Fire Wall

[filb972]

Hello, I am finally done bricking the 2x4 evaporator and I'm down to doing the firewalls. I am going to put 2 walls in, one at the step and one toward the flue. How much space would be require away from the flue collar opening on the end for a good draft. I was thinking about about 5"or so. Also how much space should be left below the pan?
Thanks

[maple flats]

Is that a 6" stack? If 6" you have about 28.26 sq", at 2' wide , I might think 2 or 3" max from rear of firewall to start of stack flare. In between these 2 walls, fill it with vermiculite and cap with half bricks or refractory. I capped mine with a combo, I laid half bricks loosely then spread dry refractory over them. Then I lightly brushed to move the powder into the cracks. Next I misted the surface lightly. After a few days I misted a little heavier. After a 3rd time, I let it set a day, then I added water to the pan and built a small fire. Each day I again added water to the pan and fired a little harder. On the 3rd or 4th day I fired it enough to just start to boil. After it cooled each time, I drained the pan and put a insulated blanket over top. I then placed a 100W light bulb in the firebox to prevent freezing and let it set until the next firing. After my boil, I just left it until the season started. This gradual heating was to set or cure the refractory. Once cured it no longer needs to be protected from freezing.

[filb972]

Thank you for the advice. I was going to leave about an 1 1/2" between the pan and firewalls. Do you think that is that too little?

[maple flats]

I would reduce that to 1" if it is a flat bottom pan, and if it has flues reduce the space to 1/4". You need to force the heat to the pan.