RMH - How narrow is too narrow?

Gerry Parent wrote:Hi Errol,    Another option: If you can get your hands on an old/dead electric hot water heater, they have a metal core in them that can serve as a 'barrel'. Here in Canada, they are
18" - 20" in diameter (depending on the size of hot water tank). This is what I have been using in my shop for quite a while and works quite well. If you have a cut-off wheel on your grinder, your good to go. All it requires to purchase is black pipe caps to plug up the bung holes.

errol hall wrote:Yea,  good idea.  Unfortunately all the scrap metal get hoovered up by so many little outfits going round with vans picking it all up to make a living.  It's gettin' kinda mad max up in here!

Gerry Parent wrote:

errol hall wrote:Yea,  good idea.  Unfortunately all the scrap metal get hoovered up by so many little outfits going round with vans picking it all up to make a living.  It's gettin' kinda mad max up in here!

Those tanks mounted on the center truck/car.. thing would be perfect!  Now, just gotta get past those freaks and your downtown!

Glenn Herbert wrote:2" of perlite-clay for riser insulation is standard, but in your situation I think it would work well enough to reduce it to 1" or 1 1/4", giving you the outer gap you need for downflow.

I would advise against trying a system smaller than 6" for your first build; that is the smallest size that tends to be reliable, and you want it to just work without adjustment and tweaking.

Can you get your hands on any sort of clay, and stones or brick pieces? If so, I would use that as the base for the manifold and set your "barrel" into it. This would let you make the transition space plenty large. How tall are the tanks you have, excluding domed top & bottom? You will want at least three feet from base of burn tunnel for riser clearance. I would make the duct transition almost as big in diameter as the (little) tanks for safety in flow.

And keep your eyes open for materials you can grab (legally ) as you enjoy the warmth from this first setup, to make up a bigger, better one for next winter.

Ralph Kettell wrote:Hi Glenn and Errol,

I had the thought to reduce the insulation thickness also before I got down to your post.  Running the math seems to indicate that reducing the insulation to 1.5" would be sufficient.  The CSA  of a 6" system is 28.3 si.  With 1.5" of insulation the I.D. of the outer gap is 9" and the O.D. is 12.4".  This gives a CSA of (12.4^2-9^2)*pi/4 = 57.1 si which is just over twice the CSA.  The gap is only 1.7", but if the surfaces are fairly smooth it should function just fine.  You might want to buy Erica and Ernies book just to read their design rules of thumb and their construction hints.[/quote

Wow!  Thanks so much Ralph, truly impressed by your mathematicizing on this (yes I know that not a word - I just like making them up!).  Really appreciate your help on this inc the tip on the smooth sides.  I'll take a look at that book.

It's a sunny late autumn / winter's day in old Blighty right now; all pre-Crimbo.  A time for the first Robins of Christmas...and metal cutting.  

Wishing you all the peace and good will of the season.  

Hail Permies, We are well-met.

Gerry Parent wrote:

errol hall wrote:Yea,  good idea.  Unfortunately all the scrap metal get hoovered up by so many little outfits going round with vans picking it all up to make a living.  It's gettin' kinda mad max up in here!

Those tanks mounted on the center truck/car.. thing would be perfect!  Now, just gotta get past those freaks and your downtown!

Glenn Herbert wrote:If you're not experienced in making molds for casting things, I think you would find it considerably easier to build with firebrick, and wrap insulation around it.

Trying to interpret your core dimensions, it looks like a 12" high feed tube, or maybe about 16" counting the thickness above it? Then 18" total floor length of burn tunnel, which is good for a 6" system, and about 34" total height of riser (from the burn tunnel floor), which is just about enough to fit with the other fundamental dimensions. If you are planning on a total feed depth of 16", the riser may not be tall enough; I would add a couple of courses of firebrick on edge to raise the barrel and the riser, in that case.

errol hall wrote:

Glenn Herbert wrote:If you're not experienced in making molds for casting things, I think you would find it considerably easier to build with firebrick, and wrap insulation around it.

Trying to interpret your core dimensions, it looks like a 12" high feed tube, or maybe about 16" counting the thickness above it? Then 18" total floor length of burn tunnel, which is good for a 6" system, and about 34" total height of riser (from the burn tunnel floor), which is just about enough to fit with the other fundamental dimensions. If you are planning on a total feed depth of 16", the riser may not be tall enough; I would add a couple of courses of firebrick on edge to raise the barrel and the riser, in that case.

Cheers Glen.  The drawing is a little misleading.  The design dimension are actually Feed tube 12"; Burn Tube 18"; Heat Riser 36". Because I have limited bell height I need to accommodate more of the heat riser length in the lower half of the design.  This requires lowering the front of the feed tunnel to maintain the 12" height - please see new pic.  Do you think this approach would work?  Ther will be some kind of cover to seal the front clean-out hole.

Btw I have realised there is a mistake in the drawing dimensions.  I will correct and re-post.  

Must say I really value your sustained interest and input on this.  As we say in Ole' Blighty 'Your a diamond mate'.

Roak Wolf wrote: My stove Roars great with barely 2 inch between the barrel and riser. my riser is made of dense heavy fire bricks along with the rest of my stove. Has a gap of 2 inch between top of riser and top of barrel. My burn tunnel is 4.5 inch wide 6.75 inch tall and i am running a small brick mass/bell after the barrel and 8 inch chimney. When burning pellets i get an awesome Blue/purple flame!

errol hall wrote:

Roak Wolf wrote: My stove Roars great with barely 2 inch between the barrel and riser. my riser is made of dense heavy fire bricks along with the rest of my stove. Has a gap of 2 inch between top of riser and top of barrel. My burn tunnel is 4.5 inch wide 6.75 inch tall and i am running a small brick mass/bell after the barrel and 8 inch chimney. When burning pellets i get an awesome Blue/purple flame!

Sure would like to hear (and feel) that baby roar!  Flame colour is gorgeous - any particular type of wood pellet?  Lots of MASS!

:-)

Ez