Before every installation, you must have your chimney swept by an approved chimney sweep using the NACS website. They will come to your home and sweep the chimney, followed by a integrity test (remember to ask for this). They will then issue a certificate of sweeping confirming the chimney is safe to use or if it needs lining. If it needs lining this is because smoke is leaking out of the flue. This could be through the breached midfeathers and into the adjacent flue, in the same stack. Or, it could be leaking through the masonry into a bedroom, loft space or out of the pointing at the top of the stack. Please see our chimney lining services for different options for lining.