Rocket mass heater

Hi. We are looking to puta rocket mass heater in our hempcrete home.  We live in northern Ontario and have cold winters, we managed this past winter with a small stove and uninsulated floor, bedrock.  And we were warm.  This year we are putting in earthen floors and adding a mud room on the back of the home.  Our question is why is it not advised to feed the rocket mass heater from a different room than the burn chamber bell?   Ideally we feel feeding the heater from the mud room addition will keep wood storage out of main area and any potential backdraft out of living space.  Our walls are 12” thick. We have the chimney exit already for an 8” rocket mass design.  Other than monitoring issues with fire bing in a different room is there any reason not to put the j through the wall. Hempcrete does not burn, and has some thermal mass
Thanks
Kristin

Hi Kristin;
Welcome to Permies and Welcome to Rocket science!

Yes , absolutely in your case you can have a feed tube in the mud room and your barrel and mass in the other.
Popping into your mud room every 45-60 minutes to feed the dragon will be no big deal.

My only concern would be your burn tunnel length.    You cannot extend that burn tunnel roof beyond 10- 12" or so.
If you do, here's what  will happen.
Your stove will work great!   Dragon roaring, lots of heat , easy starting!

Part way thru winter your stove will seem sluggish....
Soon it will start acting up....
When you open up your cleanout ports you will find your pipes are more than 1/2 way plugged...

I speak from experience here.
I thought it would be fine to have a long tunnel... (apx 15")
Turns out  its a very bad idea.  I learned all about doing a rebuild during a northern Montana winter... it can be done.
That J tube was in our uninsulated greenhouse/studio. I did a rebuild in about 3-4 hrs that day!
Much easier/less stressful  to do a rebuild on a warm spring day!

So, if you follow build sizing parameter's closely and don't be like me and "modify them" you will be fine!

Tell us more  (with pictures please) about your plans  and about your home itself.

Thinking about this... (oh no)
With a 12" wall you will need to thin that out  substantially for a J tube to fit.
Only at your core, the rest would remain 12" thick.
To keep the barrel in your living space, your feed tube needs to be inset from the mud room side to stay within J tube size parameter's.
This leaves more room in the mud room for storage.

Effectively, you would hack out an archway in the mud room side of your wall that is tall enough to easily feed wood into the J-tube. With a noncombustible wall, the barrel around the riser can almost touch the wall, so you would have the feed opening sticking a couple inches out from the mud room face of the wall. Add 6" or so for core structure around the feed, and the RMH would only stick out 8-10" into the mud room space.

ThAnk you for feedback.  We have decided to keep the feed inside we would have had to extend the burn tunnel slightly and appreciate feedback that that is not ideal. So I guess I will be trying to cob in shelves for wood storage to try to contain all the mess of wood inside the living space but I have seen a few fun ideas.  Thank you