Pipes and knees, made of 2mm thick steel sheet, have been designed for extracting combustion gases from wood-fired devices to chimney ducts, acc. to DIN 18 160 and ISO 4736. Based on tests made in the Kerosene and Gas Institute in Kraków, Poland, in the range of fire-resistance in temperature of 1000°C, the product has been technologically approved and is permitted to be sold and used.