rocket stove cookstove hybrid

hello dear permies.com community!

i'm from austria and eager to build my first rmh that will be placed in my yet to build sunroom
therefore i wanted to convert a existing stove i have (for convenience of being able to cook and bake with it) into a rocket stove hybrid (for more efficiency and mass heat a bench)
since all rmh gurus are on permies.com - so i've heard - i wanted to kindly ask for your review and suggestion on my plan (i want to figure out if it will draft well enough with my current design)
the current stove looks kind of like this: (not my own - just for reference) http://thumbs1.picclick.com/d/w1600/pict/172291489812_/Tirolia-K%C3%BCchenherd-Herd-Ofen-Holzofen-Holzofenherd-Beistellherd.jpg


i have attached a picture of my current design which i want to integrate and replace the burn and ash chamber of the current stove with

some dimensions of the drawing:
feed opening:
10x12cm = 3.937x4.724in
burn "chamber" diameter:
10x12cm = 3.937x4.724in
burn "chamber" length:
27cm = 10.629in (till front)
15cm = 5.905in (till outer heat riser)
heat riser diameter:
10x12cm = 3.937x4.724in
heat riser length:
33cm = 12.992in
top plate distance to cooking plate:
3cm = 1.181in
exhaust circle diameter
12cm = 4.724in

the chamber and riser will be built out of 3cm = 1.181in thick vermiculite plates
the stove has a drawer beneath it - i could still go a bit deeper if absolutely needed (but prefer not to)
love to hear your thoughts!

kind regards,
dominik

PS: i know that the ratio isn't 1:2:3 or even 1:2:4 BUT
i thought since it will be well insulated and i have two doors:
i could use the ash door to create a L tube to get it started (also convenient for cleanout)
and once it burns and has enough draft i can close it and switch to the upper door to create a J feeding tube OR i can load fuel vertically through the upper door close it again and keep the lower door open for air intake

Welcome to permies, Dominic!

We can't tell how it will draft without knowing more about your chimney and the flue path to reach it. This is a very small unit you are describing, and it may work fine for cooking, but will probably not have enough heat output or draft strength to charge a storage mass. What is the size and character of your dwelling structure?

Is your proposed feed at the lower left door panel? It seems to be somewhat of an L-tube or possibly J-tube you are proposing. You would get more heat from a batch box for a given system size. Have you seen Satamax's range retrofit?
You will likely be better off building a separate heater for space heating.

Glenn Herbert wrote:Welcome to permies, Dominic!

thank you! pleasure to be here!

Glenn Herbert wrote:We can't tell how it will draft without knowing more about your chimney and the flue path to reach it. This is a very small unit you are describing, and it may work fine for cooking, but will probably not have enough heat output or draft strength to charge a storage mass. What is the size and character of your dwelling structure?

it will be placed in a small sunroom facing east 2,5x3,5x2m = 8x11,5x6,6ft that also acts as a fly brake in front of my tiny one-room house which is like 5x5x4m =~16x16x13ft (drawing attached)
aside from being able to cook with it it should also warm a slim bench that is 2x1x0,45m = 6,6x3,2x1,47ft and maybe the triangular space under the roof (where my night bed is) - the whole house would be even better
the stove should go two lengths through the bench/bed and then go up a through a smoke tube through the highest edge of the sunroom which is like 2,5m = 8,2ft measured from floor level and go up for another 1m=3,2ft or so

Glenn Herbert wrote:Is your proposed feed at the lower left door panel? It seems to be somewhat of an L-tube or possibly J-tube you are proposing.

thats right, i edited my original post, pasting it here aswell:
PS: i know that the ratio isn't 1:2:3 or even 1:2:4 BUT
i thought since it will be well insulated and i have two doors:
i could use the ash door to create a L tube to get it started (also convenient for cleanout)
and once it burns and has enough draft i can close it and switch to the upper door to create a J feeding tube OR i can load fuel vertically through the upper door close it again and keep the lower door open for air intake - should/could that work?

Glenn Herbert wrote:You would get more heat from a batch box for a given system size. Have you seen Satamax's range retrofit?
You will likely be better off building a separate heater for space heating.

my space is very limited so i try to combine it
what chamber diameter would you suggest for that space? all i can get out of the stove like in that batch design? space under the cooking surface is 28x50x41,5cm =~ 11x20x16ft should that be enough? (kind of nice btw - haven't seen it before)
i prefer the j-tube though - i like the gravity feed design

i would go for barrelbuild but it gets so tall (following the proven design - i would need a stool to cook on top) and i'm not sure if the top will be hot enough to cook wok menues and that kind of stuff, will it? -
also i would miss the baking oven -
so i still want to find a way to build a working hybrid - themed the quote hope dies last

thanks for your thoughts so far!

As your house is so small a heater the size you describe might be able to heat it, depending on how well insulated it is and how cold and cloudy your winter gets. A sunroom with glass roof as your sketch seems to show would lose a lot of heat, though. There would probably not be enough heat left after warming the cooktop and bench to warm the main space. Also, even if the sunroom were well insulated, having the heat source in there would diminish the warmth that reaches the main space.

A 6" J-tube with a short burn tunnel and no front ash door is still easy to reach and clean out by hand - even easier if you make a small scoop like a sardine can - I have done it myself. If you make the floor of the burn tunnel at the bottom of the lower door, you should have enough height for a decent heat riser. The top of the feed tube would then be about level with the top of the bottom door.

What size is the existing exhaust from the stove? Do you have a chimney already, or will you be buying new stovepipe? If new, I think 6"/15cm would be smart, for the most heat capacity.

Considering all the bends and constrictions in the stove, I think it would be good to minimize the friction in the bench, so I would propose a half-barrel bell instead of ducts winding through the bench.

By the way, what is the floor structure? Is it slab on grade, or wood framing? You will need a lot of weight for the mass bench.

Hi, I haven't been here for a while, everything has changed.  I would like to post a new question, but can't figure out how.  I am looking at a hybrid, but wondering about burning coal in a rocket stove.  

Go to the Rocket Mass Heaters subforum and find the "New Topic" button at the top right of the main content box.

Dominik, check range rocket retrofit.

Satamax Antone wrote:Dominik, check range rocket retrofit.

https://permies.com/t/35569/Range-retrofit

Tho, i would do some things differently now.