Cindy our sauna heaters work with a standard 6" sauna stove pipe. For the inside you can use regular single wall black stove pipe. For added safety you can also use double wall which will not be as hot on the outer surface. You will need to purchase a through wall kit for the chimney where it exists the sauna. The outside sauna pipe shoudl be approved stainless steel piping with a rain cap and spark arrestor on the top. The higher up your chimney goes the better it will be for creating a proper draft. I sugest at least 6'.
The sauna stoves also have both side chimneys and a top chimney with a spcial cap plug to plug the chimney port that you are not using.