1st RMH BUILD -- old house in detroit, scrappy approach, win

[mrgregcrawford]

I have posted a duplicate thread over at permies.com -- hoping to net a few unique replies from each forum.

I've got a big (2,700 sq ft), old (built in 1903) house, in a relatively dense neighborhood in Detroit, Michigan. Our house is entirely off-grid (no city water -- all caught; no sewer -- all composted; no electrics -- off-grid solar-system)... and winter is coming! The house is only insulated in the attic, above the 3rd floor -- I know, I know. I just don't have time this season.

Our intent is to have the RMH integrate (as) seamlessly (as possible) with the existing structure/layout -- which is a challenge of trade-offs. We will be 'shrinking' the living-area (bedroom, kitchen, living room, composting toilet) from 2,700 sq ft down to 3 or maybe 4 standard-size rooms. I am hopeful that a RMH with an 8" system throughout can provide enough heat to cut the cold. Please correct me if I am mistaken. We have an existing, 2-sided fireplace, which is south-facing, centrally located East to West, and 5ft from the front doors. This chimney is 35-40ft tall, and includes 4 flues, one of which is lined (though it isn't the easiest to pipe into). The plan is to build the core and bell, out of re-purposed firebrick + 55g metal drum, on one side of the chimney, and then pipe the ducting (including manifold) though the brick wall separating the two fireplaces, where a 48" x 85" mass of urbanite, brick, earth, etc. will be positioned. This will be our (wife and I's) winter-bed. Directing the piping is a tiny challenge, as its entrance arrives at the longer-angled axis of the mass... so even distribution of heat to mass is a touch tricky, but enough drawing should solve this easily enough. We will be laying 6 cinder-block columns in the basement for additional support below the mass. Existing concrete slab has minor damage in a single 1' x 1' area, which I do not believe to be of significant concern, post-patch job. I am considering laying a column or two under the combustion unit as well, but I haven't committed to that yet.

If all this seems prudent to you, and I'm on the right track, I would like to ask what I came to ask: can I pipe the exhaust (which has travelled 50ft, incl. 5ft per elbow, through the mass material) down/vertically about 5ft into the basement, where one final bend will take it outside, to and through a small garden bed, which will, it is most hoped, become warm(er) than it would otherwise be. Even if the exhaust is 65 degrees f... this is substantially warmer than the outdoor winter temp. The wind comes from this direction, so that appears to be a plus. But, is it possible/feasible to drop the pipe's run by several feet and take it another 15-20ft outside, all in a horizontal run? Boy oh boy, does a year-round growing-bed sound mighty tasty... Or: do you recommend that I just pipe it into the existing, and most welcoming 35ft chimney, thereby increasing draft, ejecting all so safely away?

I am probably forgetting to ask some other outstandingly important things... but, yes.

Thank you so many millions in advance! I will be laying the support columns tomorrow. Soon to be rounding up materials. Excited to hear from you all.
greg

[matthewwalker]

Use the chimney. You might consider an easier layout and two separate systems for that much uninsulated space.

[mrgregcrawford]

thanks for the quick reply matthewwalker.

having two separate systems would assist with the enormous chimney mass... which i am a little concerned about being a hungry heat-sink. I may have to insulate/plaster the chimney, worst-case.

are you suggesting that each of the two systems exist on either side of the chimney, at each fireplace? interesting idea. annoying that i need to support such weight down in the basement -- that would be the design challenge.

[satamax]

Greg, check this donkey32.proboards.com/thread/1274/rocket-heater-fireplace-design

Please read it all and check the result.

donkey32.proboards.com/post/13115/thread

Please post pics at permies. Of what you have. May be the multiple flues can be used as bells, and you could be missing the details to do it.

[mrgregcrawford]

thanks max! quite an ingenious design, i like the creativity. saves on space too.

though, it appears that cooking with this RMH style is impossible... or, at least not incredibly user-friendly. and my RMH will (hopefully) be our primary cooking source. I also want that quick heat which the metal barrel bell can provide.

the idea i have is to pass the piping, just after the manifold from the bell, through the dividing-wall which separates the two fireplaces, and into the mass material which will be located on the other side/around the 2nd fireplace.

i will get some photos up ASAP.

thanks again!

[matthewwalker]

Sept 29, 2014 9:10:26 GMT -8 mrgregcrawford said:

are you suggesting that each of the two systems exist on either side of the chimney, at each fireplace?

I hadn't really thought about the details, other than you've got a lot of space to heat and these are relatively small btu heaters. They work best if you are in the room with them, so two seems to make sense in your application where you have space and chimneys. I'd probably consider lower mass or spread the mass out and try to avoid having to build too much infrastructure. Just some overall thoughts that might lead you down some paths you hadn't considered.

[satamax]

donkey32.proboards.com/thread/1216/new-range-candidate-rocket-retrofit

[DCish]

FYI for photos, the space here is full. You'll have to post elsewhere, then link to them here so they show up. Also, how about a burner and barrel, then both existing chimneys as bells (sized, of course, to not overload your burner)? Seems a shame to not use existing mass and spend the energy to add more. Of course, this may not be a workable solution once I see the pics... Looking forward to the pics!

[satamax]

Greg, for fuck sake!

Please transform that into a rocket massonry heater!






Check this: www.permies.com/t/31382/a/13852/chimneybell.skp?download_attachment=true

You replace the top of the bell extension in front of the chimney by a cast iron plate from a range, and you can cook on it!




Myself, i would do two sides. One with a batch rocket in the fireplace as JRL did. And make a range retrofit exhaust into the bell of the batch rocket. Not the safest option, may be. But i'd love that design.

[Daryl]

Aw sh*t, it's beautiful.

(ignore me)

[mrgregcrawford]

photos can be found here: www.permies.com/t/39914/rocket-stoves/st-RMH-BUILD-house-detroit

about this rocket masonry heater... i like the idea of heating up the chimney mass, this is quite certainly desirable, as i am slightly concerned that it will otherwise be a bit of a thermal nosebleed, being enormous, as well as connected to the outdoor temps. i see myself missing the heated bed-platform, as my intent was to heat our bodies, most directly, as opposed to heating the space (for the first year). one could build a bed up on the top there...

the range retrofit is most sexy.

there must be baffles -- bricks built in courses -- within the unit displayed in the image you posted above? i would avoid masonry-skilling, in deference to earthen ones.

unfortunately, a ticking is tocking quite loudly in my brain. i absolutely must begin permanently setting materials in the coming couple of days. love the original thinking. i will read what you have suggested, and consider it.

[DCish]

No baffles. A bell is an open space where hot gasses rise and cooler gasses fall. The exhaust vent is located as low as possible so the coolest "spent" gasses go up the chimney. In the case of this chimney, you would plug the fireplace at some point up the chimney (sheet metal insulated with ceramic blanket would do) where the internal surface area is ideal (not more than 6 sq meters not counting the floor for a 6" batch box) and run a flue through the plug down to a few inches above the bottom of the sealed fireplace. You set up a rocket burner (batch box or j-tube) that vents into the sealed fireplace. The hot gasses rise to the plug where they transfer heat to the walls of the fireplace/chimney until they cool and fall to the bottom. Since the exhaust flue (insulate it!) draws gasses from the floor of the chamber, where they are the coolest, you get a highly efficient and very simple way to harvest heat with minimal construction. Heck, you could do this as a quick and simple project to give you some heat while you make your lovely heated bed... The link that satamax gave describes one version of this that worked quite well, lots of details there, a compact, effective build, but by no means the only way you could do it (for example, you could brick or cob the fireplace front closed rather than use metal, have the burner outside with barrel for radiant heat, then send the gasses into the bell. Requires little floor reinforcing if any at all because you are using the existing mass).

[satamax]

The good auld plunger tube

Your concern about it being a heatsink is right, but, heat travels into solids in all directions, not only up. And, the longer travel to the outside takes longer, so your heat has a chance to be dissipated somewhere else in the house before. And you're not loosing all, but half of it. Then with the plug, you're keeping the hot gases on the bottom of the chimney. Plus, you can always insulate it upstairs or on the roof, to slow down the heat transfer to the great outsides. I'm prety sure it will be hotter at the bottom, due to the bell effect. As well, considering the amount of work you save, you could go to do something else, insulation wise. Myself, all i have in my new place is 8x8 chimeys, two of thoses. No doors, no slab, no stairs! You bet i would love to have something like yours! As well, it's near in the ideal spot, in the middle of the house!

[mrgregcrawford]

the exhaust flue is insulated with a ceramic blanket as well?
and, an 8" batch box would then deserve a plugged surface area of no more than 8 sq meters?

would it be possible to do both? that is, plug the chimney to slow/make the most use of the warm(er) air exiting from the mass material of the RMH? or, is the temp. diff. not wide enough? i suppose i can expect an exhaust temp somewhere between 90-120... the longer i can keep that heat in contact with my mass materials, the better. i do perk at the possibility of making quick heat. and i think that the rocket masonry heater is more appropriate for a few reasons, and yet, my major hangup is:

i most definitely think it wise to heat a horizontal platform of mass. sitting/laying upon the heat appears to be the most effective & direct (not to mention comfortable) way to receive constant doses of heat to the body. if the two designs can be unified somehow, this is a real winner; or, at minimum, if a heated platform can be integrated with the masonry heater.

thanks fellas. now i feel like i am yielding some fruit from the forums.

[mrgregcrawford]

three questions:

*at what temperature (or temperature differential) does steam/smoke choose to fall, rather than rise?
*any guesstimate for what kind of temperatures the exhaust would be, once exiting the house via the chimney?
*how determined is heat to pass through the entirety of the chimney mass -- does it seek to equalize all mass materials via thermal bridging, before radiating into the house?