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Post by spinal on Aug 9, 2012 8:43:56 GMT
For a variety of reasons, I don't want my oven to have a conventional chimney... One being looks, the second being planning permission (from my understanding, if the top of the oven is higher than my wall, I may need planning permission). (Also, after looking for hours, it seems that as long as the oven isn't classified as a "building" it's exempt from the clean air act, which would be a pain as my entire borough is a smoke control zone.) So I have an idea or two - but need to somehow duct my "exhaust" from the front to the back - otherwise I'll end up in the chef's face! One solution would be the flexi-foil-metal ducting - but not sure how well that would hold up to the heat. Plus, it would require quite a lot of insulation... So I was thinking chimney flue liner - which I've seen on fb "split" in halves, which would work quite well (look at the pics on this 81" beast: www.fornobravo.com/forum/37/81-inch-first-build-first-post-11354-14.html#post91905 ) That said, try as hard as I might, I can't find any websites selling this... ideas? I'm about to resort to new clay sewage pipes in my head... M. |
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Post by faz on Aug 9, 2012 8:58:32 GMT
I would check that your assumptions on planning are correct, as they seem a little peculiar to me. Failing that, put up a taller fence!!
i am not sure whether sewage pipe will tolerate the heat, but you could alway light a fire and put one on and see what happens - any cracking or spalling.
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Post by faz on Aug 9, 2012 9:00:08 GMT
And as an afterthought, the more bends you put in your flue the harder it will be to get a decent draw, especially if you don't have a reasonably long vertical length which will produce the draw - like the one in the FB thread you linked to.
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Post by spinal on Aug 9, 2012 9:14:04 GMT
My idea was to have a diagonal flue as a pose to a vertical one... in theory, heat should still raise causing the air to move... (in theory  ) The horizontal lenth would be about 2m long... but with a vertical displacement of only 1m or so... In a worst case scenario, I would fit a removeable metal flue to the end... let me see if I can upload a quick sketch of my idea (at work, so really shouldn't be fiddling with this ) M. |
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Post by tonyb on Aug 10, 2012 8:50:54 GMT
The longer the pipe and no of bends will reduce the flow due to fluid dynamics. Small as in not tall flues aren't very efficient especially in the early stages of firing. I think the issue of planning permission/smoke control has been discussed on the forum (probably the old forum), my understanding was that provided the wfo is not integrated into a building then there were no planning or smoke control issues for normal domestic installations. There is still always the issue of nuisance, but a wfo is not more an issue than a bbq or occasional burning of waste. One solution is obviously not to have a flue at all which is not as pleasant to use but certainly wouldn't make the wfo unusable.
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Post by spinal on Aug 10, 2012 10:05:52 GMT
Right - minor modification to the plan then  It's going to have a hidden flue then anyone know how to build a pointed arch without a keystone? (or maybe with a partial keystone... hmm... need to do some thinking,....) M. |
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Post by turkey on Aug 10, 2012 10:16:43 GMT
sounds like you are talking about a squirrel tail oven, mha-net.org/docs/v8n2/wildac06b.htmwhere the actual flue is in the middel? as Tony says the flue is not required but does help firing, and by creating a draw when in operation proper you should not be getting smoke in your face as it will suck the gas out which will only be smoke untill the fire is burning well, and as the oven heats the chance of smoke reduces a lot. I dont believe planning is an issue, it would be seen similar to a brick bbq which often also have high flues to remove smoke, I have always found the planning teams a friendly bunch so if in doubt just give them a call. The gov has relaxed planning massivly so most modest things even to the house are counted as permitted development unless you are in a conservation area. I am in merton btw and they seemed fine and just pointed me to defra to check on the smoke issue as they had no idea, and given they have no idea but are the ones who are supposed to enfice it, it probably says something about it in their list of priorities  |
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Post by spinal on Aug 10, 2012 11:36:42 GMT
Nope - not a beavertail... this is for the outer oven enclosure, not for the inner dome. Insteaf of a "house" look, I'm going for a pointed dome:  Was planning on having the flue come out at rear, just under the apex. But now I'm thinking of making a vertical inner flue, then distributing it over the keystone and having holes in the keystones... will try to put a sketch together... m. |
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Post by spinal on Aug 10, 2012 12:29:11 GMT
Sketches as promised... apologies for my lack of drawing ability! First sketch:  Added a the head that I'm casting... (yes, it looks naff on a sketch)  and an idea of the internal flue/pipe. The idea is, from outside there is no flue, but the flue is inside. The hot air comes out from a selection of holes in the keystone (thinking of moulding the keystone out of concrete and putting some foam or pipe inside to make the holes... just need to figure out how to stop water entering from those holes...) Maybe having a half-pipe gutter underneath or something on those lines...  |
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Post by turkey on Aug 10, 2012 14:55:38 GMT
so its a low low dome and then a high vaulted containing structure?
the idea of holes in a keystone seem to me sounds like it will restrict the gas flow which may not be so good.
how high do you think final structure will be, and as such will it have a decent hight flue?
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Post by spinal on Aug 10, 2012 16:21:16 GMT
Total height I'm thinking at around 50ish inches (15" dome (with a 10" door) (yes, I'm becoming saner) + 35" for the flue/chimney) - it wouldn't be a small structure... but it will be (just) under the height of the wall... Holes in the keystones becomes a "missing" keystone brick every second brick, with a concrete sloped gutted underneath to stop water. Flow shouldn't be an issue then... My issue now is how to get the loose vermiculite into the gap - can't be before the keystone goes in or the whole thing will fall apart.... but after it's all locked in May need to pour from the side... hmmm M. |
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Post by cannyfradock on Aug 10, 2012 16:56:09 GMT
H
That looks very impressive. Can't quite get my head around the total concept, so shall read through your posts a few more times.
Not sure of your construction method, but if you want to fill a void with loose vermiculite......it doesn't have to be crammed to the outer surface for it to work...it just needs to cover the inner dome by at least 4".
The 10" door (if that is the entrance door) is far to small. My first Pompeii I made the door 14" with a 12" pizza in mind. Through trial and error I now know the minimal width for a door is 16" for it to be practicable. I have since pushed that size up to 18"...on a 36" internal diameter Pompeii. Still waiting for results to come back to see if 18" still functions correctly.
Terry
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Post by spinal on Aug 10, 2012 17:08:48 GMT
10" is the height of the door, about 2/3s of the height of the dome. Width will be... no idea really! Probably 60% of the 40" diameter, so 24" or so... maybe a bit smaller if that's the consensus I'm (finally) picking up the vermiculite tomorrow... then it's waiting until the end of the month so I can order fire bricks, HAC, fibre blanket and some vermiculite board... m |
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Post by cannyfradock on Aug 10, 2012 17:32:35 GMT
....oops.......sorry M, now I am with you.
I've done a lot of research into finding an equation.....like the 63% rule of arch to dome height which relates to the width of a door in relation to it's diameter......I'm still looking.
I have also tried to work this out mathematically, but the pure nature of these beast's drawing in "new" air, expanding it and drawing it over the dome to it's nearest exit......the vent if calculated well.....can't relate to the lower echelons of the internal arch, so a calculation of an equation to door width to diameter ratio must have different value's.....oh dear.....I'm totally confused now.
Terry
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Post by turkey on Aug 10, 2012 20:11:27 GMT
I see what you mean on the flue now, I would also add that you do get soot build up in the chimney so these holes would need to be of decent size. I like the bold enclosure design but still not sure on the flue.
what is the main reason to have it vent out as it does, are you trying to increase the dissipation of the smoke or is it purely aesthetically motivated.
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