Bought a Harman P38 used locally and it came with a whole direct vent exhaust. Have a 8" hole in chimney I'm trying to adapt to but the Duravent is the only type I can find an adapter for and it won't fit the type I have which I believe is made by ICC Chimney/ExcelDirect pipe which has a rubber sealer on the inside. Does anyone know if they make an adapter to go from this 3" ExcelDirect pipe to 8" chimney?