Back Baffle placement Raised Flue

[New Hope Mapleman]

I have finished extending my arch and am trying to finish the back baffle on the set-up. I have gotten a couple answers to my back baffle placement question and they differ. Here are the facts I know.
18" Stack=254.34si
12" From Back of pan to Baffle = 528si
24" From Back of pan to Baffle=1056si

There must be some type of formula that is to be used here, or are we all paying manufacturers to wing it?!

This is a 4x14 arch Forced Air Inferno.

We had problems last year, and I was told to shorten the gap to 12" It helped, but I don't want to kill the new pans and or have to rebuild the baffle later.
Thanks for your help.
Dan

[802maple]

In building the Intens- O- fire I match the base stack which I believe yours must be around 10" finished including the brick or insulation which ever you may use

[Fred Henderson]

i have no idea what you guys are referring to but I am very interested to learn.

[New Hope Mapleman]

802 Maple
So I should match the thickness of the base stack to the open area between the baffles and the end of the flues, not including the outside wrap of the pan?
I'm guessing this one issue makes a HUGE difference!
Thanks
Dan

[Maple Hill Sugarhouse]

post edited

[Fred Henderson]

Thanks for the explanation. You see my new outfit is a drop flue,but at the back right before the stack there is another flue that goes all the way across connecting all the flues as it goes. It serves as the flue drain and is piped and valved to the outside of the arch. When it was delivered(night time) the guy said to have a min of 1 1/2" between the flues and the bricks. He also said that it could be more, so I got about 2". I have boiled water for about an hour so in a few months its going to be interesting.

[New Hope Mapleman]

:oops: Thanks for explaining for me. Sorry Fred I didn't mean to ignore you.
I was going to mention that I got a picture from your friend on the tank, but no price. I e-mailed him, but that was two weeks ago.
Dan :)

[Fred Henderson]

He is really not a freind of mine . I got his name from Bill Mason of Mason Welding. I guess that Bill made the guy an evap about 10 years ago.

[WESTVIRGINIAMAPLER]

Fred,

2" seems like an awful lot for clearance. I have 1" or less between my firebrick and flues. The more clearance between the firebrick and flues, the less the heat and fire will be pushed up into the top of the flues. :?

[Fred Henderson]

Brandon, Your drop flue is not built like mine, your flues are total open at the back. I only have 2" at the back near the stack. The stack has to be able to pull draft from someplace. If I only have a 1" space for 5 feet then why do I need an 8"x12" base stack. I think I got it right but time will tell. I tryed it after I bricked it then I took the pans off and put zonolite in till it was 1" from the flues. It would not draw very well so once again I took the pans off and remove the zonolite and added 4 more feet of stack but never got to try it. I have finished the hood and preheater and I think I am ready.
I might have to get a professional to come a check it out.

[WESTVIRGINIAMAPLER]

Fred,

Sounds great and sounds like you have it right. I didn't realize your evap was built a little diferent! :D :wink:

[Fred Henderson]

Brandon, Thank you for your concerns. Its good to have people on these boards that are will to lookout for one and another.

[brookledge]

Fred
I would agree with Brandon that 2" between the flues and the arch is too much but I'm not sure what type your arch is. You want to force the fire and heat through the flues, the fire that travels under the flues in that 2" space is not coming in contact with the pan and is heat lost up the stack.
Maybe you could start the distance at 1" and as you get to the back lower it to 2".
Keith

[Fred Henderson]

Keith , Did you read this whole thread? That is just about what I did.

[brookledge]

Sorry Fred I missed that. Good luck with it.
Keith

[Fred Henderson]

Well don't miss any trees when you are out there tapping. :) :) :)

[JasonS]

Just trying to understand this whole raised flue thing. I'm converting from a drop flue (I called leader and they weren't much help). I have a new leader arch so I guess that I should run a row of bricks up in a straight line with the ramp. How close to the bottom of the pan should I come, even with the rails or just below? I understand the vermiculite idea but how thick should the ceramic blanket be? What density? After reading the threads up above I still don't understand the rear baffle. The arch is 2ft wide. How far does the rear baffle sit from the stack? Is it a gradual or sharp slope back down?
Any help is much appreciated.
Thanks,
Jason

[brookledge]

Jason
I had a drop flue style for years and then went to raised flue. I'm assuming that your arch has two sheet metal ramps. The idea with raised flue is that you need to force the fire and hot gasses up into the flues and then back down to go out the stack. The area in between the two ramps is dead space. Fill it with vemiculite and either brick the last bit or lay in arch board or fabric. You just need to keep the vrmiculite from blowing up the stack.
Any ways this area should be level with the top rails of your arch. With mine both the front and back are around a 45% angle.
Keith

[JasonS]

I don't have any sheet metal ramps, The arch was made for a drop flue. I was palnning on making the ramps out of brick?? How far from the stack should the back ramp start?
Thanks,
Jason

[brookledge]

Jason
I don't know if there is a standard or not. I will measure mine in a day or so if nobody else post the answer. Basicly you want to ramp it up as soon as possible while still keeping enough space for the fire to travel up into the flues and the same on the back only opposite
Keith

[maplehound]

The dealer told me that the first ramp should end about 1/3 of the way back ont the flue pan and then just the last foot or foot and a half would be ramped back to the stack. This is on my 3x8 rig.

[Pete33Vt]

The demenisions Maplehound gave are about the same as on my 40x12 rig. So if you go with that you should be pretty good as far as baffle placement.

Pete

[ibby458]

I haven't bricked mine yet, but I do have it planned out.

On my arch, the "choke point" is the stack base. (Choke point is the smallest area smoke passes thru in square inches) I added up the square inches of the space inside the firespace on the flues, and found that I needed to keep my brick 1" below the flue bottoms to equal the stack base size. On the front and rear, my ramps had to start and end 7" back from each end of the flue pan to maintain that space.

Since my arch was for a drop flue, I'm going bolt in angle iron in the desired clearances (allowing for blanket and/or bricks). cover it with stainless sheet and then blanket and brick it.

By careful consideration of brick sizes, I was able to arrange everything to maximize the use of full bricks, and minimize the cutting of bricks when I put it together. It'll use a few more bricks, but I won't have to cut many.

[New Hope Mapleman]

We finished our arch and test fired. Turned out great-boils all the way back!!~! The flues are 11 inch on my pan so don't just assume the placement is right for your pan. The front of the baffle is 15 inches from the front of the flue pan and the back of the baffle is 16 inches from the back of the pan. The center is filled in to the top of the rails. It's always nice when it works out right the first time.
Thanks for all the help with this guys.
Dan

[oneoldsap]

Your stack on a wood fired arch wants to be at least twice the length of the arch With no draft obstructions, I think 802 will agree with that