When you see your chimney sweep you can ask them to estimate the required size for your chimney liner and it is then possible to get custom chimney liners built to fit the specific size of your chimney and this will of course be the closest thing you can get to a guarantee that your chimney liner will fit.

These custom shapes may be rectangle, circular, oval, square etc and in general you will be charged for your chimney liner by the square foot. You can expect the product to be about 25-40 foot and this will of course depend on the size of your chimney. Whether you have oval chimney liners, or other shaped chimney liners will depend on the size and shape of your chimney. Alternatively using flexible chimney liner kits it may be possible to alter the size and shape of your chimney lining yourself. This then means that you can use flexible chimney liner kits in order to ensure that what you get is the right size and shape for your chimney.