Polydeuces Posted December 8, 2017 Report Share Posted December 8, 2017 Hey y'all -- So I have an old Jenken sitter kiln I got from a retired potter (along with my other equipment). Earlier this year I converted to fire with gas (downdraft), using a homemade cast-iron burner with a squirrel-cage fan. I don't have any issues getting it up to temperature, but I have noticed that it is significantly cooler closer to the bottom of the kiln, and it feels like an unacceptable portion of my work is not getting the heatwork it needs. I don't load anything on the floor of the kiln, but have some bricks to help steer the heat. I've tried a couple configurations, but every time I fire there are very significant differences across the strata of the kiln. I'm pretty frustrated and can use some guidance. Some details The burner sits underneath the kiln and fires upward into the kiln, close to its edge. There is an external chimney made of soft firebrick. The flame enters the chimney through a port on the side of the kiln, which is on the other side from the flame's entry, floor-level. I've cut a little bit off of the shelves I'm using to allow for the heat to move unimpeded. I'm not an expert by any means -- my initial thoughts are that the heat is moving past the first shelf too quickly, or has no reason to linger there. I'm considering placing the second shelf offset, so as to block the flame and persuading it to move around toward the top of the kiln, sort of like a spiral. I'm concerned about possible crackage, though, or any issues I might not be foreseeing. Just curious about any thoughts that y'all might have. I understand that gas kiln conversion problems are probably tricky to diagnose, but I'm wondering if there's something elementary I could try that I've overlooked, or some kind of general troubleshooting checklist for those of you who have more experience tinkering with this method than I do. thanks! Kevin Link to comment Share on other sites More sharing options...
neilestrick Posted December 8, 2017 Report Share Posted December 8, 2017 How high off the floor is the bottom shelf? How many cones difference is there between the top and bottom shelf? If you're using standard kiln shelves that are made to fit that kiln as an electric, then they're probably too tight for good air flow as a gas kiln. Link to comment Share on other sites More sharing options...
Polydeuces Posted December 8, 2017 Author Report Share Posted December 8, 2017 Hey Neil, thanks for the response. Between the floor and the first shelf, the height is that of a kiln brick laying on its side (narrowest & longest face on the floor) -- 4.5"? I haven't measured the floor or the very top, but the first (loaded) shelf compared to the third seems to be close to a one cone's difference. I am using standard shelves -- do you mean they ought to be more like hollow core shelves? Link to comment Share on other sites More sharing options...
neilestrick Posted December 8, 2017 Report Share Posted December 8, 2017 One cone difference isn't bad at all for a kiln of that type. It's really good, in fact. Even in a regular gas kiln, 1/2 a cone is acceptable. But I understand you wanting it to be better. Not hollow core- smaller. More space between the shelves and the walls, to allow for better air flow. Normally, the shelves in an electric kiln are only about 1.25" from the wall. That's fine in an electric, because air flow isn't an issue. That's fairly constricting to air flow in a gas kiln, though, where air movement is everything. You're not trying to hold the hot air in, you're trying to have it come in, heat the work, then move out to allow for more hot air to enter. If you have half shelves, stagger them rather than putting two together to form a full shelf, and keep each one an inch further in from the wall than usual. Link to comment Share on other sites More sharing options...
Polydeuces Posted December 8, 2017 Author Report Share Posted December 8, 2017 Whoa! Seems I had it backward. I had some full-sized shelves that I cut a little to allow for the upward flow -- I'll take a little bit more off, I think. Thanks for your help! I'll post some results when I get around to another go. Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted December 8, 2017 Report Share Posted December 8, 2017 I took the side off a shelf in my kiln conversion so the flame had some space, also been considering taking the same off the other side. I don't exactly remember but I think it's 0.5-1 cone hotter at the bottom. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted December 13, 2017 Report Share Posted December 13, 2017 How do you regulate the air volume on the squirrel cage blower? I made some burners with squirrel cage blowers and screwed a metal disc over the intake that could adjust the intake on the blower. A longer flame with less air may help even it out. Marcia Link to comment Share on other sites More sharing options...
neilestrick Posted December 13, 2017 Report Share Posted December 13, 2017 8 hours ago, Marcia Selsor said: How do you regulate the air volume on the squirrel cage blower? I made some burners with squirrel cage blowers and screwed a metal disc over the intake that could adjust the intake on the blower. A longer flame with less air may help even it out. Marcia I always used magnetic business cards for intake covers. Link to comment Share on other sites More sharing options...
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