Hi Andy. My shop is 113M², and i heat the flat above with the rocket too. I have 54m² approximately.
That's about 1200 and 600 sqft. Floors of the flat are wooden, and insulated with 14cm wood fibers.
Barely any insulation on the hollow brick walls, besides the strawbales i've piled up against these. 12cm of cork panels in the roof. Nowhere near enough for here. That's a workshop i bought from a pothead, with no concrete pad on the floor, nor doors. It's been a chore to work with the hollow bricks, since i got it.
I get cold inside, when it reaches -18, -20. I have then to redo a burn in the morning, and three loads of the firebox at night. With -20, in the morning around 8 o clock, it's down to 17c° It wouldn't go two days, then; without burning.
I have R6 US value, approximately in the brick walls. May be R7, at the flat's height, with the wood siding. And little insulation behind. R17 us, in the roof. No insulated concrete pad.
Thanks for the link. That is a big boy. How was the steaks? I like the idea of cooking on a stove.
It's hard to learn to cook on it. Controlling the temps, or even knowing the temps is complicated. But i get better at it. The oven was a lovely addition. The top of the firebox plate, is perfect for stews, and sizing steaks. Thought, that stinks the whole place.
The things i would do differently now, is less, metallic surface, for less fast heat. Because it overheats the place, and more mass. I think leaving just the firebox and oven door, plus the cooking plate is sufficient for my fast heat needs. Mind you, when it's real cold, it might not be. It's hard to find a happy medium.
You know the two "legs" of the angle being heated differently, one being in contact with the cement board, a sort of heatsink; and the other one fully in the hot gases. I thought that it could cause twisting.
Robbie Mendelssohn wrote:Thanks again to all who have helped out, I'm now constructing the bell...I have a technical question: I have scaled the core to a 175mm system as that is the available tube. But now my floor channel is 67mm wide. I can only get 70x30 or 60x30 tube, so should I go bigger, or smaller? or do I need to fabricate my own tube, which will be tricky....? Thanks guys!!!
60x3 good at lower altitudes, bellow 800m elevation. 70x30 above.
Chimney and through the roof, chimney, chimney and chimney. That is the only answer. Nothing else. Venting through walls, window is just asking for trouble, or death. If you could take pics of your interior, it would be helpful.
Robbie, with a black oven, i don't seem to reach more than 120 celcius at the bottom of the oven, at the first burn. 180/200 C° at the second burn, 300C° at the third. And my rocket is a 220mm batch. About 9 inches.
Go corbel and steel plate if you want. How thick are those steel plates? But on top of a bell, avoid anything which could crack and collapse. Like homemade clay bricks.
What i was trying to say, in France, and Italy, they used to do this, reversed T bar, and hollow bricks laid on top, to hold the concrete above. Not for big spans thought.
I was thinking you could do this with firebricks, and with another layer on top, even of tiles. The only thing is not to mortar the two layers. But rather put a bed of sand, because of the heat expansion.
In your first video, with the flames shooting out, i can see the firebox crammed with bits of wood. I can see the pulsating, which to me means you don't have enough primary air. I'm quite high above sea level; and i had to increase the primary air. And i can tell you, i know your problem!
The solution has been to cut proper firewood.
I use larch now that i have my combine splitter machine, which might give me trouble again; But with oak that big and even a bit smaller, it was fine.
If you use softwood offcuts to light the stove, don't fill more than a third of the firebox, half absolute maximum. When they are at half ember stage, add bigger wood. If you want to burn those to get rid of waste, mix these with bigger wood. In my firebox, which is 33cm wide iirc, x 50cm high. I put 6 to 8 pieces of wood, about 10cm shorter than the firebox itself. Always leave a space at either end for the air to spread, and for the flames to develop. Always leave space above the wood. Don't burn too much fatwood.
I admit, i have an advantage to monitor my fire, with the window above the heat riser.
Robbie Mendelssohn wrote:I say it would be a bit like a bell in that it has extra volume, being of larger diameter and the exhaust would still be moving slowly compared to when it narrows at the vertical chimney. I bought the tubes today so I hope I'm right...
I did read the post to the end as recommended and was thoroughly entertained, I like the science fair interlude.
Is that ytong block wrapping the firebox? I was considering using it until I dug deep and spend a staggering quantity on ceramic fibreboard.
Here's a question.... To make a slab for the top instead of steel, can I cast one like someone said here with clay and sand and arlite? I can't find a refractory slab around here.... And, why arlite? Isn't it insulating, rather than accumulating,,? Also, I'd hate to see it collapse and crush my fibreboard riser :-p
Yep it is ytong. I had to support it, because it cracked. But so far, the core is holding. The flue elements behind, for the riser, not so well thought.
Clay perlite sand for the bell's top? This is a joke? Even if expensive, buy the proper stuff. refractory of good quality. Or make a composite bell top. T bar steel. And firebricks, gas proofed by superwool and in a criss cross two layers.
Well, my opinion, having played with J tube a fair bit.
Batch boxes are better. Nowhere near as much tending, nor smokeback. Far more powerful. Plenty of design tricks to cook and heat. Even hot water and central heating possibilities for the one willing to invest in doing it right.
I would not mess with J tubes, anymore, besides outside cooking.
Peter van den Berg wrote:For conversion of imperial to metrics and vise versa I am using Cleave Books Specialist Calculators. About any conversion is in there, money excluded. Satamax is right, but you are gonna use imperial I'd think.
Having learned guitarmaking at school in uk, and in the book of Cumpiano and Nathelson. Where it's all in inches. I am used to do the conversions with a calculator. Pretty easy once you have the basic numbers in your head.
Imperial decimal, and imperial fractional! Why guys, why?
Gerry Parent wrote:This is all becoming a lot more clear. Thank you both.
Now, if I can reiterate what was said for clarity.
The port for a 6" batch box from Peters chart is 2.19" x 9.5" = 20.81 sq in (52.86 sq cm) Nope, 20.81 x 6.5416 = 134.257796 cm².
So 5% of 20.81 (52.86) = 1.04 sq in (2.64 sq cm) Nope again, 134.257796 X 1.05 = 140.97 cm²
Total hole or slot size on top of riser then needs to be: 20.81 + 2.64 = 23.45 sq cm
With this second port added to the riser, its now sounding a lot like Matt Walkers riserless core design which also has 2 ports with an expansion space inbetween them (just laid down level)
Think I might try a circle first made with cf blanket.
Cf board would be a better choice but I don't have any on hand.
Also, with the wrinkled nature of the cf blanket at the top of the riser, doesn't make it a real accurate science but I guess close enough will have to do.
Peter: Glad to hear the experiment is repeatable and predictable and to know that more height is not always better.
I'm having a bit of trouble visualising your "end port" idea. You said the lid has a hole that is 5-10% larger than the riser port. Did you really mean smaller? I'm not sure how it would help to restrict the flow if made larger.
I would assume that this lid could be made out of the same 1" cf blanket with the circle cut made on an angle to act like a funnel?
Seems like a simple enough experiment to try before removing the extra length of riser. Might need to observe it from outside though if it decides to smoke violently again!
Nope, Peter is speaking of the "port" at the end of the firebox. And he is talking about 5>10% larger than it's surface area.
Your port is 128.52 cm² surface area. Or approximately.
So 5% bigger
128.52 x 1.05 = 134.946 135 cm²
128.52 x 1.1 = 141.372 141.37 cm²
Let say you go for 5%
135 x 4 = 540
540 / PI =171.887
Square root of 171.887 = 13.11cm diameter for the hole in the heat riser doughnut.
I don't know what temp to control. And where to control it.
Well, i would like to know the bottom stone temp, to check if pizza making is possible. But do i drill the stone and put the probe inside ? Do i lay the probe right on the stone at the back? Or do i measure the temp of the oven halfway up? The two later solutions mean that i would have to put the probe at the back against the bricks which are now on the back of the oven.
Another trick to attach metal parts to bricks, a glass fiber, or fireproof joint behind the lip. And holding it to the backside of the
bricks with restraint strap you know, the coiled, pierced metallic straps? Held with the smallest type of rawlplug you can find.