How to Seal With Wall Thimbles


A wall thimble serves as the housing for a stove flue or chimney as it passes through a wall. The device prevents the heat of the stovepipe from dissipating to the wall where it could pose a fire hazard. The unit is commonly made of two segments that are mounted from either side of the wall and fastened in place with wood screws or bolts. Proper installation can improve the function of the thimble by preventing fire and sealing the opening from drafts.

Things You'll Need

  • Wall thimble
  • Screwdriver
  • Silicone Caulk
  • Heat-proof culk
  • Cut away the outside siding to fit the flange of the thimble rather than the required opening. The opening is commonly round while the flange is square. By trimming away the siding, which often is beveled, you create a flat surface for attaching the thimble flange.

  • Fit the sections of the thimble into the wall opening from each side. Make sure both flanges fit flat against the wall surface. Fasten the flanges tightly in place by using the included screws. The thimble needs to fit securely. Any movement in the thimble will make it difficult to maintain a seal between the thimble and the wall.

  • Apply silicone caulk to the seams between the thimble and both sides of the wall.

  • Place the stovepipe through the opening of the thimble. Apply high temperature caulk at the junctions between the stovepipe and the thimble.

Tips & Warnings

  • Make sure the thimble fits the wall and stovepipe. Thimbles may be specific to the wall width and the diameter of the stovepipe. Always use wall thimbles certified for the type of stove using the flue.
  • Improper installation of a wall thimble can lead to a fire hazard for the home. If you have any concern about your abilities to perform these functions properly, hire a professional stove installer.

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