NOTE: Central Boiler sizes chimneys by their insidediameter. A 6" chimney has a 6" inside diameter and an 8"outside diameter. An 8" chimney has an 8" inside diameter and a10" outside diameter. A 10" chimney has a 10" insidediameter and a 12" outside diameter. When ordering a chimney partfor a Central Boiler furnace, be sure to use the Central Boiler designated chimneysize when ordering rather than the actual measurement. For example, whenordering a chimney cap for a Classic 6048, even though the actual outsidediameter is 10”, order the 8” chimney cap. If you do not know the propersize for chimney parts, please call first. All returns for incorrectlyordered parts drop shipped from Central Boiler will incur return shipping and a20% restocking fee.