kiln chimney questions

[electramom]

I am building a kiln that's body is a Seattle pottery supply 25-inch oval, I am turning it into a gas kiln vs the electric that it is now. How do I calculate the size of the chimney that I am creating? I am probably using fire brick. I figure the brick near the opening needs to be the kind that can withstand the kiln temps, can the rest of the chimney be made with the lower temp fire brick?  There is a price difference and the difference of shipping as well. 

[Hulk]

Hi electramom!

Downdraft or updraft?

My guess would be that a chimney would be necessary if you're planning a downdraft design, for the flue would provide the pull required to move air down through the kiln.

An updraft would just vent at the top of the kiln?

If your chimney is for directing the effluent out of an indoor setting, hence, perhaps a long run, then you might consider insulated flue pipe.
...or setting up the kiln away from the Studio.

Mainly I just wanted to say "Hi!" and ask if you're doing up or down draft, so the kiln experts may be able to provide helpful information for you.

Edited February 4, 2023 by Hulk
shpellin'

[High Bridge Pottery]

If I remember right it's 2 x internal height + half internal length. Not sure it holds up for kiln conversions, I tried a chimney around that size and it didn't seem to do much.

 

Had a look in the kiln book and he says for natural draft kilns 3 x downward pull + 1/3 x horizontal pull so I hadn't remembered quite right.

Edited February 3, 2023 by High Bridge Pottery
Remembered wrong

[neilestrick]

What type of burners- venturi or powered?

[electramom]

https://www.amazon.com/Regulator-Propane-Furnace-Foundry-Blacksmith/dp/B07Y364HWD/ref=sr_1_5?crid=JLNEED8FK1CJ&keywords=kiln+burner&qid=1675472976&sprefix=kiln+burne%2Caps%2C442&sr=8-5

its a double burner like this. and it will be fired to cone 6 and will be propane fired.

[electramom]

Thank you for the calculation.  my husband says cross draft or downdraft we are still finding that out. downdraft was the original plan but hubby is looking at cross draft because of the chimney.

[Bill Kielb]

11 hours ago, electramom said:

 

I am building a kiln that's body is a Seattle pottery supply 25-inch oval,

 

Since this is an oval Kiln and likely not very tall its firing area will likely be limited by burner space and draft strategy. Flue / chimney sizes are most influenced by total btu and type of burner(s). Do you have an existing design you are patterning this after? I assume it will remain top loading which will influence placement of the flue a bit. Can you post anything on dimensions, concept, btu …..  it will likely spark more ideas here.

[neilestrick]

Have you confirmed that the BTU output of the burners is enough for your kiln? What sort of safety system will you be using- Baso valve?

Conversion kilns of this type generally have a lot of issues with firing evenly or reducing evenly or even getting to temperature. The biggest issue is that people try to utilize the interior space like they would with an electric kiln, which doesn't work well at all. You have to have more space for air flow, so smaller shelves are usually needed. One of the best conversion designs is THIS ONE. With an oval you have the advantage of being able to make one end the flue and still have a fair amount of stacking space.