Heat riser, weight issues, and other questions

I have read so much today about RMH designs that my head is swimming and I'm starting to get overwhelmed with the details! Help! I need to do some brain picking. I have a few questions that have likely been answered already, but for some reason many of the threads have been kicking me off into 404 error land today. Forgive me if there's some repetition here.

My first question is about the heat riser. Is there any reason not to use a section of triple walled stove pipe for this? I have a lovely section about 4 feet long sitting on my porch, going unused.

My second question is about the issue of WEIGHT and all that cob. Our floor is suspended on joists, with laminate flooring in the area that I want to install the RMH. I read in Ianto's book that a typical RMH requires 3-4000(!) pounds of cob material! YIKES! Not possible without a major shoring up of the floor structures. Will do it if necessary, but 4,000 pounds of mass seems like a bit of overkill to me. Our home is only 900 square feet, super-insulated, and we layer up on clothes if we're chilly, rather than heating the whole house to 75 degrees. We also block our 100 sq foot pantry off for the winter, insulate around the door, and leave it unheated, so effectively we only need to heat 800 sq. feet of house.

I have seen a few ideas float by about portable RMH's, like Paul Wheaton's design, as well as ideas about lighter materials to fill the bench. I like the look of cob, stone, and such for the bench, but I also like the idea of not having to pour cement footers in my crawl space to keep my floor from collapsing. Is there a way to build a bench that can be cushioned and sat/slept on, that will have good enough mass, and that will also be light enough to be supported by floor joists? And any guesses as to how much Paul Wheaton's portable, wood-framed, design weighs?

All input is greatly appreciated. I'm a total noob.

Lauren Dixon : First some good news, yes you can use that Triple wall pipe to make a heat riser out of, If you used the term triple wall generically, and what you have is
actually an insulated Stanless Steel insulated pipe even better !

Have you been to Permies.com(s) sister site richsoil.com to click on 'Rocket stoves', and watched to whole series !? You can trust these videos - Not like the Dreck
on You-tube!

Have you gone to cobcottage.com to get your PDF Copy $15.oo of Evans' and Jackson's Book 'Rocket Mass Heaters', there is STILL No other book in any
Language with more Rocket Stove, Pocket Rocket, And Rocket Mass Heater family information ! ( and I don't make a dime ! )

If you have a pre-50's house, or a house built '' to code " after the mid 70's you should be o.k. for weight. The Mid Seventies is when builders caught up with the waterbed
craze! Before 1950, they still were building good houses generally! There is a Section in "The book' that discusses how to brace a floor if there is a question in your mind,
please read and understand well enough to explain to a second person the part about insulating your floor from the direct heat of you potential Rocket Mass Heater R.M.H.!

After you have your copy of 'The Book' you can decide if you are truly serious about a Rocket Mass Heater in your future ! While you will have very little trouble creating a
R.M.H. out doors as a trial to prove to yourself that you can do a R.M.H., a good Thermal Mass bench is where you store the heat energy to heat your house for 24 hrs at a
time. Paul W.s portable thermal mass benches are a less than perfect compromise that might be alright for a winter but should be a stopgap that is planned for replacement
with a conventional Thermal mass bench that will allow you to use more of the heat energy provided by your R.M.H. !( and use even less wood !) Hope this helps !

For the Good of the Craft ! As always your Questions / comments are solicited and Welcome ! Think like Fire ! flow like a Gas,Don't be the Marshmallow ! BIG AL !

Allen,

Thanks for your reply. Yep, I have a copy of "The Book" and have been tearing through it over the last couple of days. Also, I have watched the videos on richsoil.com about 5 times each. I feel that I have a pretty good basic understanding of the RMH's function, and the pros and cons of using one as a main heat source. I don't, however, feel at all confident about slapping one together in my house! Of course, we will build a mock-up in the yard first, to make sure we're on the right track, but I still have major doubts about my abilities. Doubting my abilities is a pattern for me, reaching far beyond the issue of building an RMH! But, that's a discussion for a different forum...

Our house was built in 1980, BUT, we live in an area with ZERO building codes. This can be nice in some circumstances, but leaves some doubt about certain aspects of our house (i.e. our roof was built halfway with engineered trusses, and halfway with cobbled together 2x6's). However, that being said, our floor joists are of the proper size, with a spacing that seems standard (will measure spacing today). With this is mind, how much weight can our floor realistically take? I have looked at some RMH designs, such as the 8" cabin RMH plans that E&E are selling, which looks like it can't contain much more than 800 lbs. of material. Maybe I'm way off-base with that estimate? Even 800 lbs seems like a pretty major constant load to put on a floor. I once saw a 1200 lb. horse ridden into a bar with joist floors, and the floor was seriously bowing under the weight, so that the rider felt he needed a contingency bail-over-the-bar plan should the floor fall through. HA! The floor held, but just barely! Now, I'm thinking about a horse-sized mass sitting permanently along one side of the room, and envisioning a slow, but steady sinking floor with a $10,000 repair bill.

I am completely committed to this project, so it's not a question of 'if'. At this point, I am needing technical help and some cheer-leading, more than anything. I'm not a good self-starter, and find it difficult to wade into a project without having EVERY LAST DETAIL firmly understood. I appreciate the help.

Alright, we took some measurements and our floor joists are 2x8 with 24" spacing and 13' spans. The joists themselves are 26' long intersected by a 2x8 beam running dead-center down the length of the house, with a 12x6 beam under it, also running the length of the house, which is set on cement footings spaced about 12' apart. Now I'm thinking, after a good look, that we could probably set our RMH bench lined up right on top of that large center beam, and use the RMH bench as a sort of half-wall divider between our living room and kitchen. If we set it right on top of that beam, would that eliminate all weight concerns?

Lauren Dixon : Paul Wheaton Is planing two workshops on Lightweight/Portable R.M.H.s This fall, I and my wife have separately and together volunteered to show up before
other events, and worked to help the Host get ready for a scheduled workshop for ether a reduced price, or Free !

It is very important that you and the host agree as to what your duties are, when they start, and when They End ! You should have very limited and clearly defined duties
during the Workshop itself !

The weight issue is important, But! I personally have a Friend who swears that a waterbed is good for a bad back, and is now on his third waterbed after the 2nd catastrophic
failure of a King size waterbed. The water drained down thru the Floor via the Hot and Cold Forced Air Floor registers and the new one was in place the same day !

Total time on the floor of his downstairs bedroom is - unknown, but over 23 years- I just asked ! There is No visible difference between the houses bedroom and Living room !

Its floor rafters are ruff cut 3x8s on 14'' centers with a finished tongue and grove over ruff 5/4 pine planking ! "The Book" will give you all the info on reinforcement you will
need !

My next R.M.H. build will go into a 20' Yurt, and the center floor will be cob over a small cement pour ! but thats a different story ! I Like the 8'' Cabin design though !

E and E have a Great guide that can be used as a check sheet by going to their site, and going through their event planning section to reach their Site Planning Guide. It stands
alone as a great Checklist for your D.I.Y. / R.M.H. Project ! I hope this helps, come back here often, with over 18,000 members there will always be someone here who wants
to talk about what you want to talk about ! For the good of the Craft !

As always questions /comments are solicited and are welcome. Think Like Fire, Flow like a Gas, Don't be the Marshmallow ! PYRO - Logically, BIG AL !

Thanks for the reference to the site planning guide. I consulted a structural engineer about my project, and he gave me the go-ahead to load 1,000 lbs. on top of that floor support beam without concern. Any more than that, and a simple insertion of an extra pillar under the beam is all we need. So, looks like we're good to go! Hooray!

Your Floor sounds similar to mine this is what I did to support all that weight, I only had room for 2 tons.

RMH on wooden floor...