The Concentric Vent allows both the intake for combustion air and the exhaust vent to pass through a standard roof or sidewall. This is an alternative to the standard two pipe intake/vent shown in the basic furnace installation instructions. CVENT-3 is for use with 3 in. intake/vent systems. Refer to the furnace installation instructions for intake/vent pipe sizing information. WARNING Do not use the Concentric Vent kit for anything other than a Category IV furnace. Failure to follow this warning could result in fire, personal injury or death. WARNING Do not operate the furnace until the installation and assembly of the Concentric Vent and all piping are completed. Failure to follow this warning could result in product damage or improper operation, personal injury or death. NOTE: The Concentric Vent reduces the allowable intake/vent piping length by 5 ft. from that listed in the basic furnace installation instructions.