Yiannis : You are going to heat treat the first meter of your galvanized stove pipe, around here stove pipe comes 30 inches long or 3/4 of a meter, you will have
to heat treat two sections, to have 1 meter of piping.
It will be different for you if you go with 1/2 barrels, you will need less pipe. I have not built with '1/2 barrels' myself, I will watch and learn if you build that way !
I also do not use ductwork, relying on the thermal mass to heat my living space, I live very close to the Canadian Border !
You will still need galvanized stove pipe to help create the manifold that channels the vertically falling hot exhaust gases from the barrel turning them 90 degrees
to flow into the horizontal Run of pipe or barrels in your Cob Thermal Mass Bench !
You need to remeasure the areas of your house you want heated, 6'' is too small for your Pergola, and 1st and second floors, however, you must find out what sizes
you can get locally for materials!
If you do not remove the paint and oils from the barrel before - you will be breathing them while tending the Rocket Mass
Heaters RMH Fire!
Please consider going to
rocketstoves.com, to download a PDF Copy $18.ooUS, of the brand new 3rd addition of
'Rocket Mass Heaters'. With ~100,000~
built word wide most of them have been made following 'The Book' and 95% of all the first builds (That Worked ) were made following 'The Book'
Feel free to check with "max'' on 'The Book' and I do not make a penny off of Recommending "The Book'' !
I do not know what is available to you for fire brick, you must do the finding on your end, go talk to a potter/ceramist !
If you had a junk motor, it would be worth something as salvage, heavy dense rocks are free !
Ideally to hold the most amount of heat within your thermal mass, the pipes should be deep within the mass, I have no problems with their way !
Ideally you should plan on doing a little every day, 10 cm -15 cm deep is enough to finish in a day, you want the pipes to be covered with 5cm -8 cm of Cob First,
before adding your other Heavy Dense materials !
You can take small green branches, 2cm-4cm, as long as possible the ends are stuck into the soft cob, and then the Green branches are woven together rather
like basket making, and then covered with more Cob Look up'' Wattle-and-Daub'', this makes a permanent back on your bench, and allows you to have warm air
circulating around your bench and not heating an outside wall !
Think like Fire, flow like a Gas, Don't be the Marshmallow ! As always your comments, and questions, are Solicited and Welcome! PYRO - Logically Big AL
Late note : you are going to want several clean outs , I can not tell until we have settled on a design, plan for your construction Good luck ! A. L.