Oil & Gas Boilers & Hot Water Heaters Utilize Chimneys To Vent Dangerous Exhaust Gasses Out Of The Home. Oil Boilers Create Soot That Builds Up In The Chimney And Causes Blockages & Puffbacks. Gas While Much Cleaner Burning Creates Moisture In The Flue, Often Causing Damage To The Internal Clay Tiles In A Masonry Chimney. Gas Flues Should Be Swept & Inspected Every 2 Years