We're designing a rocket stove for our house with a mass heater bench and bench-back built of cob and brick (we have lots of free brick from craigslist). The house is made of wooden stud construction, so we have left the barrel and burn tunnel 1.5' from any wood walls with insulation, shiny aluminum foil, and an air space behind it. I'd love feedback on the design, if you have some. This will be my first build, though I helped with one (mostly the cobbing, though). Not obvious in the drawing is the fact that we plan to surround the bottom 1/2 of the barrel with bricks (less radiant heat, but a little more child-proof) as well as 1/3 of the sides and the entire back that faces toward the wall. We would also put more insulation around the combustion chamber on the back side facing the wall, allowing most of the radiant heat to go in to the room.
Some feedback I already got was that we probably don't need so man twists and turns for the exhaust snaking through the brick/ cob wall. It goes back and forth 3 times each with the hope that it will be nice and cool by the time it reaches the top of the wall where it has less thermal mass between the pipes and the stud wall, but if fewer runs will work, and would leave more room for thermal mass, we can go that route too.
Some specific questions I have are what kind of radius do we need for the turns in order to keep a good draught. Also, would you recommend adding a pilot hole somewhere near the flue/ chimney to help create draught to such the smoke up before everything is really heated up so we don't have smoke back? If so, where would you put it?
Also, we plan to store adjacent next to feed barrel and wonder how much insulation or thermal mass we need separating the wood from the barrel so that the wood is nicely dried out but doesn't catch fire.
Noelle : you can offset the barrel slightly off center from your Heat Riser 2 - 21/2 '' the side with more area at the bottom where it sits on the bricks will be the hotter side with the tight side cooler , this will also make your exhaust plumbing - where it goes from the bottom of the barrel and twists 90 degrees sideways easier to make with a Cross Sectional Area , C.S.A. equal to the C.S.A. of your heat riser ! You are limited to the radius of the stove pipe you can get though you can get stainless steel flex smoke pipe to run inside older chimneys that would make a more gentle curve- it is pricey and i've never used it !
I would never recommend a pilot hole it will work against you and spoil your draft/draw. If you need to, you can remove the last clean out where your horizontal stove pipe turns into your vertical chimney ( one 'Tee" with a clean -out for every level of your pipe) And ether burn a twist of newspaper to warm the chimney or as a last resort place a small fan in the 'Tee' replacing the cap for a forced air draft as a last resort. You might be able to pick up a 12 volt one at a
car scrap yard that will work off of a car battery !
Generally you want your plumbing as centralized as possible and trying a layout that you like with your water services closer to the center of the house should be a consideration,again this is your house and i am outside my area of experience, do as you will Pyro Al
Success has a Thousand Fathers , Failure is an Orphan