How to Cut a Stainless Steel Flexible Chimney Liner
July 19, 2023
Proper Tools for Cutting the Flexible Liner
When installing a new chimney liner, most likely you will need to cut your liner to the correct size. This is a job you can handle with proper preparation.
A good pair of gloves and safety glasses are essential; the liner will be sharp! If cutting it on the ground, wrap duct tape around the cut end for your safety.
The best tool to use, for the quickest and cleanest cut, is a grinder with an abrasive metal cut off wheel. Circular saws with metal cutting blades will also do a great job. A Sawzall (reciprocating saw) with a metal blade will work, but it does vibrate and the finish cuts aren't always the prettiest; but when everything is attached, the cut end of the liner is not visible anyway. Of course, a new blade in a hack saw, or a pair of heavy duty metal snips, will get it done too.
You'll need to decide on whether to cut the liner before or after the installation, as there are advantages and disadvantages to both options.
Cutting the Flexible Liner
If you plan on cutting it before installing, you will be able to work more comfortably. Cutting it on the ground it allows for stable footing and extra hands if needed. But you will need VERY accurate measurements for the total length. Make sure to add 3 inches above the top of the chimney for the top plate collar that secures the liner. Once you are sure of your measurements, mark the liner. I suggest wrapping a piece of duct tape or masking tape at that mark to ensure a straighter cut. DO NOT try to follow one of the seams on a flexible liner while cutting, you could end up 3 inches off by the time you get all the way around!
If you plan on cutting the liner after the installation (my preference), the collar on the top plate gives you a good reference point for a straight cut. Everything will be connected and there will be no doubt if you will have enough liner. Make sure you have a long enough extension cord, if you are going to need one, and if you are working from a ladder, do not try to over reach.
The amount of liner left above the top plate collar should be at a minimum. There should be at least 5 inches of space between the end of the liner and the chimney cap lid for proper ventilation.
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