To the size of the bell: I purposely undersized the bell. I don't recall seeing an ISA number for a bell/barrel combination. My concern was that the barrel would toss out a lot of heat, very quickly. It seemed reasonable that a fully sized bell, downstream from that barrel, would not leave enough heat in the exhaust to properly run the chimney.
You are right, until now there isn't a reliable ISA number for this barrel/bell combination. So you are now busy with the trustworthy task of finding out those numbers in relation to that core. The chimney diameter, length and quantity of insulation are other factors into play. Just to make it sound complicated, obviously.
Last Edit: Aug 1, 2013 8:05:08 GMT -8 by peterberg
If you decide you want more radiating capacity later, its easy enough to add a 2nd barrel on top of the 1st, and for that matter, it looks like it would be very easy to add bell space with your design.
Well.. I had a little fire in it today while taking coffee.. It's a warm day (not hot but warm) and a little windy. This time I was burning Redwood and Fir construction scrap that I saw up small (about 6 inches long and 1/2 inch wide) to make charcoal for the forge. It was a little more difficult to get it started, it smoked back at first. I tossed a piece of burning newspaper down the VERY short chimney (around 7 feet from the floor) and it was off and running.
It took about 10 minuets for ALL of the smoke to clear out of the exhaust, and stray gusts of wind forced the stove to back up a few times. Still, I am VERY impressed with the thing. Once up to running temperature, it has the cleanest smelling exhaust that I have experienced yet! The exhaust temperature is VERY low, low enough to measure with a compost thermometer (I bet), which is the only type I have (I'll do that the next time I run this stove).
It seems, Peter, that the bell may be somewhat undersized. The fact that I am getting SUCH good results, on a warm, windy day, outside, with a 7 foot chimney (from the floor) is an indication that I can push it farther. If this were indoors, With a nice tall chimney, on a cold day...
Yes, it IS easy to make the bell taller.. I'll have to make some more adobes.
Sunday.. Woke up late and took coffee with the stove. Started the stove around 10:00 AM. Fed it off and on till about 4:00 PM.
Experienced occasional smoke-back at fairly regular intervals. The firebox is tight, being a 6 inch stove; coals pile up, partially block the burn tunnel transition and if fresh wood is added on top, it will climb up the wood and smoke out the feed. The fix is to let the pile of coals burn down somewhat before adding fuel. Todays fuel was roughly one (plus a little) milk-crate full of 1"x1"x6" redwood/fir construction waste.
The fire started easily (the stove is now completely dry). After an hour and a half, the bell became warm to the touch, it's temperature is remarkably well distributed (to the touch), very little variation from bottom to top. I expected it to be noticeably warmer at the top, while there is some difference, it's subtle. Exhaust temperature remained low throughout the burn, there was some condensation present. It was foggy last night and I think that since the wood I'm using is piled on the ground, under redwood trees, it got a little damp.
Experienced occasional smoke-back at fairly regular intervals. The firebox is tight, being a 6 inch stove; coals pile up, partially block the burn tunnel transition and if fresh wood is added on top, it will climb up the wood and smoke out the feed. The fix is to let the pile of coals burn down somewhat before adding fuel.
May I suggest an (at least partial) fix to the smoke-back problem?
According to the pictures, there's some space between the adobe and feed tube at the front and back. Scratch some abobe away left and right of the tube, so there's equal room all around and about the same depth. Cut a steel plate to cover this hole and some more, cut a hole which fit tight over the feed tube plus a smaller hole in front of it. This smaller hole preferably somewhat further away from the feed.
Maybe you have to do some more scraping at the surface of the adobe bricks to allow the bigger rectangle hole in the plate to slide a tiny distance down over the feed, 1/4" would be adequate. Finally, cob the plate in around, as airtight as you can achieve.
When all is done properly you've created this: the air required for the p-channel is entering now in front of the feed through the smaller hole, will stream around and enter down at the back of it. This is the actively cooled feed tube, it will help a long way to prevent smoking back. As a side effect, it will pre-heat the p-channel air considerably, very good for combustion as well.
For pictures of this plate and its position see the thread "6″ Dragon Burner masonry heater using chimney flues".
edit: The plate needn't to be heavy gauged steel as long as it is flat enough for the purpose. I've been using the bottom of a cooking oil pail, did the sizing etcetera with tin snips. Maybe you've some top of an oil drum lying around, doing nothing uptil now?
edit2: Of course, you could leave out the smaller hole and carve a channel straight out. That would be doing the trick as well, as long it is opposite thr riser, i.e. not to the side.
Last Edit: Aug 5, 2013 9:54:09 GMT -8 by peterberg
Hey Kata! Good to see you here. Welcome! Yeah, I moved the chimney. It fit my idea of what the "model" should look like. The thing is supposed to fit on the stove-pads that you see in older houses, all over the coast here. Most of them have a chimney jack, smack in the middle (above).
Fun seeing the DragonHeater shippable casting and your site-sourced castables / adobe work coming together! Very tidy design, I must say. Any rules of thumb emerging regarding the size of bell to combustion unit?
Oh - one other safety note: Love this fits-on-existing-brick-pad idea. For an actual install on an existing pad, you'd want to check what's under it before building.
We pulled one up here a while ago and found that it was bedded in old-fashioned tarpaper. Still sticky, still highly flammable. (Much more tar than the stuff we bought for the roof, or it had maybe gotten gooier with heat over the years...)
Not sure why anyone would put tarpaper under a hearth. To "protect" the wood floor from ash or something? Part of the original moisture detailing of the wood floor in this mostly-log cabin? Because the guy doing it learned to do that on patios to stop weeds coming up, so that's how he always lays brick pads? He's probably 40 years gone and 2 owners ago, so we'll never know.
Anyway, it was a surprise, and I'm super-glad we checked before building on top of it. Depending on the heat output of your burn tunnel / lower firebox, it could be a really nasty thing to discover by accident. I'd highly recommend pulling up at least one or two bricks to check what's underneath, and re-lay the pad if needed.
Good point, Erica.. Alternately, the combustion area could be lifted, insulated better and an air-gap added under that. I wouldn't worry (much) about under the bell floor but it could be treated in the same way.
It's finally time to move the stove to a new home. It has performed well and proved itself admirably. Without putting a fine point on it, I think that the barrel/bell sizing combination is just about right. More testing would be needed to find the breaking points there.
Anyhow, I've torn into the stove and removed the heater core. The vermiculite board heat riser is looking good, though it's gasket has become soft and very easy to break (which I've done, reduced it to a few pieces). The tape burned off very nicely, no gunk left behind. A large crack has developed in the fire-box. Not a problem as long as I'm careful with it and support it properly while moving and in it's new home, etc.
Thinking back to discussions regarding the EPA tightening restrictions on fine particle emissions... This set up with the unfired adobe bell could be an ideal candidate for testing. I wonder what it would take to get someone in your area to run those kinds of tests. Perhaps Matt Walker has met someone in DC who knows someone not too far away (?)
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deadstarsstillburn: The people over there recommended either a 6" batchbox or an 8" J-tube. I don't know what those are but am going to try to figure that out. What I need is a blueprint that I can scale to fit the need for my house. I have something likne 5000 square feet
Oct 21, 2020 6:53:00 GMT -8
deadstarsstillburn: but I do not need to heat all of it by any means. probably only need to heat half of that, maybe less.
Oct 21, 2020 6:53:15 GMT -8
deadstarsstillburn: moreover, the house has 3 storeys (large attic) so I assume if I get very efficient heating on the ground floor, that will go a long way toward heating the upstairs as well, no?
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