Looking for Firebox help

[nhdog]

Several years ago, I took part of my woodshed and turned it into a 10'x15' sugarhouse. I used 2 modified wood stoves and finished the syrup on a propane burner.

I now have a 220 gal tank (60"x24") and have finished welding it up to hold 3 full size steam pans.

My plan for the firebox is 20" deep, 17" wide, 16" from the grates to the bottom of the first two pans. The flue will be about 2.5" deep under the 3rd pan and runs to the 6"x12' stack, which is about a foot beyond the 3rd pan. I'm thinking this will work for the firebox.

Any comments or suggestions before I weld up the frame and do the brickwork?
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[hookhill]

How about sloping the back of the firebox so that the flames can shoot up to that last pan.

[barnbc76]

Do you have covers to put in place where the pans go fir when you start consolidating near the end? I would parobably make the fire box as large as you can, I think mine is like 24" deep. Also if you can get a fan it makes a lot of difference in evaporation rate. If possible consider building it in a way so you can expand, maybe a 2x3 pan. Others would probably suggest a ceramic blanket insulation or fireproof foam board. Where did you find the glass for your door?

[johnallin]

Any comments or suggestions before I weld up the frame and do the brickwork?
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It looks pretty darn close to the wall in the back there...you will need some protection on that wall if you don't move the rig out further.

[buckeye gold]

I agree with the others suggestions. The two things I think you should address is how close that thing is to an OSB wall. I would line that firebox with ceramic blanket and then brick over it. I also wonder if the pans should not be farther back. I will wager that first pan won't boil very well, draft naturally wants to pull your heat backwards towards the flue. You have room to set them back.

[nhdog]

Thanks for all your inputs.
First of all, I have a metal heat shield running up behind the arch and stack. I took it down temporarily while putting the stack up.
Yup, I have 3 covers to cover the openings when i remove the pans.
I got the glass from an old wood stove. Then I made a door to fit it and the arch.
I plan to insulate the box and add AUF through the draft/ash cleanout door under the grates.
Yeah, I agree that front pan probably won't boil too well as it is now.
A couple more questions:
Is it more effective to extend the firebox partially under the third pan, or is it better to force the flue path up a few inches beneath the pan bottom?
Would putting a damper in the stack help keep some of the heat in? Or would the restriction reduce the firebox burn?
Thanks for all your help

[johnallin]

May also want to clean up the straw around the rig...big fire hazard with coals dropping out of firebox ;)

[maple flats]

Most likely you only want 1.5" under the rear pan not 2.5". You want to push the heat up to the pan. One way to calculate it is measure the stack area, then divide that by the width of the arch, the answer is about how much space you want under the 3rd pan.

[Sunnyacres]

I'm confused my base stack is 6x22 and my arch is 24" wide that would mean I need 5.5 under my rear pan. That doesn't make sense to me could you please explain. I don't think I would want that much space under my pan.

[berkshires]

I'm confused my base stack is 6x22 and my arch is 24" wide that would mean I need 5.5 under my rear pan. That doesn't make sense to me could you please explain. I don't think I would want that much space under my pan.

The area of your 6" stack is pi x (radius squared).
R = 3"
R squared = 9"
9 x pi = 28"

So if your arch is 24" wide and you want to calculate how many inches you want between brick an pan to equal 28 inches, you divide 28 by 24, to get about 1.2"

That make sense to you?

GO

[Sunnyacres]

Yes that makes sense but my stack is not 6”. My stack is a 6x22 rectangle at the base.

[berkshires]

Yes that makes sense but my stack is not 6”. My stack is a 6x22 rectangle at the base.

You say "at the base". Is the whole thing 6x22? If so, then I hope you have a monster firebox LOL. But I assume you mean that's just the connector, and most of the stack has an internal open area much smaller than that. Right?

[n8hutch]

Yes that makes sense but my stack is not 6”. My stack is a 6x22 rectangle at the base.

Your base is a over sized rectangle like that because it's a transition/change in direction of flow, your flue gases are changing direction from a horizontal path of Gravel to a vertical path, if it was only 28 cubic inches as your 6" pipe would be it would be much too restrictive to promote a good natural draft because the gases would be trying to go through a sharp corner if you will, with a 6" opening the gases travel in a arched curve rather than a square turn up. Does that make sense?

I would go with a 1" gap between the pans and your arch rail, then when you add your gasket material you should be somewhere between an inch and an inch and a half.

[Sunnyacres]

You say "at the base". Is the whole thing 6x22? If so, then I hope you have a monster firebox LOL. But I assume you mean that's just the connector, and most of the stack has an internal open area much smaller than that. Right?

The stack base is 6x22 tapering up four feet to an 8" pipe coming out the back. I had to come out the back because I could not go thru the roof since it's there's another level above our shack.

[berkshires]

The stack base is 6x22 tapering up four feet to an 8" pipe coming out the back. I had to come out the back because I could not go thru the roof since it's there's another level above our shack.

Okay, so if the inside diameter of the pipe (less than outside if it's double-wall) at its narrowest is 8 inches, that's what you want to use to calculate the size of your stack. If it really is 6 inches inside then you want an inch and a quarter between pan and bricks. If it's 8", here are the new calculations:

The area of your 8" stack is pi x (radius squared).
R = 4"
R squared = 16"
16 x pi = 50"

So if your arch is 24" wide and you want to calculate how many inches you want between brick and pan to equal 50 square inches, you divide 50 inches wide by 24 inches, to get about 2 inches high.

Cheers!

[Sunnyacres]

Ok I'll try 2" my first year we had like 6" and each year I shrink it down and inch but still think I have too much space. I built by evaporater with a deep ramp since we are adding a flue pan this year. (Hopefully if time permits). Thanks for the help.

[Super Sapper]

If you are going with a flue pan you will want no more than a half inch under the bottom of the flues to force the heat up into them.