What's with the slope?

[RileySugarbush]

I'm about to build an arch for some new pans- JasonS' half pint and 2x3 drop flue pans. I wonder why arches have a slope between the firebox and the flue. It seems to me that a vertical back wall to the firebox would maximize the length of the flue gases in close contact with the pans. The sharp corner shouldn't be a problem, there is one at the stack base already. It seems like a good thing to make the flue gases turbulent at the back end of the syrup pan My firebox is planned to be 19" wide (24" minus 2 bricks) x 20 deep x 18 high from grate to syrup pan. I plan on 1" space below the flues and I will have forced draft.

Any comments or suggestions?

[Pete33Vt]

From what I can guess is thats the way they made them when they first started, Not much forced draft back then. So they had to make them like that to get all they could for draft. I know there is alot of companies now that are making them with square fireboxes.

[mountainvan]

I layed some brick before the slope to make my firebox square. Added 10 gal/hr to boiling rate, I do have airtight forced draft, but I'm sure it would help any rig. Go with square.