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Draw too strong?  RSS feed

 
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Simply asking if the draw can be too great while burning. Even when at 40 degrees and hasn't been burned in all week the draw is incredibly strong.  Don't get me wrong during the summer it will be great, but am I losing heating time and could it be cooling the system or incomplete burns. I ask because the top of my barrel is barely getting to 400 degrees during an intense burn and just burning its about 280 degrees normally but even with the door wide open or almost closed the draft is VERY strong. I did finally order the book off Amazon will be here Friday, any suggestions
 
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Location: latitude 47 N.W. montana zone 6A
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Hi Anthony;  Welcome to permies!  We need more information to help you out.  Pictures would help also.  Something is off .. 280- 400 F at the barrel top is low. Nobody I have heard of has ever complained about too much draw!  Why would you need a summer time  fire in a mass heater anyway ??? How much horizontal pipe are you running ?  Is it buried in a mass yet ? Dimensions you built with ?  Lots of questions need answers . J tube RMH are simple but ... they need specific dimensions at the core & the mass to work properly. Give us more information... read the book ... take pictures...  ( EDIT) How is it you have a door on a rmh ???  they don't have a door??? 
 
Anthony Carlson
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TY Thomas,

the summer, I was told it will also cool the cob in the summer with enough draw

I'm running 15ish Feet straight 5" black stove pipe then 11ish Feet straight out the roof doubled wall stove pipe, I did not double through the cob

It is in cob imgur link https://imgur.com/a/762If

The Jtube is 5x5 square stock (yes it's metal and before I found permies) with a 12" feed tube x 24" burn chamber x 36" riser in cased in a 10" (I think) pipe with perlite and fire clay insulated, I do have pics of it but not in that imgur link

There are 2 doors wielded on the top and a clean out on the front

But yes the top of the barrel is getting just over 400 and only if I'm feeding it as much as it can burn as quickly as possible. If not and just feeding it every 15 to 20 mins then between 280 and 320.
I did use a laser heat gun to check and it was with 3 to 9 degrees of the one at work so I think its fairly accurate and the one in the pics seemed to be under but fairly close to each other also
 
thomas rubino
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Location: latitude 47 N.W. montana zone 6A
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Anthony; I'll TRY not to harp about the metal core...  What I do see, your build looks really nice , other than the...XXX core...   What is the top gap on your riser? Too large a gap and you won't get the high temps at the barrel top  Your transition area has to be large enough already, if your getting that a good draw.  What is the mass temp? What is the stack temp after leaving the mass? Are you getting only steam or heat shimmers out of the chimney top ?  Although 5" is smaller than recommended and the XXX core  is limited in life .Your rmh may.. be working fine and just need a little tweaking like decreasing the top gap . This next spring / summer after your much more knowledgeable from reading the builders guide...  I would consider maybe doing a core rebuild using a more insulating material than your current one.  Carbon fiber boards come to mind...  Read the book , read the info here at permies.  Don't talk about the XXX core till your replacing it ... LOL.   Oh , yes the bench sort of works as a cool spot in the summer if it remains totally shaded .... but don't expect too much.
 
Anthony Carlson
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1 1/2 inches is my top gap

Cold my mass temp is 30s after burning all weekend the parts close to the barrel are 120-140s but by the flue is 50-60s and still very wet and steamy,  all over steamy but mostly by the flue

No, I'm getting actual smoke out my flue with wood smells and all. I haven't taken temps at the top of the stack, I live on a hill and it's snowed and there's ice on the roof and of course the garage it at the edge of the hill
The flue inside (double walled) is getting around 70

And yes after reading the book a core rebuild may be necessary
I used all fire clay and sand cob in the build (1 clay to 3 sand) with concrete walls and stone in between them with the cob on top
Thank you again
 
thomas rubino
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Sounds like your cob is still drying out, this can take a month or two depending on conditions.  As your cob dries you will get better temperatures .... however I have doubts your design will ever reach true RMH burn temps.  When a RMH is dry and up to full roar your barrel top should have a glowing orange circle over the riser, temp there should be 1000-1100 F although some run in the 600-800 F range ,depends on top gap and overall design . At those temps you are getting a complete burn apx 95% efficient.  No smoke other than steam should be coming out the stack. Exhaust temps on the pipe should be in the 130 F range.  Very little ash is left after those temps.  On your current system you may have to check for excessive ash buildup in your horizontal run before spring comes... hopefully you built  in a horizontal clean out ?  Here are a few tips for you, if you decide to rebuild. Fire clay is really only needed at the core... plain old clay & sand will work everywhere else. Black stove pipe is only needed as the first pipe leaving your transition area, then you can switch to cheap HVAC pipe available in 5' lengths .I use one more piece of black pipe where I pop up out of my mass (its tougher than hvac pipe) then back to hvac pipe to the roof. Insulated (double wall) is really only needed when exposed to cold air. Also in your mass, use as much large rock as you can , only use enough cob to fill air gaps and to make a final shell (if your using an exposed cob bench) Rock and brick hold heat better and longer than cob. I rebuild my first core 3 times over two years before I was happy with the results. I even did a core rebuild in the middle of winter one year when I found my horizontal pipes 1/2 full of ash...  My current system is an 8" J tube RMH  7.5 x 7.5 x 16" deep feed tube. Burn tunnel is 7.5 wide by 8.5 tall  with a 12" roof and my fireclay/perlite  home made riser is 51" tall , 14' of horizontal run then a 180 turn and 11' back towards the core and one more 90 degree turn up and my vertical pipe goes to the roof . It roars ! The plastic green house /studio my RMH is in, used to use 12-15 cord of wood to stay above freezing all night (had to keep fire going all night as well) Now with the RMH we use less than 5 cords ... have no fire all night long and it will be in the 40's out there on a single digit morning . This morning its 18 F / snowing and it is currently 50 degrees out there, we let the stove go out around 9 last night. At the end of winter I do an ash cleanout ... less than 1/2 a 5 gal pail !  Try that with a box stove...
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studio RMH
 
Not so fast naughty spawn! I want you to know about
Two part roundwood timber framing workshop sep 24-29 and oct 1-5
https://permies.com/t/91267/permaculture-projects/part-roundwood-timber-framing-workshop
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