Midtherm HTS Twin Wall Flue - Removable Starter LengthThe length is manufactured with a 0. 9mm inner and a clean out door with test point that can be removed to allow access to the inner door. This product is to be used when the provision of sweeping through the appliance is not available and to allow the stove to be moved after installation. It can also be installed to retrofit a stove when HT S is already installed in situ. The Midtherm HTS Twinwall 1000mm Length is a single length of twin wall pipe