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Post by fireboxfrankie on Jun 26, 2015 12:12:09 GMT -8
sorry to ask these questions again, but briefly
what is the recommended ISA for a seven inch system? is there a thread i should take a look at?
if i cast the riser, does it need to be split down the length for expansion or can i get away doing it in one?
what's the advantage of putting superwool between the two skins of a double skinned bell, as opposed to a 5mm air gap ?
have now built the wall that surrounds the stove, stove building starts in a week
many thanks
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Post by peterberg on Jul 1, 2015 11:24:36 GMT -8
Better have the cast riser split lengthwise. You could do with just one side a split and the rest as a whole, that should work too. Assuming the maximum ISA of a 6" system is 5.5 m2 or 59.2 sq in, a 7" system probably would be able to drive 7.48 m2. This is halfway between 5.5 and 9.7 m2, being 6" and 8" systems. Keep in mind, these are maximum figures.
Very sensible to have some adjustable ISA. The air gap has the disadvantage that there can fall some mortar in the gap and there you have contact between the innner and outer skin which you should avoid at all cost. It will inevitably lead to cracks in the outer skin.
I am very curiuous what your experiences will be. Please keep us posted, this will add more hard numbers to the reference library.
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Post by fireboxfrankie on Jul 3, 2015 11:48:02 GMT -8
hi peter thanks for the reply, yep will keep you all posted, quite excited to see what i discover, to start a couple of pics showing brick layout, outer skin , inner skin and firebox with exit into bench at back returning to chimney in front just to clarify when you say on side split, could a shim of metal be vertically placed from top to bottom within the cast, this could be gently removed or slowly be allowed to burn out allowing a tiny bit of expansion, am i thinking correctly? also could i built the two skins with cardboard betweenthem, this also would burn out giving an accurate mortar free gap and avoid another purchase thank you Attachments:
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Post by peterberg on Jul 3, 2015 12:07:00 GMT -8
What I see there is left and right of the firebox three skins. That isn't necessary when those skins are that close to each other. Maybe I misinterpret this but just to make sure you got it right. And yes, you could use a steel plate to be pulled out when the build is ready or have cardboard between those skins. Beware though, just tiny leak in the outer skin you room will be filled with smoke until the cardboard is completely charred.
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Post by fireboxfrankie on Jul 3, 2015 23:13:57 GMT -8
the inner skin is the firebox followed by two more skins, it didn't feel like a good idea to build the inner skin of bricks on top of the firebox as it will be quite high approx 1.80m, that was my thinking
ta again
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Post by satamax on Jul 4, 2015 0:41:10 GMT -8
a thing i have sugested before, and that Peter thought it was a good idea.
Put some steel wool between your inner and outer skin. The steel counteracting somewhat the insulative effect of the air pockets.
Tho, i don't know where to find big rolls of it.
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morticcio
Full Member
"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
Posts: 371
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Post by morticcio on Jul 4, 2015 1:43:52 GMT -8
Thanks for posting photos Francis. Are the two channels on the right for benches?
The planning officer here (aka my wife) likes the curve on the foundations at the front of the firebox.
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Post by fireboxfrankie on Jul 4, 2015 12:02:03 GMT -8
peter what size slit in mm would be optimum and its more than a couple of mm then does than compromise performance by not containing the fire , gases and heat?
thanks sata will look into into it, andy yep the two channels are for benches, is this going to be the one to convince the officer? more pictures this week...
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Post by fireboxfrankie on Jul 4, 2015 12:04:42 GMT -8
sorry meant to write
what size slit in mm would be optimum and if its more than a couple of mm then does that not compromise performance by not containing the fire, gases and heat?
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Post by peterberg on Jul 4, 2015 12:29:54 GMT -8
It doesn't need to be more than a couple of mm. The whole effect is this: heat is transferred by convection to the inner walls, coming through by conduction. Transferred by radiation to the outer wall, coming through by conduction again and than by radiation and convection leaving the outer wall. It doesn't compromise performance, the higher the temperature difference, called delta T, the quicker the heat comes through.
The whole process of changing by sort of transport a couple of times will slow down tranmission of heat greatly. In this way, it can be 24 hours or more before all the heat has left the mass. When you want even less speed, use insulation material between inner and outer wall. Even 50 mm of rockwool won't block the heat completely, only slow it down. In Finland there's 10 mm hard rockwool available which is ideal for this purpose. Haven't heard of another country where this is available.
hope this is clear
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Post by fireboxfrankie on Jul 4, 2015 13:28:51 GMT -8
my mistake peter, i understand the gaps and insulation between the inner and outer walls, i have used similar systems in the masonry stove i built, my question refers to the single vertical split in the riser, is a couple of mm enough or does it need to be more? what is the optimum, i thought to wrap the riser with dense 25mm superwool
thanks for you patience in answering all these questions
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Post by peterberg on Jul 4, 2015 23:01:58 GMT -8
Ahhh... I see what you mean, that's a completely different subject. The riser, when cast as a whole, will crack rather sooner than later because of uneven rise in temperature in the horizontal plane. Not the heated side will crack but one of the others due to expansion of the hotter side. When you look at it, with one vertical split the riser walls are able to expand freely.
And now the answer: the size of that split isn't important. Of course you need to stuff a crevice of several mm's with superwool but a split of paper thickness would be adequate as well. A thin metal plate would work for you and the 25 mm superwool around the riser would seal it adequately.
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Post by fireboxfrankie on Jul 5, 2015 0:02:16 GMT -8
fantastic, setting up the cast today, casting tommorow and start to build on wednesday morning with 4 others eager to help and find out about the petersberg batch box, if your ever anywhere near west wales please come and say hello, will keep progress posted
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Post by fireboxfrankie on Jul 16, 2015 23:54:15 GMT -8
the build so far, will send a link soon of the whole build and then a wee wait till we fire up, thank you all very for your assistance in helping to realise this one
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