Sealing a Flue in an Attic With Metal

Inspect the flue piping to ensure there is at least 1 inch of clearance on all sides around the piping. This includes making sure insulation is kept at least 1 inch away due to heat output.

Measure the width of the space between the two beams on either side of the flue pipe and cut a piece of metal flashing to this width with the metal cutters. Make sure to cut a curve in one side to allow it to fit snugly around the pipe.

Fit the flashing in place on the floor of the attic so it lays flush against the flue pipe on the side with the gap, covering the gap. If there are wood beams or drywall underneath, use a few nails to hold the flashing in place. You can also use staples.

Caulk around the entire section of the flashing piece with high-temperature caulk. Caulk where the pipe meets the flashing.

Cut another piece of flashing that is long enough to wrap around the flue pipe. Cut slits into the bottom of the flashing piece to make it easier to bend the flashing flat on the bottom. Use a rubber mallet to shape the flashing so a small portion lays flat on the drywall at the base of the pipe and wrap the flashing tightly around the pipe.

Caulk around the entire edge of the flashing with high-temperature caulking. Use staples or small nails to hold down the bottom of the flashing. Do not nail or staple into the flue pipe, only the drywall or beam around it.