rocket stove in a yurt: safety and other questions

Hey permies,

I'm moving into a 20' yurt, and currently building a rocket stove / RMH, and I have two main questions: is it overkill, and how do I make it safe?

A bit about the heater: 6" C vent pipe throughout, 18" riser inside a 55gal steel drum, 8" pipe on the riser and the gap is filled with compressed vermiculite (no clay).

From the barrel the pipe goes into a 4' long bench filled with (from the ground up) cement board, vermiculite, and river stones, loops back around, then goes up an 8' chimney and exits the yurt through the roof.

Under the barrel I'm planning on putting cement board and bricks, and behind it between the barrel and the lattice, more cement board.

I'm hesitant to encase the barrel in cob for a two reasons: clay is inaccessible (the yurt is way up a mountain, making clay impractical to transport, and no clay is readily available on site), and I may need to take the yurt down at some point in the next few years for one reason or another, and the cob would make that impractical.

Is the heater likely to be safe in the configuration I've described?

The second question I have is, maybe this is overkill for heating a 314sqft space? The walls are insulated with aerofoil, and the floor is insulated with 3" foam board enclosed in plastic.

Your expertise and experience are appreciated, thanks.

Bob : You're living my dream ! Seriously, once again the land deal fell through-

Lets try to move your story a little bit closer to its happy ending ! As I understand you, you do have a few problems !

6'' pipe, good! I cant recommend going any smaller, and never on a 1st build ! The length of the Heat Riser should be 2Xs the length of the Burn Tunnel
and 3Xs the length of the Feed Tube! so you are a little on the short side, we want All the combustion done by the top of the heat riser/barrel interface.
After that your barrel should radiate off enough heat to cool and condense the hot exhaust Gases causing them to fall!

It sounds like you are using a piece of 6'' cold air return duct as the inside form of your Heat Riser, and an 8'' piece of pipe as the outside form of your
Heat Riser (?) Couple of problems there ! Both of these pipe pieces should be considered as sacrificial forms that theHot exhaust gases (2000+dF) will
quickly consume! With no Clay mixed in with Your vermiculite you will not have a rigid heat riser form left and it will fail !

While I have drank the cool-aide and accept Perlight as a slightly better product than vermiculite, ether could be used mixed with clay bought at Lowes
or Home Depot (80#s Lincoln 60 fire clay) to make a rigid self supporting heat riser but you need to find or make an 12'' diameter container/shell for
the outside wall of your heat riser creating a wall thickness of 3'' 12 - 6 = 6, two 3'' thick walls = 6, 6 + 6 = 12 this is partly to replace the insulating
ability lost by mixing your insulation with clay ! Yes this may increase the size of your barrel !

Your bench is a little small and the vermiculite is not needed here at all ! The air spaces between the stones will be slightly insulating ( though not as -
-much as using sand - many more individual airspaces )
Earlier you said 6'' (cold air return pipe? ) throughout and then you mentioned an 8'' chimney (!) The size should remain standard through out ! Did you
mean 6'' insulated stove pipe ? as long as you assemble the correct hardware its outside diameter is not important !

I am a little concerned that you will have to use an insulated final vertical chimney as you may not be Transferring enough heat to your thermal mass
and cooling the Temperature of the exhaust gases down to ~ 150dF that we would like to see and could be safely vented through the roof in your Yurt.

Under Your Rocket mass heater every where i would start out with a layer of Aluminum foil shiny side up and glued to the floor, a pattern of bricks to
make air channels cement board with an other layer of alum foil shiny side up, an outside shell layer of brick set on edge and 3'' high filled with P' lite
and clay or V'lite and clay with a few bricks in for support and then start laying fire brick for my Rocket Mass Heater RMH !

Aero foil insulation is a Two edged sword, as promised by the guy who sold you on it, it WILL reflect 80+ percent* of all the Radiant Heat that
is radiating from your thermal mass ! Its R-value or its ability to Resist conducting heat through itself is a very low R-19, this was a minimum
standard set in the early 70s This means as your Thermal mass cools down and there is less radiant energy, your Yurt will instantly feel cool ! This
is another good reason to maximize the heat storage ability of your thermal mass the idea here is not to fill up your Yurt with RMH, but to have a fine
piece of well crafted built in furniture that seems to increase the amount of room within your Yurt !

I have to do a little research to give you links to smooth your understanding of the points I am making please be sure that you are at the right place all
these looming problems WILL shrink to mole hills with further explanation ! For the Craft ! Big AL

Rob McT. : A late Welcome to Permies.com, our sister site Richsoil.com and the Rocket and Wood stove forum threads ! You have not
shared a location, as you mention being up a hill/mountain an elevation and whether you have full or part sun and morning or evening sun will help
us give you advice good for your location.

Who knows, by putting yourself out there you may find a near neighbor with Rocket Mass Heater or Cob Experience !

O. K., standard disclaimer, There is a lot of Crap out there on U-tube, verify (if you can everything you see there !)

I am sending you to a set of video clips making up most of a for sale DVD showing how to set up your Rocket mass Heater on Flammable flooring !

Goto -> Villagevideo.org, Find and click-on the You-Tube Icon, at the next (You-Tube page) scroll down to a series of video clips labeled -

Rocket Mass Heater Scenes, and use your mouse to cover the area immediately to that word phrases right ! the words play > will appear -

Click on this and set back and enjoy the first part of a professionally done video, showing serious professionals walking you through the first several
parts of an up-scale Rocket Mass Heater Build - House modification (your will be easier !) If you like craftsmanship there is lots of eye candy !

Near the Top left of this page find the Permies >> forums >> energy >> rocket stoves line and click on rocket stoves . This will take you to
the lists of ALL rocket mass heater/stove Forum Threads. Most recent ones listed 1st ! Find and click on

video: great rocket mass heaters in upstate n.y. and Quebec - The 1st video is about living with a RMH, and though her system is an 8" RMH
in upstate New York, she can heat 3Xs the space from her Rocket, your 6'' will probably do you jest fine ( your location is ? unknown )

Please consider going he the My Profile Button found in our Permies Toolbox near the top right of this page and enter the information you feel
comfortable with ! Membership has its privileges, besides the ~27,000~ fellow members You have the Toolbox with a search function that you will
quickly learn to use giving you 24 / 7 access to the 10s of thousands of past Permies Threads.

Again though you will need to change a few design plans your willingness to think outside the box is very valued here - '' Without change, there is
NO Progress " For the good of the Crafts !

Think like Fire! Flow Like a Gas! Don't be the Marshmallow! As always, your questions comments are welcome and solicited ! Big AL

Al! Thank you sir, for the in depth answer. I've added a few pictures for clarity.

I now wish I'd done more research on the heat riser before building, as mine is cemented together and proved impossible to disassemble... Oh well, I suppose I'll have to build another.

The yurt is about one hour outside of Vancouver, BC.

In terms of having a 6" ID and 12" OD = 3" clay and verm gap on the heat riser, this sounds good to me, my question is, where might I find caps for the top and bottom? At least in my location, those kinds of transitions are both hard to find and excessively expensive. My very simple system cost over $500, and that was after shopping around at 4 different stores. The 6" to 8" cap was the only one they carried, and those alone cost me over $100. The local stores don't even carry 12" C vent, only 6" and 8". Your advice for sourcing materials is appreciated.

I am also concerned that the system won't have enough length to sufficiently dissipate the heat before exiting the yurt; hopefully this won't be the case, as insulated pipe is $125 per 18" locally.

Bob McT. : The good news is that you can think outside the box ! The bad news is you are too far out there. Stop, we are going to re-boot this whole thing.

Next thing I want you to do is to take a total inventory of what you have, with a separate listing for Something you have damaged ! We will now plan on
building on the cheap to get you heat for this winter safely even if you re-build in the spring

The First thing I want you to do Now when you get this, is to go to cobcottage.com to download your $18.00 U.S. Copy of Rocket Mass Heaters
With over 100,000 Rocket mass heater built this is 'The Book' almost al of the RMHs in the world have been made from this book, and 95% of the first timers
builds (that worked ) were made from this book ! There is only a little middle-school science and less math all 4th grade-ish ! With this book you can come
back here to your fellow members at permies and know that you can talk the talk and understand the RMHs size, shapes, and orientation of the parts to each
other and themselves !

Later we will list in order safe rmh videos made while professional builders made rockets, or under the direction of pros ! I promise that if you just hang in with
me and learn how to make just one J-tube rocket mass Heater we will make it fun, after you have used an Rmh to heat your Yurt for a Heating season then
you can try to reinvent the wheel ! for the good of the Craft ! Big AL