I have an application where I need to provide exhaust for two gas-fired chillers. The discharge temp. is a constant 1400 deg. The problem is the connection to chiller, expansion joints, catalytic converter, ect. supplied with the chiller are all based on 4"ID. Thus far, I have not been able to locate a supplier that makes pre-fab material w/ a 4"ID for this discharge temp. Furthermore, I do not want to use 5"-6"ID and use transitional fittings as this seems like it would disrupt draft. Termination at roof is about 105L.F. rise - no exhausto fans are being used. When all is said and done it appears I will be forced to use SS pipe to meet diameter requirements, unless anybody knows of a manufacturer than can meet these requirements.