only a chimney sweep working to NACS code of prctice can tell you this as he or she will be issuing you with a 12month certificate.As well as regular sweeping of your chimney burning good quality Kiln Dried Logs,Eco briquettes and Ecoal are essential so as not to damage your fire.Build up of unburnt splinters of wood and tarring of your chimney from damp poor seasoned logs or especially unseasoned can cause chimney fires.Build up of residue on the top plate of your wood burner needs to be removed frequently another good reason for cleaning your chimney.You can buy only quality fuels at Fitch Fuels just go online at www.fitchrecycling.co.uk or for a Clean Sweep go to www.c2sut.co.uk  Graham covers all of Manchester