Flexible chimney liner system design, internal dimensions of the chimney

We need an idea of the narrowest internal dimensions of your chimney. You will have to estimate these measurements to the best of your abilities. Use a torch and look up into the chimney. The reason we need these measurements is to work out which type of insulation would best suit your needs. If the chimney is quite small then rockwool sleevs will be too big to go down, especially if there are and bends in your chimney.