure the space between the ceiling joists and cut framing members to fit around the perimeter of the opening. In the attic space, nail the crossmembers between the joists on the sides of the ceiling cutout. Then, finish the framing (Fig. 2), and move back downstairs to secure the ceiling around the opening with drywall screws.

Step 2: Support and Flashing

Prepare to install the chimney support bucket by temporarily screwing two wooden strips along opposite sides of the opening. Place these strips just inside the cutout edges (Fig. 3). Then, from above, lower the bucket in place and let it rest on the strips. Start a few 8d nails through the holes in the side of the bucket, check that the piece is level and finish driving the nails.

Drive 8d nails through the remaining bucket nail holes (Fig. 4). With the support bucket in place, remove the strips and install the square ceiling-trim plate by driving screws up into the framing (Fig. 5). Inside the attic space use a plumb bob or level to transfer the center of the support bucket opening to the underside of the roof deck. Then, bore a hole through the roof at the chimney center so that it will be visible outside. Move to the roof and locate the center hole.

Align the chimney flashing over the hole so that it’s centered and check with a level. Then, reach into the flashing and use a utility knife to scribe the shape and location of the chimney hole. Remove the flashing and cut away the shingles (Fig. 6). Use a reciprocating saw or sabre saw to cut through the roof decking (Fig. 7). To install the flashing, first carefully pry up the shingles around the outer edges of the upper half of the hole. Use a flat pry bar for the job and remove any roofing nails that are in the way.

Then, slide the flashing under the lifted shingles (Fig. 8) and double-check that the flashing is centered properly and that the roof hole will provide at least 2 in. of clearance around the pipe. Relift the shingles and the edges of the flashing and apply roofing caulk. Then, nail along the top and sides (Fig. 9) and add a dab of caulk over the exposed nailheads.

Step 3: Pipe Installation

Back inside, thread the smokepipe adapter to the first length of insulated pipe (Fig. 10). The adapter is single-wall pipe that mates with the flue pipe from your heating unit. From the attic, slide the assembly into the support bucket (Fig. 11). Move back downstairs and use a nutdriver to secure the pipe adapter to the bucket with sheetmetal screws (Photo 12).

Thread together enough pipe to reach from the installed length through the flashing (Fig. 13) and slide the pipe up through the flashing. Install the supplied ring clamps to secure the joints between each pair of pipes. On the roof, install the storm collar by sliding the tabs of one end into the slots on the other (Fig. 14). Bend the tabs over and slide the collar down to the flashing. Apply a bead of silicone caulk to seal the joint between the storm collar and the chimney (Fig. 15).

To keep attic insulation away from the chimney, install the two-piece metal insulation shield. Simply join the halves around the chimney (Fig. 16) and nail the shield to the framing (Fig. 17). Then, place the collar over the shield (Fig. 18). Add the required lengths of chimney to bring the height to the appropriate distance above the roof, secure joints with ring clamps and attach the weather cap. Note that chimneys extending more than 4 ft. above the roof will require bracing.