Arch design question.

[RickinFarmington]

I am preparing to weld up a new 2 x 4 wood fired arch and have a question related to the rear wall of the firebox. Is there a significant difference between a straight wall with right angle floor that runs under the flue pan, or the ramped design that runs from the rear firebox wall to the far end of the arch? Will be using a drop flue pan.

Rick

[Kev]

proctor and cornell both have write ups explaining effeicient arch designs. There is a link on the main list of forums here

[sandman6921]

can somebody post the link, I was wondering that also, and can't find the referenced link. Thanks

[maple flats]

From experience I have found that a small ramp is needed. I originally had a long ramp and things seemed good. I then added high pressure air over the fire and the rear wall went up much farther before a very short ramp. The ramp was under the front edge of my flue pan. It boiled so hard and sap jumped so high I could not keep it all in the pan even though I had a hood over it. I lost a lot of sweet in the hood drain and had to slow the burn. This year I made the ramp a little longer and made a deflector like Leader offers on some of their 2x6's and such. This made it so I could run the fire as hot as I wanted without losing sweet. In my 3x8 the long ramp was about 2' long and started half way up from the grates to the pan. My short ramp started 4" below the pans and went just 1' tapering up to the pans and my current, good ramp starts 6" below the pan and goes 16" long tapering to the pans. I only have about 1/4" below the flue pan and the rest of the heat is forced thru the flues. This worked well.

[RickinFarmington]

Thanks for the very informative response. That explains all aspects of the question. Will be cutting steel this week.

Rick

[RileySugarbush]

On my homemade 2x6 I have a straight back wall that comes up to just below my flue bottom level, leaving 1/2" below the drop flues. I don't have any problem with excessive splashing and don't lose any sweet in the condensate trough.

One difference is that my syrup pan is over long for a 2x6 at 33 inches ( a half pint pan) so the wall deflects the intense heat to the back of the syrup pan instead of the front of the sap pan. Strangely, this doesn't cause a problem with either pan and if I go nuts with firing and air over and under wide open I can even approach a steady 55gph, though it burns wood like crazy if I do that. If I fire and run blowers more reasonably I can run at 40 to 45 without excessive wood consumption.

I plan on reporting my first years experience with air over fire in the AOF thread shortly. It was interesting and everyone that ran it this year liked it a lot.