- 1). Load a caulking gun with high-temperature resistant caulk and run a bead of caulk into gaps around the exterior chimney where the chimney meets the roof to seal air leaks.
- 2). Build a damn around the existing flue pipe or chimney with aluminum flashing. Measure the size of the chimney or flue pipe and cut aluminum flashing 6 to 8 inches larger than the flue pipe or chimney with metal shears to create a sleeve. Check all local codes to determine the exact size of the insulation damn. Generally, codes require a 1- to 2-inch damn around metal flue pipes and 3 to 4 inches around a masonry chimney. Building a damn prevents insulation from coming in direct contact with a hot flue pipe or chimney.
- 3). Cut the aluminum flashing at the bottom and top of the every 2 inches all around, and each cut will measure 3 inches deep in order to create tabs on the aluminum sleeve.
- 4). Grasp each cut on the bottom with vice grips and pull up to form a 90-degree angle.
- 5). Grasp the tabs on the top and fold them in to create a 90-angle.
- 6). Place the sleeve around the chimney or flue pipe and staple the tabs into the attic floor with a heavy-duty stapler. The top-folded tabs will keep the sleeve sitting back from the flue pipe or chimney the appropriate distance.
- 7). Seal the seam on the sleeve with furnace cement.
- 8). Place insulation without a paper backing, known as unfaced insulation, around the damn.
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