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Question regarding space between insulation and drum

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Greetings from Australia

I.m building a stove with 6" riser and a smaller drum due to space limitations but i'm not sure if
due to the smaller surface area of the drum, whether I need to
adjust the outside diameter of the insulating cylinder around the heat riser to get the correct "draw".
My understanding was that it should be around 1 1/2' gap. Am I on the right track?

By the way I was thinking of cutting and welding 2 drums to get the height needed.
Any thoughts before I start would be appreciated.

Thanks in advance to everyone on the forum-this is my first post.
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Location: +52° 1' 47.40", +4° 22' 57.80"
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Hi Justin, welcome to the boards.

The side gap, between insulation canister and barrel, should be at least 1.5". These stoves has the tendency to run better with wider gaps. Even the top gap could be as large as 3' without a problem at all. Beware of the transition from the barrel to the bench, this is many times the culprit when the stove refuse to burn properly. Make this ridiculously wide, it will spare you the trouble of restriction hunting. And go for a proper chimney stack, reaching above the highest point of the roof.
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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Justin G. : Have you been to 'Rocketstoves.com' to download your PDF copy $15.ooU.S. of Ianto Evans' great book "Rocket Mass Heaters" (I don't make a nickel)
There is no other source of Rocket Stove information in any language with more information!

Its interesting that you have decided to go with a smaller barrel. Because we have to radiate a certain amount of heat of of the barrel to create the push that drives
the exhaust gas horizontally thru our thermal mass, we have to be aware of the Physics that demands that the smaller barrel must radiate the same amount of heat
as the Larger barrel, most radiate the same amount of heat at a higher temperature! This is what makes a cuddle with your 3 year old so pleasant when they want to
"climb up'' in your lap. Due to the smaller surface area to mass ratio they radiate this heat energy at a slightly higher temp ! A radiator in your lap!

You should consider the 1 1/2'' figure to be a minimum to guarantee that you keep the correct 'Cross Sectional Area' thru-out your build. You can set the drum slight-
-ly offset or Eccentric to the Heat Riser, pinching or narrowing the riser insulation to sidewall of the barrel Gap to decrease the heat radiated off of that side of the
barrel protecting exposures on that side, the other side will radiate more heat and have a more active gas flow. It should be located just above the transition space
carrying the hot exhaust gases horizontally out of the base of your Rocket Stove into your thermal mass.

This transition space should be a well insulated space with smooth walls, generously funneling the gases down to this horizontal exit, and also providing a ash pit and
directly after a clean out with a tightly sealed cap!

For the good of the Craft, be safe, keep warm, PYROmagically Big AL
There's a way to do it better - find it. -Edison. A better tiny ad:
Rocket Mass Heater Plans - now free for a while
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