Several variables need to be considered to determine the proper size of a venting system. These include, but are not limited to, air supply, connector type, BTU input of the appliance, lateral offset and height of the vent system. To assist you in designing a proper system, download our "Gas Vent, Chimney Sizing & Application Guide (6 MB, PDF)". This guide covers single and multiple appliance venting and proper chimney sizing. It has a complete set of easy-to-use sizing tables, the same tables used in the National Fuel Gas Code. Included in the guide are common definitions, examples, tips on what you should and should not do and many illustrations to help you along the way.