47The vent pipe may pass through unconditioned areas. The amountof exposed pipe allowed is shown in Table 14.1. Using winter design temperature (used in load calculations),find appropriate temperature for your application and fur-nace model.2. Determine the amount of total and exposed vent pipe.3. Determine required insulation thickness for exposed pipelength(s).4. When combustion air inlet piping is installed above a sus-pended ceiling, the pipe MUST be insulated with moistureresistant insulation such as Armaflex or other equivalenttype of insulation.5. Insulate combustion air inlet piping when run in warm, hu-mid spaces.6. Install the insulation per the insulation manufacturer’s in-stallation instructions.NOTE: Pipe length (ft. / M) specified for maximum pipe lengthslocated in unconditioned spaces cannot exceed total allowable pipelength as calculated from Table 15 or 17.Configure the FurnaceCARBON MONOXIDE POISONING HAZARDFailure to follow this warning could result in personalinjury or death.To route the vent pipe and combustion air pipe through thefurnace, the manufacturer supplied kit must be used. Failureto properly seal the blower compartment from the furnacevestibule could result in the circulation of carbon monoxidethroughout the structure. The vent pipe and combustion airpipe must be a continuous pipe while passing through theblower compartment. Seals supplied in this kit must beinstalled per the instructions provided. Follow allprocedures outlined in these instructions.WARNING!Install the Vent and Combustion Air PipesWith the furnace installed in the required position, remove thedesired knockouts from the casing. It will be necessary to removeone knockout for the vent pipe and the other knockout for thecombustion air connection. See Fig. 12.Use a flat blade screwdriver and tap on the knockout on oppositesides, where the knockout meets the casing. Fold the knockoutdown with duct pliers and work the knockout back and forth untilit is removed. Trim any excess metal from the knockout with tinsnips.The vent elbow can be rotated to the required location on thecasing if necessary. See Fig. 38. To rotate the vent elbow:1. Loosen the clamp on the inlet of the vent elbow attached tothe inducer.2. Rotate the vent elbow to the required position. There arerounded notches on the vent elbow to align it with theinducer housing for each orientation.3. Tighten the clamp around the vent elbow. Torque the clampto 15 lb--in. See Fig. 40--43.Installing the Vent Pipe Adapter and Combustion AirPipe AdapterCARBON MONOXIDE POISONING HAZARDFailure to follow this warning could result in personalinjury or death.To route the vent pipe and combustion air pipe through thefurnace, the manufacturer supplied kit must be used. Failureto properly seal the blower compartment from the furnacevestibule could result in the circulation of carbon monoxidethroughout the structure. The vent pipe and combustion airpipe must be a continuous pipe while passing through theblower compartment. Seals supplied in this kit must beinstalled per the instructions provided. Follow allprocedures outlined in these instructions.WARNING!CARBON MONOXIDE POISONING HAZARDFailure to follow this warning could result in personal injuryor death.DO NOT use cement to join polypropylene venting systems.Follow the polypropylene venting system manufacturer’sinstructions for installing polypropylene venting systems.! WARNINGNOTE: The rubber coupling that attaches to the vent pipe adaptermust be used. The adapter seals the vent pipe to the casing andreduces the strain on the vent elbow attached to the inducer.1. Apply the gaskets to the vent pipe and combustion air pipeadapters. If supplied, remove and discard round center“slug” from interior of gasket. See Fig. 37.NOTE: The vent pipe adapter can be distinguished from the inletpipe adapter by the absence of an internal pipe--stopping ring. Thevent pipe can pass through the vent pipe adapter; it cannot passthrough the inlet pipe adapter.2. Align the screw holes in the plastic vent pipe adapter withthe dimples in the casing.3. Pilot drill the screw holes for the adapter in the casing andattach the vent pipe adapter to the furnace with sheet metalscrews4. Slide the end of the rubber vent coupling with notches in itover the standoffs on the vent pipe adapter.5. Insert a length of vent pipe through the coupling into theoutlet of the vent elbow.6. Tighten the clamp around the outlet of the vent elbow.Torque the clamp to 15 lb--in.The following instructions are for PVC/ABS DWV ventpiping only. DO NOT USE THESE TECHNIQUES FORPOLYPROPYLENE VENT PIPING SYSTEMS. See thepolypropylene vent system manufacturer’s instructions forinstalling polypropylene venting systems.NOTICEInstall the remaining vent and combustion air pipes as shownbelow. It is recommended that all pipes be cut, prepared, andpre--assembled before permanently cementing any joint.1. Working from furnace to outside, cut pipe to requiredlength(s).2. De--burr inside and outside of pipe.59TP6A