A twin wall flue system typically costs between £800 and £2,000 depending on the height required, the number of bends, and whether it runs internally or externally up the outside of the property. Twin wall flues are commonly used where a property has no existing masonry chimney, offering a compliant route to safely vent a stove through a wall or roof. Material costs form part of the overall price, but professional installation is essential to ensure the correct clearances and weatherproofing are achieved. Always get a fixed quote for the full twin wall flue installation rather than relying on material costs alone.