Post by madhatter on Jan 22, 2018 13:32:53 GMT -8
Hello everybody. I am from Germany and have already built two J-Tube mass heaters. Now I am planing a very small heater for my caravan 
. It should have a door so absolutely no sparks can jump out, a small cooking surface, air sould be drawn from the outside. No Mass besides the inner ceramics.
So the double shoebox in a tiny 3" configuration came to my mind. I set up a mockup to test it. The basic measurements were taken from Peter´s 3" BB dimensions. The first idea for the tunnel was to use the measurements of the heatriser for the 3" standard BB to keep it as compact as possible. That seemed to be so small and due to the vertical position it would be even shorter. So i made it 90x90mm square. It ran well, but the secondary burn still seemed to need more space, because the flames tend to shoot into the heat exchange box. I enlarged it to full width of the firebox und 3/4 of its hight (108x120mm). The volume now is a bit more than the standard heatriser. It performed well. My firebox is a bit longer than a standard 3" BB, because at the beginning I accidentally took the depth of the 4" Box (288mm instead of 210mm) but that extra space turned out to be usefull to put in 25cm pieces of wood. I didn´t see any negative with this depth so i didn´t change it.
At first fires there occured some signs of overfueling and hills of glowing charcoal in the back of the box. This was solved by a V shaped floor whith some holes in it to let some of the primary air go through the coals. That was a huge improvement and at the end there is no unburned charcoal left.
The exhaust looks and smells good. Actually it doesn´t look somehow because you can´t see anything, only a little smoke at cold start and when it is refueld. At the moment, when flames reach the port the smoke disappears.
The final heater will have a metal case with refractory plates in it. It would be possible to use vermiculite plates, but i will cast them on my own with an insulative mix.
. It should have a door so absolutely no sparks can jump out, a small cooking surface, air sould be drawn from the outside. No Mass besides the inner ceramics. So the double shoebox in a tiny 3" configuration came to my mind. I set up a mockup to test it. The basic measurements were taken from Peter´s 3" BB dimensions. The first idea for the tunnel was to use the measurements of the heatriser for the 3" standard BB to keep it as compact as possible. That seemed to be so small and due to the vertical position it would be even shorter. So i made it 90x90mm square. It ran well, but the secondary burn still seemed to need more space, because the flames tend to shoot into the heat exchange box. I enlarged it to full width of the firebox und 3/4 of its hight (108x120mm). The volume now is a bit more than the standard heatriser. It performed well. My firebox is a bit longer than a standard 3" BB, because at the beginning I accidentally took the depth of the 4" Box (288mm instead of 210mm) but that extra space turned out to be usefull to put in 25cm pieces of wood. I didn´t see any negative with this depth so i didn´t change it.
At first fires there occured some signs of overfueling and hills of glowing charcoal in the back of the box. This was solved by a V shaped floor whith some holes in it to let some of the primary air go through the coals. That was a huge improvement and at the end there is no unburned charcoal left.
The exhaust looks and smells good. Actually it doesn´t look somehow because you can´t see anything, only a little smoke at cold start and when it is refueld. At the moment, when flames reach the port the smoke disappears.
The final heater will have a metal case with refractory plates in it. It would be possible to use vermiculite plates, but i will cast them on my own with an insulative mix.
I would need air conditoning instead 
