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reducing combustion-unit dimensions on 8" system?  RSS feed

 
Posts: 17
Location: Detroit, Michigan
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the standard height of the metal drum surrounding the heat riser tends to be quite high on an 8" RMH system. following the design dimensions laid out by E & E (as well as Ianto), puts the top of the drum at about shoulder height. which is not an ideal cooking height.... at least not for a 5'8" kind of dude...

if proportions for heat riser (3x), burn tunnel (1.5x), and feed tube (x) are still followed & as well all cross-sectional areas are kept unchanged... can i still expect good performance if the dimensions are dropped PROPORTIONALLY?
i am hoping to have a heat riser height of 41.5", a burn tunnel length of 20.75", & a feed tube length of 13.8. this would put the top of the barrel at elbow-height, rather than shoulder.

a couple additional pieces of info:
we are only running 44" linear run through the mass (so a little less pump-effect could be tolerated)
we are exhausting into a 35" existing chimney (which acts as a second pump)







 
pollinator
Posts: 4154
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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NOTICE :

THE THREAD BELOW WAS POSTED DUE TO A POSTING ERROR IN GREG C.s BUILDING PLANS AND IS NOT RELATED TO THE 'REVELED FACTS'




Greg C.I understand that you are still need an answer to very pertinent questions regarding protecting the Wooden Exposures of your installation site!

This will add height to your build and the Whole height must also be figured as distance from the top of the bricks covering the burn tunnel By the time
you add the barrel gap you are inching back up there! you may well have to plan on a built-in stepping stool !

The p[roblem with Curtailing the greater part of your Thermal mass is you are only capturing the prompt heat that comes off of the Barrel approximately
40% of the total and only a very small pert of the remaining 60% you total will be near 50% total with 1/2 the heat being vented to the outdoors !

As soon as you stop burning a fire in your RMH you will rapidly lose all radiant heat off of your barrel and have a totally inadequate amount of thermal
mass to Carry you through a Michigan winter !

You will lose most of the fuel stingy benefits of the RMH, and need to feed your RMH most of the night or expect to be cold!

In many respects you would be better off with a conventional Iron box stove that you can build a smoldering fire in overnight,suffer the lower temperatures
and have something that will quickly warm you in the morning !

In the final analysis, the choice is yours, have a long talk now with your significant other and plan to how to get through this winter and prepare to go on
from there ! For the Good of the Craft ! Big AL
 
greg crawford
Posts: 17
Location: Detroit, Michigan
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thanks for the reply al, but your advise is a bit confusing:


allen lumley wrote: The p[roblem with Curtailing the greater part of your Thermal mass is you are only capturing the prompt heat that comes off of the Barrel approximately 40% of the total and only a very small pert of the remaining 60% you total will be near 50% total with 1/2 the heat being vented to the outdoors !



Al, by 'curtailing the greater part of my thermal mass' are you saying that my run of 44 linear feet is not enough for an 8" system, or, are you saying that reducing the dimensions of the combustion unit (proposed reduction is 6/7th or 86% the standard size) will cause a failure in system heat capacity/efficiency?
*if the former, you think a run of 44 linear feet (a loss of 6' in a standard 50' system) can be considered 'the greater part'? i suppose i can add another 6' feet to the mass run; if so, duly noted, but my question pertains to the combustion unit.
*if the latter, what does the combustion unit dimensions have to do with curtailing the thermal mass? that the heat generation/output would be decreased by a proportional reduction in combustion unit dimensions?


allen lumley wrote: Whole height must also be figured as distance from the top of the bricks covering the burn tunnel



this distance is simply the height of the heat riser, minus the 7" depth of the burn tunnel. again, nothing relating to cross-sectional area has been changed.


again, thanks for the response. i am hoping that once this is sorted out... i will be on my way to winter heat!
 
greg crawford
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Location: Detroit, Michigan
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Mister Ianto says in the 2nd edition that: "The height [of the heat riser] in the specimen 8-inch system shown is 33 inches, but could be anywhere from 25 to 50 inches."

with a heat riser height of 41.5" i should be clear (according to Ianto). then, if all dimensions are kept proportionally intact... couldn't i expect (logically-hope for) success?
 
allen lumley
pollinator
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Greg C. : a Typo sliped into your building plans Thread regarding your proposed length of your Thermal mass !

The thought had popped into my head you were having problems convincing your other half to let you drag all
that mud into your house !glad it was a typo! For the craft ! Big AL
 
greg crawford
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Location: Detroit, Michigan
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allen lumley wrote:Greg C. : a Typo sliped into your building plans Thread regarding your proposed length of your Thermal mass !

The thought had popped into my head you were having problems convincing your other half to let you drag all
that mud into your house !glad it was a typo! For the craft ! Big AL



aha, yes, so i have decided to drag all that mud into my house! i will be building a double-bed-sized mass-platform, & abandoning the plunger-tube which would utilize the chimney's mass.

and so, what do you think about my question now
 
allen lumley
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Greg C. : Yes go for it !

I would highly recommend the whole build it out doors 1st, dry stack the fire bricks and take pictures with your phones camera, So that you can duplicate
the exact same to spec.s build every time, allowing you to concentrate on Level and plumb!

NO ONE has ever said to me that doing that was a waste of their time, Everyone praised these steps as allowing them to do a much better job than going
immediately with the Build ! Good luck, Take a few pictures to share ! for the Good of the Craft! Big AL

Late note : You may well be able to shorten the burn tunnel by a brick or two without any noticeable effect, otherwise consider that figure right at the
maximum length ! A.L.
 
greg crawford
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Location: Detroit, Michigan
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just want to clarify: you believe that the proportional reduction in dimensions should work?

yes, i will do a dry-stack outside, you've talked me into it! in fact, the whole project may as well even be faster, with what i learn in the dry test

thanks again al!
 
allen lumley
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Greg C. it looks like a proportionally correct build, whats not to like ! Again two sets of pictures at every step of the way ,

1) Good for I don't think It looked like this last time and 2) for the album of photos to show of the start of your 'Mad Skills '

The idea of the mortar is not to stick the bricks together but toehold them far enough apart to over come any surface
irregularities, allowing you to build Plumb, level, straight and true (and from that, Great L@@King).

The ideal sand will sound gritty when rubbed together with thumb and finger close to your ear, the mortar made Can Not be
spread finer than the biggest grain of sand in the mortar batch !

Always have your cleanest straightest sides facing into the combustion zone ! Big AL
 
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