I am kind of new at looking at all the plans online and possible materials that can be used for constructing an efficient and top end RMH, but am interested in the best possible construction when it is time for me to place a RMH in my workshop at home. Instead of using a metal based or brick based riser has anyone experimented with the ceramic chimney liners? The insulation and temperature resistant properties of that material seems to me like it would be a superior material for the feed tube, burn tunnel and the heat riser. The liners are durable and come in square and round applications in both 6" and 8" diameters. Just wondering if it has been tried yet, there have been way too many posts to wander aimlessly through to find an answer, I only have so much time to do my research. Any information would be greatly appreciated.

D. Smith :Welcome to Permies, And congratulations and a Big Welcome to the "rocket stove' Forum Threads ! You will long remember your First post here !

Yes! Using ceramic tile as a liner in the 'Heat Risers/internal chimneys' of RMHs has been done. Generally there is a net gain to be found when replacing both
a thick, heavy metal chimney, or even most forms of Building Brick!

However we must quickly cover the major differences between these two types and include refractory materials ! please excuse a little history lessen !

When rocket mass heaters were created out of the wood-fired Cooking Stoves that came first, they were of course Experimental and at first the goal was to build strong
enough, and durable enough to survive the High Temperatures found within the 'Heat Riser / Internal Chimney' !

Today we are mostly building with refractory materials that are more insulating than just Ceramic tile! While able to also 'handle the High Temperatures' it is made of
such dense material* that it absorbs enough of the Initial Heat to slow down the creation of the High Heat environment and its remarkable High efficiencies !

Using Perlite bound with just enough clay slip, and held within the 'Sacrificial Form' walls of light weight metal to create a highly insulating 'Heat Riser' as compared with
Ceramic materials, we reach a steady state high temp environment and its high efficiencies with less smoke sooner and over all !

Tomorrows improvements ARE in development today, and this is the point where All your Fellow Permies members are at! Again let me say Welcome To Permies and Rocket
Mass Heaters !

Please take this as a strong recommendation from a 'been there done that' member. You can save yourself the time that is important to you, and to all your fellow members
and go to 'rocket stoves.com' for your PDF copy $15.oo of Evans' and Jackson's Great book Rocket Mass Heaters' There is Still no other source of 'rocket stove Family'
information in one place,in any language (and I don't make a dime !)

For the Craft, For the Future ! Be safe, Keep Warm ! PYRO Logical Big AL - As always, All Questions / Comments are solicited and are Welcome ! A. L.

*Clay, Generally its all clay, the best is called 'fire clay' mostly Not because of its ability to take high heat but because it expands less so that it IS more able to take high heat
without cracking - if this interests you look up grog - Big AL

I do indeed have the book that you have referenced and it has helped out tremendously, but at this point in time I have not had a chance to really give building even a mock RMH a go. I would have not skipped on the additional Perlite/clay insulation and used the chimney ceramic just in place of the metal. But if it is going to impede the initial heat it looks like I will not be using ceramic now.

What is the best possible material to use in making the heat riser? I only ask out of pure curiosity, because when I build my own I want to make it out of the best recommended materials at the time of the build. Would a double walled flue for a traditional stove work? I see that there are so many ways that this can go, and I really want to make the most out of the efficiency.

D. Smith : I am only able to advise you on what is possible here, having vicariously helped on many builds in different places, I find that materials that are easily available
here are sometimes hard to find locally sourced and prohibitive if it needs to be Transported !

You Will need to find out what might be available for high Temperature refractory materials in your area, you may be able to score some of the very lightweight pumice that
actually floats !

For my next R.M.H., I will be heating a small area and will use 6'' thru out ! Tthe interior wall of my heat riser will be a sacrificial form made from a lightweight piece of blued
steel cold air round pipe, the outside wall will be approximately 20'' in diameter, and heavier because i will be using the 'metal skin' off of a hot water tank, the interior space
will be stuffed with perlite that is Generally man made to equal a high grade of volcanic pellets also known by that name, mixed with locally sourced clay made into a 'clay slip'
-to make a rigid, highly durable material Even after the interior pipe in my heat riser fails, I expect the perlite clay clip heat riser to continue to work for years.

With rapid advancements in research and an ever growing number of people wanting high end refractory materials to build ever more efficient R.M.H.s, I expect to have my
pick of an affordable 'cast refractory heat rise'r and other parts with in 5 yrs ! For the good of the craft ! Big Al

Good info, Allen but the question remains - what has proven to be the most durable and efficient (and preferably affordable and workable) material for constructing the heat riser? I travel quite a bit for work and really don't want to get the "honey the rocket stove is acting funny" phone call when I'm in outer East Overshoe and can't get home for 4 days then make it home to an IBC of frozen fish and a very angry wife

Dave Jersey : the terms given were 'Proven' and 'durable and efficient' Most durable would be a 7X7 square Heat Riser Made out of fire brick, laid in a running bond,
and wrapped with additional insulation to fill out the space between the outside of the Heat Riser and the barrel the show proper respect, and to keep constant the
Cross Sectional Areas / C.S.A.s Wholey !

The set up proven most efficient would be exactly as I described above, please re-read my words so you can understand my high degree of satisfaction with the way
I have plained My next build !

For the Good Of The Craft ! Be safe, keep warm ! PYRO-LOGICALLY Big AL ! - As always, your questions / comments are solicited and Welcome ! - A. L.

Thank you for further clarification Al. This is all helping very much. I am sure there will be many more questions I have for people such as you with the hands on experience and the technical know how.

Now would the additional insulation be the Perlite/clay mixture held in place by formed sheet metal such as stainless steel, to have the ideal spacing for the heat exchange barrel to the exhaust? As an example for a 8" combustion chamber I would need to maintain the 2 inch clearance from the top of the heat riser to the barrel surface and the 1.5 inch side clearance from the insulation barrier to the walls of the barrel? As seen by example on page 23 of the RMH book you referenced in the prior post.

D. Smith : Generally Yes !, Yes !,Yes!, And Yes ! When the hot exhaust gases leave the bottom of the barrel they enter the transitional area
where they are channeled and turned horizontally 90 degrees into a wide sweeping turn with gentle corners past walls finished to a smooth
surface like sheet rock. Then passing over a generous, Deep Ash pit, and are funneled down to the 8'' Cross Sectional Area as the Hot
gases are swept out straight out past the horizontal clean out ! More follows Big Al !

D. Smith : It is possible to set the barrel slightly off center to the Heat Riser / Internal Chimney ! This is done to protect the exposures on one side of the barrel,
creating a cooler-safer side, and a sui-side Sorry ! (NOT)

If and when this option is taken, the location of the Transitional area to receive the hot exhaust gases should be directly under that wider side ! Other than the
Generally approved idea that the Cross Sectional Areas / C.S.A.s, top and barrel sides is a minimum that can be exceeded but never cut back from, I try to
keep to that plan ! For the Good of the Craft ! Be safe, keep warm ! pyro - logical Big Al - Your Questions/comments are solicited and are Welcome ! A. L. !

I have see examples of the offsetting of the barrel. Nifty idea, but in my build I plan on keeping it traditionally centered just for simplicity because it is going to be my first RMH. To create a buffer from the barrel I was thinking about creating a brick based open barrier to enclose the barrel and also serve as a small thermal battery (Personally I think the plain barrel could use some churching up) about 4 inches away from the walls to catch and hold onto some of that precious radiated heat, and not inhibit the flow of heat to the rest of the room.

D. Smith : Works for me, I believe in conservative builds, especially on first builds Under the category of - if the world hands you lemons - if you get bricks with holes
in them, Think about using metal rods to help secure a lattice of bricks without other fasteners it beats the hell out of playing 52 pick-up with bricks ! Big AL

D. Smith and Dave J. : Can I send you both to Creighton S.s Forum Thread ' Water glass ' this does not change my answer - It adds to it , and to your fund
of useful information ! For the Craft ! be safe, keep warm ! PYRO-LOGICAL - Big AL ! - As always, Comments/Questions are solicited and are Welcome ! A. L.