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Kiln Shed Roof - Distance From Kiln

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#1 Kristin_Gail

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Posted 31 October 2013 - 09:07 AM

After much fretting and planning, we finally moved my 800-lb kiln from the driveway to its little concrete pad in the backyard. We're now in the process of constructing a little shed around it.

The corner posts are in, as are the trusses for a single-pitch roof. The walls (I have to have walls, to keep out the snow - there will be large removable sections for ventilation during firing) are 3' minimum from the kiln. For at least 12" around the chimney there will only be the metal roof, no trusses or strapping.

But after the kind husband put the trusses up, I realized - they look really close to the kiln. Clearance is about 28" at the closest point.

Do you think I could keep it this close, but put some sort of a heat barrier up there? Durock with an air space? If we need to rebuild it, how much of a clearance would we optimally have?

If it matters, this will be a crossdraft propane-fired soda kiln. With a bit of wood, as well.

And I know the photo is difficult to decipher - it's tight quarters back there; difficult to get a proper shot.

And I'm incredibly thankful, as always!

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#2 neilestrick

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Posted 31 October 2013 - 09:49 AM

That looks pretty tight. The problem is that the heat from the kiln will dry out the wood, lowering its flash point. And with the likelihood of flames coming out of the exit flue, it's really not the best situation. Ideally you need a metal hood over the kiln with a flue going through the roof. The temperature at the ceiling directly above the kiln flue will still be a few hundred degrees. Any chance you can swap out the wood trusses for metal?


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#3 Kristin_Gail

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Posted 31 October 2013 - 10:12 AM

Thank you so very much for such a quick reply!

A friend has some metal 2 x 4s we can have, but my husband isn't a fan. Basically he doesn't understand where we'd get larger ones, and then how to use them. What would we use for strapping between the trusses? Smaller pieces of metal, but what are these called and where do they come from? I can't answer his questions because I don't know to whom I should direct my questions. They don't sell this sort of thing at the Home Despot, he tells me?

#4 Mark C.

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Posted 31 October 2013 - 10:31 AM

Call around at materials suppliers  and ask for for metal studs and components. These are not sold at big box stores. The larger beams and struts that hold them are all sold at the same places.. You just use different screws than wood construction. I would use these beams around the area above kiln only and use the wood rafters on the outside still. You will need as you said to keep all wood some distance form your chimmey

Your husband does not like metal studs as they are harder to work with and are wimpy until braced.

Mark


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#5 neilestrick

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Posted 31 October 2013 - 02:22 PM

I don't think metal studs will work as roof trusses, as they are not designed for horizontal spans. You will need to use angle iron or something like that. The wood trusses you have will work fine if you have a vent hood over the kiln.


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#6 Mark C.

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Posted 31 October 2013 - 03:19 PM

Any sheet metal place can fabricate the hood-most are made from galvanized metal and these last -some a good while-the better ones are stainless and last almost forever-you can also just put stainless in the high heat area and galvo in the rest as  friend did on his last month on a Geil Kiln.

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#7 Marcia Selsor

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Posted 31 October 2013 - 04:16 PM

I agree with Neil and Mark. Put a hood between the heat and the roof.

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#8 Mark C.

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Posted 31 October 2013 - 08:14 PM

Refresh my old memory Are you building a chimney for this kiln or is it an updraft?

If its a downdraft then just add a heat shield over kiln and keep plenty of room from stack to wood- You can add some heat shields as well. If its an updraft then the whole kiln hood makes the most sense.

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#9 Kristin_Gail

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Posted 01 November 2013 - 06:32 AM

I am grateful.

I had intended this thread as something I could hand to my husband, saying, "Look! The experts agree with me! It has to be metal!" Which you did - but ah, look now. A new idea. The hood ...

This is a top-loading kiln. The fabricated hood would cover the entire top of the kiln - overhang on any sides? - and hang on chains somehow? How far would it need to be above the kiln and away from the roof?

It is a downdraft (technically a crossdraft) with an 8.5' chimney through the roof. (I'll be back here in a week to ask about the chimney - my guess is y'all will have changes to my plan on that one, too.)

#10 Kristin_Gail

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Posted 01 November 2013 - 06:38 AM

I'm seeing now. A vent would be conical or pyramid-shaped, and vent the heat outside through a tube. But a heat shield - that would not need to vent, correct? It would just be a piece of metal (flat? pyramid?) suspended above the kiln? Where would the heat be deflected? Just out into the room?

#11 Kristin_Gail

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Posted 01 November 2013 - 08:21 AM

And, if the heat shield need only be flat, could I use one of the many spare pieces of metal roofing I have lying about? Suspend it from chains a particular distance above the kiln whenever it's firing? If flat isn't proper, I could use two pieces with a roof cap to make a triangle ...

#12 Biglou13

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Posted 02 November 2013 - 03:15 AM

A hood system really needs to vent to outside. Think kitchen here.

A flat piece just redirects the heat, smoke, embers..... And sure as that stuff moves away from kiln it looses temperature/ energy. But you spoke of using multiple fuel sources aka wood. So my 2 cent vote is for hood system.


Google images vent hood for kiln

The cone shaped one looks easiest to build. Basically cone (truncated cone).

Or even better build chimney , through roof. Yeah fire bricks air cheap. I've seen transition from fire brick to ceramic chimney pipe a cheaper solution. I asked the question before but no one had answer, How far up or past kiln can you transition from fire bricks to cheaper ceramic chimney pipe or metal or to non fire brick?
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#13 Kristin_Gail

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Posted 02 November 2013 - 07:37 AM

A hood system really needs to vent to outside. Think kitchen here.
A flat piece just redirects the heat, smoke, embers..... And sure as that stuff moves away from kiln it looses temperature/ energy. But you spoke of using multiple fuel sources aka wood. So my 2 cent vote is for hood system.
Google images vent hood for kiln
The cone shaped one looks easiest to build. Basically cone (truncated cone).
Or even better build chimney , through roof. Yeah fire bricks air cheap. I've seen transition from fire brick to ceramic chimney pipe a cheaper solution. I asked the question before but no one had answer, How far up or past kiln can you transition from fire bricks to cheaper ceramic chimney pipe or metal or to non fire brick?


Hi Biglou - I am building a chimney, it's 8.5' high, will go through the roof. That's why I wonder if perhaps just a heat shield, without a vent, would work.

#14 Biglou13

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Posted 02 November 2013 - 11:11 AM

its a single slanted roof.  i think heat sheild / barrier will be fine.

single hanging sheet is 2 levels of insulation other than kiln , sheet of metal, circulating air between metal and structure.

id get a cheap infrared thermometer and check while kiln is firing along with ocassionally check wood. 

 

sorry to add more concern but how much clearance are you planning chimney to roof opening?  id be worried about that tolerance.  there is reference to this in an older post.

 

im excited to see you progress

 

(im glad i dont live close enough to you to move and 800 plus pound kiln)


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#15 neilestrick

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Posted 02 November 2013 - 11:43 AM

Your chimney can be right against the metal roof. That's not a problem. But put some fiber board insulation along the roof trusses near the chimney. 12" is not all that much clearance.


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#16 Kristin_Gail

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Posted 03 November 2013 - 09:17 PM

New developments:

1. Incredibly patient husband has moved the beams up 8".

2. I visited a wood-fired potter (a handful of potters do exist here; they're just an hour away) and noted a charred beam on her kiln-shed roof.  Her current chimney, bricks + castable, was not the culprit.  Rather, it was the first chimney, a bare culvert pipe.  Noted.

 

Future efforts:

1. Will build a heat shield from galvanized roofing.  If I find during the first firing this doesn't do the trick, will have one fabricated.

2. Will figure out what fiberboard insulation is, and get it where it needs to go.

3. More tree limbs need to come down than previously planned.



#17 Biglou13

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Posted 04 November 2013 - 09:22 AM

Cut tree limbs = fuel for kiln

There are different kinds of insulating fiber board.

The expensive stuff is ceramic fiber board, I've see it used in kilns. I think this is over kill. To insulating fiber board used in home building.

I really don't think its that technical. Some material. Slightly refractory that will protect wood for the heat of the chimney.

I'm thinking cheap... Four trapezoidal (tin roof) pieces attached together. Making a "mini" hood. Around roof opening

I'd also have some mud ready during firings to patch leaks in brick.
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#18 neilestrick

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Posted 04 November 2013 - 11:03 AM

By fiber board I mean the stuff made for kilns. You don't need the expensive high temp spun silica stuff. The stuff rated for low fire will do just fine. Insulating board for home building is a styrofoam type material (polyisocyanurate, to be exact), which insulates well in walls, but it not rated for high temps. It would be more of a fire hazard than the wood. You need something that can handle several hundred degrees. Go to your local fireplace store and see if they have something.


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#19 Kristin_Gail

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Posted 04 November 2013 - 05:05 PM

Hi Pazu -

 

You can see the details of the kiln in this thread.  After a few changes along the way, I've ended up with two MR-100 Venturi burners.  This is in my backyard, in town, so I do have electricity. 



#20 Kristin_Gail

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Posted 04 November 2013 - 05:08 PM

Thank you so much, again, Neil.  I've just discovered the clearance around the chimney is only about 9" ... Geesh.







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