I want to build a RMH in my plantship (see: https://permies.com/t/27725/green-building/types-eco-buildings).
The thing is, that the passage through the wall is build with diameter 13 cm which is about 5".
Now I think about building a 6" RMH with 6m of 6" pipe in a 6m clay bench and than a 5" pipe up and out.
Because the air in the pipe will be cooled so the air will be shrunken (right word?) So I think that the last part could be 5" pipes.
Konstantin Kirsch : Build your system the way you want to, come up from the end of your thermal mass still in 6'' and make the 6'' to 5'' reducer part of the thimble-
(sometimes called a Jack west of the Mississippi, here in the U.S.A.)
then use your 5'' system for the rest.
You may not have any problem at all, I would havea plan to replace the horizontal 5'' thimble with a 6'' thimble just in case ! Good Luck ! For the good of the craft !
Think like fire, flow like gas, Don't be the Marshmallow !As always, comments and questions are solicited and all Welcome ! PYRO - Logically, BIG AL !
Success has a Thousand Fathers , Failure is an Orphan