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Clean-out & pipe angles, bench composition, straw near pipe, riser insulation, feed tube size

Posts: 28
Location: Lexington, KY
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I'm building an outdoor RMH bench 8" system (overview). Lots of questions/feedback desired on these topics if anyone's willing!

Clean-out angle:
Do I want to angle this down slightly toward the ground from the pipe level to afford any condensation an opportunity to run out of the pipes? I thought about having so many clean-outs for this reason and also to keep the pipes clean.
For that matter do I want to the whole system to angle slightly downward toward the creasote trap at the end?

Pipe angles:
As you can see my goal is for benches around an open fire pit so the angles for a hexagon will be 135*. I'm planning on sculpting these angles, with the straight lengths of steel pipe running up to the angle and then rounding out a turn with brick/clay. Perhaps I would get less drag though by just using a stove pipe 45* elbow like this?

Bench Composition:
I'd love a fast (30-45 mins?) time to heat up the bench for our bums/calves in the winter/spring. Hence the offset pipe/limestone toward one side. Is there a model to look to for this specific requirement (outdoor, quick heat-up, but not burn the bum)? Ianto's 2"/hr for stone is appealing but still slow. How much stone can I get away with to transfer heat faster and do I need to increase sand content to hold it all together better? Here's a sketch...

Or what about a sand 'pipe' or trough just above the pipe for super-fast conduction to a limestone-rich 2-3" cob topper?

Straw in cob near pipe:
Also, I accidentally used some cob that had straw in it around the chamber/manifold at the base/exit from the riser. Remove it? What's the risk of having straw there?

Riser insulation:
I'm finishing up the riser insulation per Ianto's book. This perlite/clay mix is making me nervous... is this stuff really going to hold together once the hardware cloth burns away? I used about 1:1 by volume clay (pudding texture after wet sifting of all rocks) and it ends up pretty sticky and compacted once mixed and tamped in. Is this what it's supposed to look like?

Also, do I need to put a thin coating of well-sifted wet clay on the hardware cloth after scraping off the excess that pops out?

Feed tube size:
Is it necessary to add the additional 14" barrel (section of water heater)? If so why? And the book says 12", but does that make sense for my specs? Seems it would skew my ratio. Also if I do add the 12" of barrel over the brick part of the feed tube then does it need a top to make the mouth smaller and if so, is smaller better? Same 7x7" appx dimension?

Posts: 3113
Location: Upstate NY, zone 5
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The feed tube extension barrel is optional; most builds I have seen in photos do not include it. If you do use one, it should probably stay large so as not to act as a taller feed tube and decrease the draft from the heat riser to feed tube differential height.
Remy Olson
Posts: 28
Location: Lexington, KY
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Thank you, Glenn. I will experiment without it first then. I cut 12" of electric water heater length if I end up needing it. Would love input on the other Q's. Are they 'bad' questions? Too many? Wrong forum format? Or is it slow due to the holidays? Newbie forum user here...
Remy Olson
Posts: 28
Location: Lexington, KY
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Finished the riser insulation and put a cap of sand/clay and then pure smooth clay and will trip the hardware cloth once the barrel is fitted/placed. We also put a layer of pure well-filtered clay on the riser and it's smooth-er than the hardware cloth but still not as smooth as I'd like. https://www.flickr.com/photos/remyolson/16205296781/in/set-72157648483903247

Would love feedback on the bench composition and clean-out angles.
Posts: 4154
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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Remy Olson : Yes, it was a lot of questions, also Permies.comwas Self reporting Conectile Difficulties It was a little daunting to think of losing all that

So lets try now! The first 3rd can run up hill, as the gases are still hot, then any downhill slope is sufficient, a couple of clean outs should be sufficient, as long
as the type of elbows you use are NOT made by crimping the pipe to make that angle, price is everything!

A fellow member refers to the construction of the thermal mass as layers of lasagna, working All of one layer, set a Dense heavy Stone piece in place, then
dip it in Clay slip and set it into place using a minimum of cob to fill ALL voids, Layer by Layer, the more heavy dense stone you use the less Cob you have
to make and your Heat energy will be absorbed and transferred fastest.

Because every RMHs Thermal Mass is hand crafted, the rate your mass heats up and how it holds heat will vary a lot . Universally air gaps are poor planning,
think Monolithic mass

More and more every day we are moving towards adding more and more insulation, your cob with straw in it is insulative, don't work about it.

The hardware cloth should last a long time, E & E Wisner have been using it for at least 5 years now !

Make it as smooth you can, but keep it flush, a thin coating over the top will just flake off !

I am not a fan of any metal at the feed tube opening, also it is important to NEVER cap off the top of the feed tube while there is fuel in the combustion zone.

There, The best answers I can give, For the Good of the Crafts Big AL

Oh. Hi guys! Look at this tiny ad:
Rocket Mass Heater Plans: Annex 6
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