How much room under flat pan

[Bricklayer]

I've got a 2x5 divided flat pan. I'm just insulating my arch and was wondering what a good distance between the pan and the top of the ceramic blanket on the ramp. I know with flus it as tight as possible without touching but with a flat pan I'm assuming you need a little room for the gasses to pass by the pan

[psparr]

You want the same surface area as your stack pipe. If it's a 6" stack then about 3/4-1" if 8" then 1-1/2"

[Bricklayer]

It's a 6" stack. Was supposed to be 7" but my math didn't work out on my homemade stack base. So 6" was biggest I could fit in. I've got 1 1/4" as it sits right now to the bottom of the pan with 1.5" arch board and ceramic blanket and firebrick. I will try that and if it doesn't work I can put another layer of blanket. I'm a little worried 6" stack won't be enough. I've got a blower so it's forced draft but not sure if it will be enough once it gets going. Should I drop it down to a couple inches after the back of the pan under the stack?

[psparr]

Try it first, but probably do better closing it up a little.

[maple flats]

If it dosn't work, just add more stack rather than trying to change things mid season. More stack will usually help. Be sure to brace it if it gets unstable. The minimum stack is 2x the evaporator length, but adding 2 or even 4' can often work wonders.

[Big_Eddy]

You want the same surface area as your stack pipe. If it's a 6" stack then about 3/4-1" if 8" then 1-1/2"

I recommend 1.5x the area of the stack pipe. You want a restriction where the arch transitions to the stack to slow the gases down and keep a bit more of the heat under the pans. Same reason why some people place a brick in the flame path at the end of the flue pan.

[tcross]

i have a 4x4 flat pan I boil on with a home made arch. I have a 8" (12') stack and a blower... I leave about 2 1/2" under my pan after the fire box and my rig roars! I have a few chunks of brick/cinder block in front of the stack and at the end of the ramp to create "turbulence"... seems to do the trick! just my experience!