building a gas kiln help

[electramom]

I just got a 25" X 30 inch oval kiln. I am changing it from its broken electrics to propane. I am trying to decide what size bottles to purchase and could also use a little help deciding how many burners it needs, my husband thinks maybe four but I worry that might be too many. I could also use reccomendations.

[Bill Kielb]

Depending on height that might be a tough shape. As a practical matter though I would say first find out how much power you will need in Btuh. So let’s say if we start by taking all the watts it’s rated at now and multiply by 3.41 to convert watts to btu. A 10,000 watt cone 6 kiln in theory needs 34,100 btu to heat equivalently to cone 6. But wait, gas kilns need a flue and likely lose 50% or more  of their heat through the flue. So in the example above you could size it at 150% - 200% or more to get burner sizing as the gas is infinitely adjustable so getting less heat just means dropping the gas pressure a bit. Then once total btu is known work backwards for number of propane bottles likely needed.

As I said, this might be a tough shape to design in gas, I would refer to similar kilns already converted and see how many burners they used. Once you have a total energy needed it is easy to divide that up amongst smaller burners. If you intend to fire to cone 10 then that will cost you a bunch more energy. I think Olympic makes a round updraft prox 30” tall that uses 2 burners about 250,000 btu to get to cone ten. You likely will be in this range for energy but 4 small burners at 30k-50k  each may even things out and a minor change in orifice size makes this easy to start conservatively at 30k and ramp up to 50 k or more. More small burners will provide better control at the beginning of firing when very little energy is needed and more consistency when oxidizing or reducing.

so approximating all that above, 1 gallon of propane yields approximately 92,000 btuh. Pick a low and high consumption per hour, let’s say 50k btuh (low) to 150k btuh (high)  means 0.5 gallons to 1.6 gallons per hour for let’s say 8-12 hours. A 20# grill type tanks hold 4.6 gallons full. A 40 pound tank is 9.2 gallons and so on. As your firing progresses you will consume more gas and the tanks will cool or ice which often means you will want to err on larger than smaller or have spare tanks ready as iced tanks will have reduced output just when you need it most.

Double check my math.

Edited October 2, 2022 by Bill Kielb