Introducing the FlueSnug 5 - this all-in-one seal for boiler flues has been designed to fit a 5" cored hole, ensuring an airtight and professional finish. Using the FS5 is a quicker, cheaper and cleaner way to seal a hole around a flue. It's perfect for like-for-like boiler swaps - with no need to re-core, fitting the FlueSnug saves significant time, effort and cost. This 100mm flue fitting complies with Part L Building Regulations, and is approved by major boiler manufacturers including Baxi, Worcester Bosch, Ideal Heat and ATAG. Replaces need to mortar around flue. No need to re-core. Approved by major boiler manufacturers. Internal and external use. Fits 127mm/5″ core-drilled hole. Manufactured to the highest standards, including ISO9001 (Quality Management) and ISO14001 (Environmental Management). Complies with Part L Building Regulations. Designed to fit 100mm boiler flues.