Rocket Mass Heater built in to wood shop slab floor

I am building a wood shop, and about to pour the slab foundation. I was thinking about building the insulated fire box and exhaust pipe into the slab to use it to absorb the heat. The barrel would set in to the slab. Any thoughts on if this is workable? What diameter pipe? OK to just pour concrete around the duct pipe? The duct pipe would probably be about a 16' linear run from the barrel to the exterior, exiting at grade, on a hill side, so a straight shot out. I was thinking a 6" pipe to on the exhaust side. Would love to here the groups thoughts on how to make it work. My hope is to use scrap wood to fire the stove, and the concrete slab to store the heat. The slab is 10' x 16'. The pipe would run down the center long ways.

Thanks!

jay

Jay : A 6''Rocket Mass Heater system can do most of what you want, however the RMH will have a keyhole shaped foot print of nearly 4' X 6'!

Within this space No Concrete made from portland cement is safe from total distraction due to the Wickedly high Combustion temperatures !

After that we can couple the RMHs thermal mass with the concrete. I would recommend ether insulating under the slab or insulating the
perimeter of the slab down below the frost line, and a good Vapor barrier in ether case!

Speaking about frost line it would be a good idea to know your location and climate type !

While you did not mention an Exterior Vertical chimney, You will Need one. It can be connected to the horizontal stove pipe at the end of your
concrete slab with a dog house structure built over it, and should be mounted to the downwind side of the the Workshop! IF the Workshop is
built onto an existing structure like your house, you should plan on Your final vertical chimney needing to go over the peak of the roof by 4'
then try it with less and add on as needed!

This will be difficult build, more so than a Big Bench style Thermal Mass, which you are thinking of as lost space right now, we will work on that.

For the Good of the craft! Big AL

Hello Jay,

You project and goals sound interesting and generally very achievable. I would suggest have a read through some of the information in this link about Ondol:

온돌 (Ondol) An ancient original form of heating with wood...

Hi Allen,

All and all I agree with some of your advice and recommendations. Much of it can enhance and or extend the live of a system. Some however is speculative and/or subjective. As a few examples "vapor barriers" are new inventions and not necessary at all for proper and efficient function. Neither is a chimneys that must go past roof ridges. Much of what we "think we know" about fire places, furnaces and the related are based as much on habitual concepts in construction as they are actual "wood combustion understanding and realities." If many of the describe "have to and musts" of building wood burning combustion chambers were true...the Ondol and related radiant floor heating systems of the last 4000 years would not have worked...

Just another view shared...

Regards,

j

Below, please find just a few examples of thousands of types of 굴뚝 (chimney) used with these types of systems...

Jay C. White Cloud : I'm being hung with old rope.I will modify my position on vapor barriers under concrete slabs to say that If there are any suspected drainage
issues they should be addressed first, Next I would roughly level the site and haul in crusher run Gravel to raise the base of my pour above grade , and then belt
and suspenders, add a vapor barrier, in this case the Hydrophilic properties of concrete are well known, but specifically in this case an elevated base and a vapor
barrier would tend to promote a dryer soil due to the creation of an Umbrella effect, reducing loss of heat energy and adding insulation.

I was guilty of flagrant laziness and hurry in not being specific in my intent ! I agree that vapor barriers have ruined to many houses tone cavalier about recom-
mending them!

I most often tell everyone to plan on a final vertical chimney that exceeds the minimum of breaking the plan of the roof, I have seen detached chimneys work
well in more than one location often superiorly ones that were sited in june disregarding unknown weather conditions in Jan Feb,

I will pick my battles carefully with regard to chimney height! But do want to point out that your portfolio of photographs are likely to favor builds who know how
to site and build chimneys in harmony with local weather patterns !

You'll love this one I have even seen SIP Panels fail do to a heavy machinery type accident and they had been in place for 7 years and interiorly were like new !

For the good of the Crafts, ALL of them ! Big AL

Jay : I wanted to look up a specific picture to show you the core of the foot print we/You will be working within the Center of your wood shop!

At the top of this thread where it says Permies >> Forums >> energy >> rocket stoves click on rocket stoves, this will take you

to a new rocket stove Threads page, you will find near the top of the page :::-->

rocket mass heater shippable core clickon and then at that thread scroll down to Emily Aaston's Thread Extensions for Nov 10th 2013,

you are looking for the picture labeled Finishing the manifold with an inside lip

The inside lip is where the open end of the 55gallon drum sits ! For our/Your purposes visualize just the large tire thing and the square box feed
tube at its front,

Installed at the center of your Wood shop this model would still need to be packed in insulation and a 1st Shell of Cob, and a 2nd layer of
structural cob need to surround everything , fortunately the RMH Shippable core is slightly oversize here and represents the finished size of your
rmh with final shell on it ! Mostly ! For the Good of the Craft ! Big AL

Jay C. White Cloud wrote:Hello Jay,

You project and goals sound interesting and generally very achievable. I would suggest have a read through some of the information in this link about Ondol:

Thanks Jay. And thanks Allen.

Yes, I remember traveling in Korea and seeing similar technique for warming floors from fire beside and beneath and circulating through. I am wondering if the exhaust pipe should be something like clay pipe to the outside, rather than galvanized. Maybe surrounded by some perlite tapered to nothing as it goes from the fire toward the exit. Seems like the firebox and such could be firebrick that the cement would be poured around. Then some cob to set the drum down on.

Hi Allen...

I wrote my entire section above more as...he, he, ha, ha,...which you got...you're great that way Brother!!!

I love the "...I'm being hung with old rope..." comment. I haven't heard that since one of my old (really old...born in 1877) teachers used it...thanks for that memory...

I will modify my position on vapor barriers under concrete slabs to say that If there are any suspected drainage issues they should be addressed first, Next I would roughly level the site and haul in crusher run Gravel to raise the base of my pour above grade , and then belt and suspenders, add a vapor barrier, in this case the Hydrophilic properties of concrete are well known, but specifically in this case an elevated base and a vapor barrier would tend to promote a dryer soil due to the creation of an Umbrella effect, reducing loss of heat energy and adding insulation.

EXCELLENT, EXCELLENT, excellent

This segues into a point I kinda wanted to make but didn't really have a chance to...thanks for the opening Al. I have seen built, and have built several garages and workshops that use no concrete at all. As Brother Allen knows...I do not like concrete, the industry behind it, nor what it does environmentally to this planet each year, but that is another topic. We do not have to use concrete, nor does it even proven that great a surface to stand and work on. Wooden covered bridges do not have concrete floors, barns do not have concrete floors and I was in one this past week built in 1786 that houses an entire tractor collection and workshop...Guess what!!!....All slab wood floors over 150 years old and older...

One could easily build a raised gravel podii, then more stone for another area that would house a RMH unit to heat the shop/garage.

I just have to put that out there since this is a "permaculture forum" and not a "mainstream" methods promoting place...Just food for thought..

I most often tell everyone to plan on a final vertical chimney that exceeds the minimum of breaking the plan of the roof, I have seen detached chimneys work
well in more than one location often superiorly ones that were sited in june disregarding unknown weather conditions in Jan Feb,

One of the questions I originally had with the Ondol design was the loss of heating mass that was contained inside the chimney...Why put it outside...Yet later learned that this was not a great loss do to the very low exit temps of these wood heaters. Now I have seen some places where they build a small outbuilding that contains the chimney and it warms this space to some degree or is the support for another chimney that is use in summer cooking or smoking of foods. All in all, it is a very old and good system.

I will pick my battles carefully with regard to chimney height! But do want to point out that your portfolio of photographs are likely to favor builds who know how
to site and build chimneys in harmony with local weather patterns !

I agree with that 100%...

What I would add is that if a unit has exhaust gases that are over 150 degrees then a centralized chimney, within the thermal envelope of the architecture is the best use of this thermal mass and extra heat. It the exhaust gases from a wood burning unit is much lower, then chimney location is of less critical and turns towards functional placement and primary wind directions to remove what smoke there is away from ingress and egress paths. Or, as mentioned above, perhaps another use for the exterior chimney architecture to be employed as support for some other function, e.g. smoke house, wood shed, drying shed, summer kitchen, etc.

As usual Big Al...great stuff comes from or talks...!

Warm Regards,

j