Breaking News! Shop Dragon admitted to I.C.U. !!

thomas rubino wrote:By using a piece of angle , held in place by the last two angled bricks. This would deflect possible sparks but not impede the airflow!
Is this correct ?

Yes, it is. It also helps against pieces of coal that could roll down in front of the air inlet. And as I said, to keep the ashes in. What you are experience now is the original setup what it was like with an overhead p-channel. Air is blown straight into the fire and by doing that fuel overload point is reached earlier. The floor channel and threshold combination slows startup down somewhat but fuel overload chance is deminished. And last but not least: in Matt's layout the primary air is higher up as well.

thomas rubino wrote:I am wondering if my primary air hole is large enough? I went with 5" wide by 1.25 tall = 6.25 " The secondary air is 1.75 x 3.5 = 6.12"
I am getting a complete burn with very little ash left at the end, so maybe those are the correct sizes?  I believe I followed your parameters.
It just feels like it would burn even better with a larger primary air. Or would adding extra primary air change the burn to be less than optimal?

The primary air is large enough, on average it's about 25% of a round riser, in your case 4.9" sq. That said, in my own 6" system the combined air inlet is 24.5% at most. My heater is presumably running with lower air excess and efficiency should be higher as a consequence. Yours will run fine as it is, given the low exhaust temperatures. Keep the thing running day by day until it's getting too warm outside, sensible conclusions about this setup can be drawn when running in period is done.

Thank You very much Peter!
I sure appreciate all the great advice you have given me and any one else who needs guidance!
Your monitoring of posts here and over at Donkeys.
Your timely responses  to them, have helped hundreds down the  path to clean efficient wood burning!  

thomas rubino wrote:Hi All ;
Took the dragon out for a long flight this morning!  Five loads of fuel later... We were cruising!
My shop was warmer than it has ever been! Admittedly it was in the 40's outside.
Barrel temps of 320 on the lower and 465 on the upper.
Brick bell temps were 120  near the barrel and 90's down at the floor. Those numbers would have continued to rise had I kept burning.
Exhaust stack, gas temperature , checked with a T & G dragon breath monitor, reached 145 F at the end of the last load.That is significantly lower than I was getting before with a single barrel.
That temperature would also have continued to rise.
After  the last load went out. I fabricated a ceramic board plug to seal my primary air off when not burning. The secondary air just got a piece of cf board propped in front.
Both will help keep all that generated heat right there in my mass and not being sucked up the chimney.

Hi everybody.

Thomas, sorry to say, but i find your temps a smidge low. 145 F, that's really really low. That's the kind of temp i get after five minute burn, on a warm stove. Ok, mine is a 9 incher or so.

End of the load, i am at 240 F / 250 F, mid stream of the 8"x 8" chimney.

This is with 1.9 m² of radiating metal, and about 11 m² approximately of mass ISA (or is it total ISA? can't remember)

Usual temp for me just above the riser, 8" above and may be 8" off to the side is 370 C°,  5 cm inside the barrel.   So that's 700 F more or less at 6' above the workshop floor.

I think i could extract a bit more. But i don't think i will ever go down to 145 F too close to stalling temp imho. I already get smoke filled workshop every now and then,  with what i have. Usually in the spring or summer, on a cold and rainy day, when  the outside temp is rather close to inside temp, atmospheric pressure is low. and a stone cold stove.

My feeling, is that you have too much primary heat extraction with those two barrels.

HTH.

Thank You Max;
I have considered that could be the case.
If need be I can insulate a part of or all of a barrel.
This stove needs to dry out and warm up first, before I judge it as to cool.
Besides , even now with very marginal temp differences outdoors  and a not dry core , I have no smoke back.
Maximum extraction sounds like a good thing in this case, the shop might only get used 4-5 hours a day in the winter.
With a 16' ceiling no insulation and 10' shop doors that open. I need every btu I can get.
This same bell with an 8" J tube and 1 barrel ran flue gas temps of 250 + After it was warmed up.
I would hope a 7" batch can support one extra barrel over a J tube?

A 9" stove eh! Wow that's a big one.  Peter suggested to me that an 8" might be to large.

thomas rubino wrote:
This same bell with an 8" J tube and 1 barrel ran flue gas temps of 250 + After it was warmed up.
I would hope a 7" batch can support one extra barrel over a J tube?

A 9" stove eh! Wow that's a big one.  Peter suggested to me that an 8" might be to large.

Thomas, The nine incher is my workshop thing. I heat 635 cubic meters approximately with it. Barely no insulation in the roof, 12cm of cork panels. Which is an euro R of 3, R17 in the us.  Hollow brick walls, R1 theoretically that's us R6, and loose strawbales leaned on the walls, that if these were stuck and plastered would give a US R of 34. But this is bare straw, for the moment.
If your 8 J was doing 250, the 7 incher batch should do the same at least. I have a fair bit more primary air than recommended, due to the altitude, 5000ft elevation.

Your seven incher should be able to cope with that extra barrel. I think, with a well running 7", you should be able to cope with a 8 m² or 9 m² total ISA. ( barrel and mass)

There is one thing i have noticed. I find your secondary port a smidge close to the port.

Peter van den Berg wrote:The primary air is large enough, on average it's about 25% of a round riser, in your case 4.9" sq. That said, in my own 6" system the combined air inlet is 24.5% at most. My heater is presumably running with lower air excess and efficiency should be higher as a consequence. Yours will run fine as it is, given the low exhaust temperatures. Keep the thing running day by day until it's getting too warm outside, sensible conclusions about this setup can be drawn when running in period is done.

Spotted a mistake, yours is a 7", not a 5", my bad. So a combined air intake like mine for a 7" should be on average 9.6" sq. It might be that your primary inlet could be somewhat larger, hard to say since the inlets are separated. When the heater is all dry, using a larger inlet means chimney temp will be higher. As I mentioned, I start the thing with the door open a crack. When I forget to close it further down the burn the chimney temp tend to rise up to 120 ºC or more. Ermmm... that's equivalent to 248 ºF, I regard this as higher than necessary. The 140 ºF you mention is quite low, just above condensation temperature. But then, as long there's no puddle of condensation fluid to be seen anywhere at the base of your heater you're good.

Update;  Today,s weather report, cloudy , cool and threatening rain. Temps in mid to upper 40's.
3 loads of wood  thru the stove.  
Flue temp now over 153 F !
Room temp today becoming too hot! Those double barrels really throw the heat out!
Still steam but only for a few feet before dissipating.

hey man, kinda new to all of this and in my research phase still, was wandering, I didn't see a riser core in the pictures before you put the double barrels on, Is there a riser in there or is that something that's not necessary in this particular design? thanks for posting up all the great pics and info!

There sure is David;  A ceramic blanket (5 minute) riser.  
Look closer at page one. You will see the old 8" 5 minute riser I removed and the shorter 7" riser I installed.
The 8" riser will move over to our other RMH in the wife's artist studio.

A 5 minute riser looks just like a piece of regular single wall stove pipe... because that is what it is!
The Ceramic Blanket inside protects the pipe from the intense heat generated in a RMH.

nice! thanks! looks super easy to make