Turning the combustion chamber around?

OK, so pretty much every build I've seen, including the little rmh currently in my house, have the feed out toward the living space and the bell positioned behind it, typically closer to the wall.  I'm trying to cram a new RMH into a rather tight space, and it would solve a lot of problems if I turn it around, so the feed is closer to the wall and the bell is out in the living space, away from the wall.  Given the space I'm working with, I think it will be much easier to protect the wall from occasional sparks than from the heat of the bell. I would still have enough room to access the feed tube to clean and feed wood (mostly from the side.) This orientation also would make that first clean out where the duct leaves the bell much easier to access, and makes it easier to keep the fur people away from the open flame.

Since I haven't seen this set up before - is there some important downside that I'm missing?  

Rough drawing (not quite to scale) of my plan.

I see no particular reason why you couldn't have the bell/barrel on the outside, as long as there is sufficient buffering of some sort to keep people from bumping into the hot surface. The feed near the wall is another matter; you will have significant heat there, both radiant from the top of the feed and conduction through the feed walls and surrounding mass. That would require serious insulation, plus a real air gap to any combustible walls, even with a metal heat shield and airspace on the wall.

If you pulled the feed out just enough to make the cleanout near it extend horizontally between the feed and the wall, that would make a separation that I would feel comfortable with.

I also notice the "outside door" which swings back close to the feed. You would have to make sure that door was noncombustible or shielded adequately.

The shape and size of your proposed bench leads me to recommend swapping the serpentine duct for a pair of half-barrel bells. Essentially, you cut a 55 gallon barrel in half lengthwise and put the cut edges down, with the duct from the manifold flowing into the bottom of the first barrel, out the bottom of the first into the bottom of the second, and out the bottom of the second to the chimney. This allows hot gases to rise to the top of each barrel and give up their heat, while the cooler gases drop and exit at the bottom. It would simplify construction and maintenance (fewer cleanouts to handle), and is reputed to be more efficient than just ducting. It would definitely reduce friction in the airflow.

http://s65.photobucket.com/user/mremine/library/NYC%20Rocket%20Stove%20Build/#/user/mremine/library/NYC%20Rocket%20Stove%20Build/?page=1&_suid=1472511087968034593128232003633

http://donkey32.proboards.com/thread/560

Kelly, what's the length and depth of the RMH's proposed footprint? RMH system size? Maybe a 6" system?

Glenn Herbert wrote:I see no particular reason why you couldn't have the bell/barrel on the outside, as long as there is sufficient buffering of some sort to keep people from bumping into the hot surface. The feed near the wall is another matter; you will have significant heat there, both radiant from the top of the feed and conduction through the feed walls and surrounding mass. That would require serious insulation, plus a real air gap to any combustible walls, even with a metal heat shield and airspace on the wall.

If you pulled the feed out just enough to make the cleanout near it extend horizontally between the feed and the wall, that would make a separation that I would feel comfortable with.

I also notice the "outside door" which swings back close to the feed. You would have to make sure that door was noncombustible or shielded adequately.

Right now it's just me and my good old dog in the house - I'm pretty good at not touching hot things. But I am dreaming up decorative shielding that will repel hands but let the heat out.  Will post picks if/when I get it done.

My experience so far has been that shielding the wall from the feed would be easier than shielding it from the bell - less area that will be subject to heat.  Right now it's looking like I'll have a 12 inch air gap between wall and feed, can't pull the combustion chamber out any farther from the wall or it will cover the crawl space access in the floor, though I might be able to squeeze another inch or two out of it.  I think I'll be able to insulate sufficiently in that space. The door is manageable I think - if it's cold enough to be burning, it's cold enough to close the danged door.    And it has an automatic closer on it, so it won't accidentally get left open.  And it's noncombustible.  

Glenn Herbert wrote:The shape and size of your proposed bench leads me to recommend swapping the serpentine duct for a pair of half-barrel bells. Essentially, you cut a 55 gallon barrel in half lengthwise and put the cut edges down, with the duct from the manifold flowing into the bottom of the first barrel, out the bottom of the first into the bottom of the second, and out the bottom of the second to the chimney. This allows hot gases to rise to the top of each barrel and give up their heat, while the cooler gases drop and exit at the bottom. It would simplify construction and maintenance (fewer cleanouts to handle), and is reputed to be more efficient than just ducting. It would definitely reduce friction in the airflow.

My drawing isn't quite to scale and doesn't really show the duct accurately.  I did consider half barrels instead of duct, and got to help a bit with one of Matt Walker's builds at a workshop, so I've seen how that works. But…decided duct might work better for what I'm doing.  This is a 6" system, but it will be 10" duct as it leaves the manifold, then the first two lengths of duct and the first 3 corners will actually be 8". It will go down to 6" for the third length of duct which will actually be on top of the second length, and inside the backrest of the bench. (I didn't draw the side view to show it accurately.)

So there will be 5 corners total (not ideal, I know) with 3 @ 8" diameter and 2 @ 6".  Hoping this will work and draw ok, and that the 8" corners will reduce drag just a little. I will have about 12' of vertical chimney, all but the last 2 feet indoors and warm.  And i can still make the heat riser a bit taller if needed.  The whole system is outside right now waiting for a fire ban to be lifted so I can test it. (We have crazy wildfires going on right now. Don't be the marshmallow!!!)

To answer Byron, the footprint will be 4'2" by 7'.

Satamax Antone wrote:http://s65.photobucket.com/user/mremine/library/NYC%20Rocket%20Stove%20Build/#/user/mremine/library/NYC%20Rocket%20Stove%20Build/?page=1&_suid=1472511087968034593128232003633

http://donkey32.proboards.com/thread/560

Satamax, that thread on Donkey's forum is a fun read. Thanks!  Haven't spent much time poking around over there….