Rupsa Nath Posted January 13, 2020 Report Share Posted January 13, 2020 Hi, This is the first kiln my husband and I built. The model we followed to the letter is of Joe Finch, as he explained in his book, "Kiln Construction: A Brick by brick Approach". We have fired this kiln 3 times so far, and every single time it has gotten stuck at 550-600 degree celsius. About the Kiln: The Gas Kiln has an inner dimension of 1 cubic meter. The wall is made of regular insulated firebrick + 4" ceramic blanket +outside layer of firebrick again for more insulation. It is a downdraft kiln with two burner ports on either side. Our chimney is about 7 feet tall and the exit flue is equal to the area of the burner ports. Burners: We initially did two firings with small burners (model S20) with a Btu of 30,000-83,000 per hour. And the next model (S80) we took for our third and last firing with a Btu of 120,000-336,000 per hour. I have attached a picture which has the list of burner models so you can see all their specs. Gas cylinders: In India for commerical firings, we get 19kg LPG cylinders, and we are using two of those simultaneously for our gas firing. To keep the pressure from falling too low, I douse the cylinders in room temperature water when they start to ice up in the bottom. For all the three firings we have done, the temperature always slowed down at 560 degrees celsius, and then stuck around 580 degrees celsius. The first time we kept firing for about 3-4 hours, but there was no progress, and the last time we stayed at the temperature for 1 hour before calling quits. I have added the firing schedule below for the first and third firing so you can see how the temperature had risen. All the numbers mentioned are in celsius. First firing (Sunny day, Third firing (Sunny day, not much wind) less wind) 1.30 pm 82.1 11.47am 215 1.51 pm 191 12.05pm 364 3.32 pm 279 12.09pm 400 4.42 pm 400.5 12.28pm 533 5.36pm 504 12.51pm 588.6 6.47pm 551 1.46pm 562 7.24pm 570 7.55pm 563 As you can see, we took less time to reach 550 degrees in the third firing with our bigger burners. But all three times, the temperature got stuck at around 580. I have added pictures of our burners position as well, and we made sure they were outside of the kiln to pull in the air and burn the oxygen. Based on these figures, do you think: - Our chimney is too small in height? - Burners are not enough? -Some other factor that is stopping the temperature from rising? Grateful for any advice and suggestions. Thank you! Quote Link to comment Share on other sites More sharing options...
liambesaw Posted January 13, 2020 Report Share Posted January 13, 2020 (edited) Your chimney might set your house on fire. Here's a link to a free handout on kiln design, it has some helpful sections on calculating chimney length and combustion area for natural draft kilns. https://ceramicartsnetwork.org/wp-content/uploads/2010/05/gaskilnsfreemium.pdf Edited January 13, 2020 by liambesaw Rae Reich and Rupsa Nath 2 Quote Link to comment Share on other sites More sharing options...
Rupsa Nath Posted January 13, 2020 Author Report Share Posted January 13, 2020 Thank you for the response. I think adjusting the chimney height is what we can do as the next step to see if there is any difference. Quote Link to comment Share on other sites More sharing options...
neilestrick Posted January 13, 2020 Report Share Posted January 13, 2020 Is the top of the kiln just those shelves? Quote Link to comment Share on other sites More sharing options...
Mark C. Posted January 13, 2020 Report Share Posted January 13, 2020 (edited) Looks like the chamber is all lined with fiber.Then the shelves cover the fiber? I would suggest a taller chimmney to induce more draft. Do you have a damper in chimney to control draft flow? I did not see one in photos? Edited January 13, 2020 by Mark C. Rae Reich 1 Quote Link to comment Share on other sites More sharing options...
Rupsa Nath Posted January 13, 2020 Author Report Share Posted January 13, 2020 @nielestrick: Actually the top of the kiln is a sprung arch made of insulating fire bricks, with more ceramic blankets on top and then those shelves. @Mark C: We presently have not added a damper yet. We are currently thinking of increasing the chimney height also. Quote Link to comment Share on other sites More sharing options...
Stephen Posted January 13, 2020 Report Share Posted January 13, 2020 I realize the third pic is kind of an optical illusion but still isn't this kiln venting right into a wood side of your house? Is that safe? I mean I know heat dissipates pretty rapidly but that sure seems close especially since you are talking abut increasing it. I don't know much about kiln construction so just ignore me if my ignorance is showing through. Rupsa Nath 1 Quote Link to comment Share on other sites More sharing options...
neilestrick Posted January 13, 2020 Report Share Posted January 13, 2020 At 1 cubic meter you've got about 32 cubic feet of interior space, so you need a minimum of 500,000 btu/hr, probably more, to get to cone 10. I'm betting your little propane tanks are freezing up more than you think, especially if you're running more than one burner off a tank. You need a damper to control the secondary air draft and internal kiln pressure. Your burner ports look to be pretty big for a burner of that size. The lack of safety equipment on the burners is troublesome. They're not even mounted to something that will keep them in place. And it looks like the heat from the chimney is going straight onto the building above? Rae Reich and Rupsa Nath 2 Quote Link to comment Share on other sites More sharing options...
Rupsa Nath Posted January 14, 2020 Author Report Share Posted January 14, 2020 It seems obvious now that we need to move the kiln away from the house. Dangerous oversight on our part, which we will rectify immediately. We have been reading Olsen as well, and he too suggests a smaller burner port. We have it in mind to have a manufactured stand for our burners too. But since were just testing them out now, we thought of propping them up on bricks. @neilestrick: Do we need a damper only at the exit flue, or somewhere else as well? based on the size of the kiln and according to the calculation provided by Olsen, we got to a chimney height of about 15 to 16 feet high. Does that seem right? Rae Reich 1 Quote Link to comment Share on other sites More sharing options...
neilestrick Posted January 14, 2020 Report Share Posted January 14, 2020 Damper at the exit flue. Assuming the flue opening is the correct size, the full draft of the chimney is too much and you need to be able to damper it down. Otherwise too much heat goes out the stack, and you can't control the pressure in the kiln or secondary air draw. Rae Reich, Bill Kielb and Russ 3 Quote Link to comment Share on other sites More sharing options...
Rae Reich Posted January 14, 2020 Report Share Posted January 14, 2020 Damp at flue exit. Sounds like you're blowing heat out as fast as you're making it, maybe even using too much gas to maintain an even climb. Piedmont Pottery and Bill Kielb 2 Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted January 14, 2020 Report Share Posted January 14, 2020 (edited) 21 hours ago, Rupsa Nath said: It seems obvious now that we need to move the kiln away from the house. Dangerous oversight on our part, which we will rectify immediately. We have been reading Olsen as well, and he too suggests a smaller burner port. We have it in mind to have a manufactured stand for our burners too. But since were just testing them out now, we thought of propping them up on bricks. @neilestrick: Do we need a damper only at the exit flue, or somewhere else as well? based on the size of the kiln and according to the calculation provided by Olsen, we got to a chimney height of about 15 to 16 feet high. Does that seem right? What has been said here is correct. You will need a damper to tune this as you fire and as your temperature rises. The hotter your kiln gets the greater the draft through it. You need to be able to adjust this during firing to regulate how much secondary air you suck in. In general, the taller you make your flue, the greater the suction can be. You should be able to get a better sense of this by temporarily dampening at the top to note if there is a significant improvement, do this for test purposes only. If you confirm the requirement, then install a typical appropriate damper in your design which then will allow the total height to be fine tuned once you are able to fire to temperature. Edited January 15, 2020 by Bill Kielb Rae Reich 1 Quote Link to comment Share on other sites More sharing options...
Mark C. Posted January 15, 2020 Report Share Posted January 15, 2020 Maybe a piece of tin roofing as a heat shield next to house to defuse the heat Rae Reich 1 Quote Link to comment Share on other sites More sharing options...
Rae Reich Posted January 15, 2020 Report Share Posted January 15, 2020 Also, your chimney stack can be lengthened by going horizontal on the ground a couple of feet before rising. That would get it further from the house. I think Olson or Rhodes has an example. It's what we did on my large catenary so the stack didn't need to be so tall. Bill Kielb 1 Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted January 15, 2020 Report Share Posted January 15, 2020 1 hour ago, Rae Reich said: Also, your chimney stack can be lengthened by going horizontal on the ground a couple of feet before rising. That would get it further from the house. I think Olson or Rhodes has an example. It's what we did on my large catenary so the stack didn't need to be so tall. This can be offset but make sure you follow a decent design and you likely (at mimimum) will need a spark arrestor to top it off. It looks quite close to the structure. There are other concerns as well, rules that may state the need for it to be a minimum of 10 feet or more from a window that can be opened for ventilation. Try and research all aspects, this might not be the best placement for the kiln Quote Link to comment Share on other sites More sharing options...
Rupsa Nath Posted January 16, 2020 Author Report Share Posted January 16, 2020 Thank you everyone for your inputs. They have really helped us reassess our kiln placement and structure. We are currently moving our kiln at least 10 feet away from the house, and are going to make modifications to the existing model. Will definitely post again if we run into issues. Bill Kielb, Rae Reich and liambesaw 3 Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted January 16, 2020 Report Share Posted January 16, 2020 Please post and show us a successful fire! Looks like you are on your way with a touch more work. Rupsa Nath 1 Quote Link to comment Share on other sites More sharing options...
Babs Posted January 16, 2020 Report Share Posted January 16, 2020 If cylinders are icing at 600 deg C your rate of climb will be really affected negatively. With adjustments suggested you may be able to reduce the draw on the cylinders but it is a long way to C10.... Rupsa Nath 1 Quote Link to comment Share on other sites More sharing options...
Joe Finch Posted March 13, 2020 Report Share Posted March 13, 2020 Please email me at joe@joefinch.co.uk for my answer. Rupsa Nath 1 Quote Link to comment Share on other sites More sharing options...
Gusf Posted June 25, 2021 Report Share Posted June 25, 2021 Hi, could you please post an update to your kiln? did it go up more than 600 C ? @Rupsa Nath Many thanks, Quote Link to comment Share on other sites More sharing options...
Rupsa Nath Posted January 28, 2022 Author Report Share Posted January 28, 2022 Hi @Gusf, we dismantled the kiln completely and had to find a new place to install it. Due to Corona, we haven't managed to travel and install the kiln again. We hope to do so in these coming years and I will talk to Joe Finch for some guidance. I think our chimney on the kiln we had built before was too short and some potters have thrown around the idea that maybe the high firing bricks we got were not of good quality. I remember our temperature had gone up to 750 degree celsius eventually and the space around the kiln was hot. I have had the opportunity of firing in pre-fabricated gas kilns after that where you barely noticed the heat in the surrounding space even if the temperature was at 1220 degrees. So maybe we need to look into the issue of the brick quality as well. Quote Link to comment Share on other sites More sharing options...
Mark C. Posted January 28, 2022 Report Share Posted January 28, 2022 build a damper into your next taller chimney and let us see the photos of next kiln. Thanks for the update Rae Reich 1 Quote Link to comment Share on other sites More sharing options...
Patrick Schurt Posted June 3, 2022 Report Share Posted June 3, 2022 (edited) Hello. What I want to know is how the hell did you get a copy of Joe Finch's book lol?? I can barely find it anywhere and when I do, people want USD 500 for it!! Edited June 3, 2022 by Patrick Schurt Typos Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted June 3, 2022 Report Share Posted June 3, 2022 (edited) 16 hours ago, Patrick Schurt said: What I want to know is how the hell did you get a copy of Joe Finch's book lol? You might want to DM, I think last heard from on January 28th Edited June 3, 2022 by Bill Kielb Quote Link to comment Share on other sites More sharing options...
Matt Garrett Posted June 24, 2022 Report Share Posted June 24, 2022 I picked up a copy of Finch’s book through my library, I would start there. I just finished reading through it. I am in the beginning stages of building an exact replica of the gas kiln he built with Morgen Hall. I have the location and I have the firebrick. In a design phase now based on the amount of brick that I was gifted. Quote Link to comment Share on other sites More sharing options...
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