The construction of a DIY outside metal chimney, or prefabricated metal chimney, follows the same basic procedures as for an interior installation, except most of the installation is routed along an exterior wall. A metal chimney serves the same purpose as a masonry chimney: create a draft to draw the oxygen required for the appliance combustion process and exhaust smoke, fumes, embers and gases through the chimney.
Like all chimneys, an outside metal chimney must be well-constructed. It must be assembled in a manner that meets the specifications of the appliance and the local building codes. Plan the layout of the chimney as close to the appliance as possible. Usually, this is an adjacent wall.
The materials used for the construction of interior chimneys are the same as used for DIY outside metal chimney projects. Use double-wall (insulated) or triple-wall pipe. The formal Underwriters Laboratories (UL) label is UL-approved Stainless Steel Class A Insulated Chimney. The insulated chimney pipe is used the most. Insulated pipe is constructed of two layers of pipe, with 1 or more inches of a heat-resistant insulation sandwiched in between the stainless steel pipes.
Triple-wall chimney pipe consists of three pipes. It is constructed in a manner that allows air to circulate between the pipes, which gets rid of surplus heat. It doesn’t matter which pipe you select for your DIY outside metal chimney as long as the pipe is listed by Underwriters Laboratories.
Read the product owner manual and follow the local building codes for constructing the metal chimney. Chimney pipes come in a variety of diameters. The size of the chimney pipe you should use is usually based on the port size. The port is located on the appliance. Increasing or decreasing the pipe size recommended by the manufacturer can harm the appliance’s performance. It can also void the product’s warranty.
Generally, the DIY outside metal chimney exits through a wall adjacent to the appliance. Install a chimney pipe wall thimble in an opening between two studs. The wall thimble allows you to pass chimney piping through the combustible wall framing. The stainless-steel insulated pipe must be stacked vertically, and to a minimum height as specified in the manual and per building codes.
Most chimneys have the same height requirements: the chimney must extend a minimum of 3 feet above the chimney line and 2 feet higher than any object within a 10-foot radius. Attach a roof vent cap to keep birds and debris out of the system.
Although it may not be required in all locations, you may want to construct a chase to round off your DIY outside metal chimney. A chase is a wooden frame construction that encases the chimney. The enclosure can be finished with material to match the existing building finish.
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