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[Emmauswalker]

Hello, my question is how to run a propane kiln with downdraft? I have had it stall at 2000 F. I also use a forced air (compressed) burner which is homemade. It works great until 2000 F.

[Peter Stephens]

Stalling I thinks is quite common, although generally it is not documented because people fiddle when the kiln slows and find a solution without realising the problem. My observation is that up to 2000F the kiln is heating without much reliance on the draft dynamic. After 2000 F the kiln needs a draft dynamic to increase temp. What has happened in this early stage, is that the heat is within the kiln, but the chimney or flue exit, has not been heating up, and the heat flow and the flame has not travelled up the chimney or flue. It might be thought it is merely exiting gases which go up the chimney. Really it is gases, heat, flame, and it is not merely an exhaust. It is part of the kiln dynamic. So with a stall, you may have to coaxe the heat flow and the flame to move more energetically out and up the flue. You see probably to begin with you have the flue wide open, or even closed, and now you have to give some attention to the damper (flue cover or baffle). Of course there is a some desirable degree of opening for the damper during the course of firing. But now, when it is stalling, only have a very small opening, to encourage the flame to search out and up. You could even increase gas pressure a bit. Momentarily you may have too much smoke. Have a look as best you can closely at this new arrangement, and try to see where the flame is. (Depends on type of kiln and flue) Adjust the damper to suit where the flame is now trying to go. Just for this exercise, maybe for 5-15 mins, you may have a vary small flue opening, not really suitable for your firing. But once you have coaxed the flame out and up the chimney, you can return to your standard settings. This exercise has served it's purpose, and now not only is the flue for exhaust, but is drawing the heat and flame more actively through the kiln, and you should see a temperature increase.

[Emmauswalker]

Thank you, I will try the suggestions to see if the temperature increases. Happy potting!

[Peter Stephens]

I just had another thought. The size of the exit flue from the kiln to the chimney, or whatever arrangement you have, inside the kiln at the floor, or at the back wall, may be too small. Another mistake is to not have the first, bottom, shelf raised up on small props. A rule of thumb is to have the bottom shelf in line with or above the top of the exit flue cavity. Even though you lose a bit of space it is essential for heat flow. This doesn't apply if the exit flue is connected by a channel in the floor under the shelf. Come to think of it, you may simply have a problem with not leaving enough space between the shelves and the walls.