How to Install a Chimney Thimble

What You'll Need
Chimney kit
High temperature cement
Silicone caulk
Margin trowel

An important part of chimney installation is the chimney thimble. In most cases, this is a piece of metal that fits into the hole where the chimney will exit your wall. This is used when connecting something like a wood stove to a chimney. Chimney thimbles come in a variety of thickness. Choosing a thick chimney thimble will provide a better fit when you are installing your chimney pipe. Because the chimney thimble must be cemented in using a high temperature cement, the installation of the thimble is best done during the installation of the remainder of the chimney.  

Step 1 - Measure Your Hole 

After determining where the chimney will exit the wall, you will need to cut a hole that measures the diameter of your chimney. After you cut your hole, measure to determine how large of a chimney thimble you will need to install. Keep in mind that chimney thimbles come in varying thicknesses so choose one that works best for your project.  

Step 2 - Prepare the Cement 

When installing a chimney thimble with your chimney , you will need to use a high temperature cement on the outside of the thimble. Prepare your cement per the instructions on the bag. Using a trowel mix the cement with water in bucket. Check with your local home improvement store for a ready mix cement or one that will dry faster.

Step 3 - Installation 

After preparing your cement, place a layer of cement on the outside of the thimble. This is the part that is touching the wall. Using a high temperature cement to install your chimney thimble will help protect your wall from heat damage. You will not need to place any cement on the inside of the thimble. Let the cement dry for about 24 hours.

Once your cement is dry, run a layer of silicone base caulk around the diameter to make sure any gaps are filled in and ensure a good fit. Insert the chimney pipe into the thimble. You will not need to use any cement or caulk to do this.

Your chimney kit may have screws that you can use to attach the thimble to the wall. It is okay to use those, however, most building codes will require that you use a high temperature cement in addition to the masonry screws to insure proper and safe installation.

Step 4 - Finish Installing Your Chimney 

After you have your thimble in place you are ready to continue installation on the remainder of your chimney. Attach the recommended amount of horizontal chimney to the clean out tee. Insert this through your wall and into the house. Keep in mind that per fire safety guidelines, the chimney must extend into the room at least 4 inches. Run your flue between the stove and chimney and attach with screws.