Wildcat Creek Brick Company

Thursday, January 14, 2010

Wood kiln modifications to add crossdraft flame flow done.

Its been below freezing since Christmas here, so the snow and ice have built up alot outside. Though cold its beautiful too. Looking out my back door across the porch and backyard to the kiln barn.

I reworked the kiln chamber floor as best as I can to reflect Peters crossdraft suggestions. Im still thinking of ways to improve my ash pit which is undersized and difficuct to empty. The entrance flue vent to the chamber is now at the front while the exit flue to the chimney is at the rear.

Looking foward to trying this out as soon as I get the needed firewood gathered up!


  1. Hi Richard,
    It looks beautiful at your place with the snow and ice. Well done making the change to the kiln chamber, it will be interesting to see how that changes things when you fire. You are right to try and improve the ash pit if you can, the deeper the better really, It really helps if you can get a good flow of air through there without it blocking up.
    Funny thing is that I am getting kiln building urges at the moment, and may do something about it soon (I can't put the urges down to spring, as it is supposed to be summer here... even though our summer this year has been only marginally warmer than the winter... and not nearly as sunny!). I'll post any developments of the new kiln on my site if I get round to building one, I've got this idea floating in my head for a down draft fire box and a cross draft chamber that I would like to play with. If possible I would like also to make a heat exchanger to preheat the air that comes into the firebox, apparently there are considerable gains to be made by doing this, but few kilns make use of it due to the added complexity.

  2. It would be great to see another of your kiln builds Peter! You can count on me watching for those updates in your blog.

    Unrelated question for you: I found a large pile of coal in a storage room in the basement of my rental house. They must of had a coal fired boiler for heat years ago. I am kicking around the idea of an experiment. What if I fired my kiln with the coal next time to see what happens? I read that coal can get much hotter than wood alone. Not sure what will happen but I have plenty for one firing of the kiln. The price is right too. Free. Whats your opinion? Ever heard of someone else trying this?

  3. Hi Richard,
    I haven't used coal myself, but I do know of potters that have used it very successfully. Coal certainly has a lot more energy locked up in it than wood. Really the main thing is to sort out an appropriate grate. A low grade lignite type coal can be fired on a grate that is fairly similar to a wood fired one. You would use metal grate bars that were probably spaced only an inch and a half apart at the most. You would need a long poker, probably with a hooked over end, to break through any ash or clinker that might try to block the grate. An article I read about firing low grade coal recommended a low pressure blower feeding air into the firebox below the grate. Some air was necessary for the coal to burn efficiently, but too much would cause clinker to build in the grate and block the passage of air. You could fabricate a suitable grate from steel. It would look like a ladder with really close rungs, and it would have feet to lift it to a suitable hight in the firebox. A metal grate like that could be pulled out of the firebox once top temperature had been reached. This would prevent it from warping, as it might do, if it were left in the firebox when the kiln was clammed up.
    High grade coal (the really black bituminous stuff), needs a different style of grate. Most were made from iron bars that went lengthwise into the firebox, and were angled steeply down at the front so as to allow lots of air to come in under the coal. The steep angle also allowed the coal to be broken up with a poker if the grate blocked. This style of grate worked with natural draft.
    I have a small heap of coal here too that I look at with longing....


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