Here at Ash Chimney Sweeps our specialty is cleaning fireplaces, wood stoves and their chimneys, in addition to chimneys for furnace's. The entire process takes approximately 45 minutes to an hour and is completely GUARANTEED MESS FREE. Gas Furnace Chimneys These units typically DO NOT require sweeping, but may need to be cleaned if large deposits are present due to a malfunction or if animals have nested.The cleaning procedure is similar to a wood stove cleaning. Oil Furnace Chimneys Cleaning is generally required every 2 to 4 years depending on the number of appliances and usage or if a blockage has occurred (i.e., animal nesting). The cleaning procedure is similar to a wood stove cleaning. A regular exam is also recommend.