My design of arch. Look ok?

[2wheelsadam]

Hope the pics show up. This the wood stove maple syrup arch I’m building. Biggest question I have is how much room do I leave between bottom of flat pan and the brick? Right now I’m thinking 3 inch. See schematics thanks

[whity]

I would leave an inch and a half between the brick and pan. Side brick you should have all the way to the bottom of the pan.

[raptorfan85]

For a flat pan I would do a ramp so make it wider at the firebox end and ramp it up to about 1 1/2" like whity said.

[2wheelsadam]

Why do you say ramp? I’m trying to understand this. I have seen some ramped and others not ramped. Why?

[whity]

Why do you say ramp? I’m trying to understand this. I have seen some ramped and others not ramped. Why?
The ramp creates a better draft. At the beginning of your ramp, "back of the fire box" have 3" to the pan and ramp it up to 1.5" at the back of the pan. Some keep it the same front to back as we do. But we have air over and air under to force the draft back.

[Super Sapper]

If you have a 6 inch stack and 24 inch wide arch leaving 1 1/2 inches under the pan would be good. You do not need any more area than your stack has. The reason for so little room is to get the heat on the pan and not have it short circuit farther under. I would get the heat up to the pan right away to take advantage of all the heat you can. When building it I would make it deeper under the pan and make up the difference with insulation.

[maple flats]

With a 2x6 finished size you should have a 7 or 8" stack, 8 is preferred. Then if you do it at 8" leave 2" at the rear. The ramp should be 12-16" front to rear in length and 3 or 4" in front and 2" in the back. Then the rest of the way back have 2". When you then put the pan(s) on use a woven gasket like this https://www.bascommaple.com/item/apgas25/gasket/ (available from most dealers and manufacturers for maple evaporators) which when compressed will give you about 1/8" or more space which then gives you the cross sectional area of an 8" stack. Then do not have a damper in the stack, you want it to fire as fast as possible.
The reason for the ramp is to gradually force the heat up to the pans.

[2wheelsadam]

I have an 8 inch pipe. Not sure how much difference that makes

[maple flats]

You need enough stack to effectively get the most evaporation from your pans. If the stack is undersized it will choke the fire. In fact, you show 27" width, I think you mean that to be the total width, not the width inside the firebrick that line the arch. If that is the finished width inside the bricks, you want a 9" stack. Also, For the back of the arch I see a step up before the stack starts. That should either be higher before the stack starts or should be a tapered rise. Look at all commercial designs, they use a long taper called a base stack, some only 3' long tapered, but most are 6' long. That is not just for looks, it helps the draft and spreads the heat better over the entire width of the pan. With a short arrangement like you show then into your stack the sides of the pan towards the back will not boil anywhere as hard as the center area.

[2wheelsadam]

18840

Do you see any problems with having back part. In schematic “A” was going to be used as a spot to put preheat pan on it with a valve. It’s higher then 2x4 frt pan so I could slowly add to frt pan when it was warmed up. The ramp from back of stove to where it goes down to 1.5 inches is 23 inch long then you have 2 more feet before it goes up the 8 inch chimney. I’m trying to use the top of old stove that I cut off that you see in pic. Maybe I have a bad idea or maybe there’s a better way?

[2wheelsadam]

So instead of a 8 inch round pipe would I be better off with 6x11 base stack? Or a 3.5x18 tapered stack? If I’m understanding this right you want a wide opening so smoke and heat travel under whole width of pan instead of traveling to the middle of a 8 inch pipe.

[raptorfan85]

Yes that's what you want. You want the draft to pull the entire width of the pan, so the wider base stack is much better than going right into the 8 inch pipe. Without a wide base stack all the draft will pull the heat and smoke to the middle and the back corners of your pan won't boil well. When I built my evap I ended up buying a commercial stainless base stack. It was money well spent.

[maple flats]

Yes, but go with a 20" or even a 22" wide x 4 or 5" then taper to the 8".
On my commercial made 3' wide arch it has a 33" wide base stack x 7" then it tapers in 6' length to a 12" round pipe. That gives you a draw over the entire width of the arch.

[2wheelsadam]

Thanks for all your great advise