Rectangular flue stack question

[Hunt4sap]

I'm wondering what the best size as far as a width and depth would be for creating my exhaust flue area on my oil tank evaporator I'm building now?
I put a 6-inch ledge 4 a preheater pan 9 in above the other level I'll include a picture to show what I'm talking about, so I'm wanting to put a rectangular exhaust out of the top of my oil tank so that the flame get spread out along more of the pan to create a more efficient boil as I've seen this in commercially made evaporators ( wondering what's best size to create this opening in top of my oil tank?)
I can go as wide as 24 in which is the width of My preheater Pan and as deep front to back on the evaporator length of the oil tank 3 in...
Thanks Matt18731

[Haynes Forest Products]

Matt In my humble opinion is your going to get a lot of heat to the pans without any help from the exhaust/flue stack area. I like the transition from the firebox to the back of the arch. I think you might consider the design a 2 part pan set up because your warming pan is going to have direct flame contact. You might be surprised to find the sap simmering or even boiling.

My assumption is your plan is to come out the top of the rounded "archway" with the flue stack and I believe at that point it won't have much effect on the pans below as long as you use a size that isn't restrictive. You don't want it to small BUT to big and your draft will suck all the heat out also so. You can always restrict your stack but you cant force a NATURAL draft. Nice looking configuration good luck and keep us in the loop.

[Hunt4sap]

18732
Picture of tank part I have left from creating opening...
It's sitting on top where I plan on cutting it into exhaust opening.this leftover part needs cut down to size still I just set it on top to show approximately how/ where I plan on putting opening in evaporator top to get fire to lick bottom of preheater pan...

[Haynes Forest Products]

You just boggled my mind I don't see what that is. :confused:

[Hunt4sap]

Let me show a picture of what evaporator top looks like without leftover part sitting on top...18733
See if comparing picture s helps at all, I guess it's easier for me to visualize it because I know what I'm trying to build I just am unsure of how big to cut the opening in the top of the oil tank evaporator to do a good job?

[Hunt4sap]

Here's a different view18734

[Hunt4sap]

I'm going to show a outline with duct tape in next picture, give me a few...

[Hunt4sap]

Here's what I'm getting at...
Shown on inside duct tape line shows 2" wide exhaust flue opening proposed area on top edge of oil tank evaporator...
18735
Im leaning more towards a rectangle opening that measures 12" long by 2" wide which will be cut out/welded into top of oil tank that I could then attach a stove boot that would measure 12"by 2" and taper up to my 6" stove pipe( I have excellent draft due to 14' of stack height that vents through my roof)
I just wondered what experience anyone has with doing this type of stack to mimic what I've seen in commercially made evaporators to spread out the flames from fire box some ,compared to just a 6" round flue opening...

[Hunt4sap]

Here's another view...18736
The ledge area 9" up from 27"by48" evaporator pan area is where I'll have a 24"by 6" by 8" deep preheater ( built above so I can utilize a ball valve to open to add preheated sap from warmer into large evaporator pan...

[Haynes Forest Products]

I know this sounds silly but your not spreading the flame/hot gasses out. Your forcing them back into a smaller area if you go with a smaller stack. I think its a good plan. Its more work but hey that's what we do.

[Hunt4sap]

In my mind I wanted a preheater so I don't have to run a turkey fryer to preheat and I've seen commercially made evaporators with a similar setup so I'm trying to utilize my specific setup to maximize my efforts...

[maple flats]

Looks good except the preheater may get too hot (and boil super hard in the preheater pan), if it does, weld a top on that part.
What is the size of the arched portion where you propose putting a 2" wide by long rectangular stack? If it is at least 4-5" front to back, just take an 8" stack and make it oval on the lower end, then reduce it to 6 if you want, but I think you would do better if you have an 8" stack. If you reduce it to 6" it will be easy to change to 8" later. A firebox 28" wide will want more than a 6" stack to get maximum performance. If you are going with natural draft, make an adjustable air inlet at least 5" x 10" and when you get boiling adjust for best performance. The shape of that back rounded portion will draw well from the whole width, you do not need the stack to also spread that wide.

[Hunt4sap]

I have a piece of steel (6"by 24")for preheater area if it gets too hot

[Haynes Forest Products]

If it runs to hot run it deep, if the back gets that hot then the front should be ripping.

[Hunt4sap]

I hear ya,
Everything I've done so far with maple syrup has been a trial by mistake
Hoped by asking this original question that someone has done what I'm about to do and I could learn from there experience before I cut my tank.
My original reason for making it 12 inch by 2 inch rectangular is so that I could just text Gru a stove pipe boot that is already pre-made on to my original reason for making it 12 inch by 2 in rectangular is so that I could just screw a stove pipe boot that is already pre made on to what I fabric a onto my oil tank evaporator

Secondly because stove pipe is very thin gauge metal in my oil tank is pretty thick gauge steel and my transition point is easiest done by me welding what I already have into tank and then buying a 12 inch by 2 inch Buy 6in Round stove pipe that I already have ran 14 feet up through the roof...

[Hunt4sap]

That's pretty difficult to follow but talk-to-text will do that...

[Haynes Forest Products]

Having 14 ft of pipe will give you some real nice natural draft. I say hit PRINT.

[Hunt4sap]

Yes it does draft awesome(14') stack pipe
Used last 2 years to evaporate with my 55 gallon barrel stove evaporator, so this is my upgrade to that original I started with that's in my avatar picture...
Thanks for your guys thoughts on this ( but I'm not sure it has helped me make a decision on size of exhaust to cut in top of oil tank)

[Super Sapper]

The 12 x 2 opening is too small. That is less area than a 6 inch round stack. I would go with a large enough opening to equal an 8 inch stack even if you stick with 6 inch. You may have to add onto the back for this.

[maple flats]

You referenced wanting to get ready made components and said you wanted to use a 2x12 and a 2x12 to 6" round, both of those will only be 28 ga sheet metal, do not use them for your stack. It would likely burn thru in less than 1 season. Those pipes, stack and fittings are made for forced air heat, not for a class A chimney or even one for a gas vent. For your stack you must use at a minimum 24 ga and if you buy stack from a maple manufacturer galv. stack will be either 20 or 22 ga. If you buy locally go to a sheet metal shop and have it made in 22 ga. If you go with SS it can be 24 ga but while SS will last far longer, it will cost big bucks. A 22 ga. galvanized stack will last 6-8 years, especially if you keep it dry in the off season. If you don't have a cap to put on or close, just use a bucket or if it will fit, use a #10 can after the season to keep rain out (I think if you have a 6" stack a #10 can may slide over it). Even a plastic pail will hold up to UV enough to last 1 year, some may not last 2.

[Hunt4sap]

Thanks guys, last 2 posts are helpful
I will re- think that area before cutting it out now( the area that I have available is not quite enough for a 6in round to fit in the top)
This is why I'm trying to figure out what size rectangle to use because with the preheater ledge I ran out of space for the 6"stack, I could possibly come out the back and be much easier but I wasn't sure how that would draft or if it would work as good as coming out of the top?

[Hunt4sap]

The last two years I also had trouble with my 55 gallon barrel evaporator being vented out of the back and the stove pipe elbow actually broke loose in mid boil so that's why I'm trying to avoid coming out of the back on this build...

[Haynes Forest Products]

Hunt4 doing the math with your template of 2X12 is under the 6" stack square inches. as Super sapper said So increase it to 2-1/2 X 14" and your OK so maybe go to 18 X 3" and go with 8" stack and you will be fine. Stay away from the back the rig will look and perform better. out the top. Plus get some angle iron around the warming pan/mini pan opening.

[Hunt4sap]

Ok thanks fellas
Yep, I need to weld angle iron on preheater area
Cross support for evaporator pan
Cut opening in top for flue
Weld bolts to inside to attach 1" ceramic blanket
Brick inside
Get pans from WF that he's making for me
Cut stove door in
Get blower
Drill 2" emt that will provide AUF
Buy a 22 gauge rectangle to round boot
And finally extend my sugar shack 6' out to make more room for bigger rig!!!
It's alot but I've make good progress on new unit so far and I'm glad I asked about rectangular boot size for proper draft

[Haynes Forest Products]

Dang it Matt you remind me of the guy in front of me at the auto parts store.

Counter guy, Can I help you?
customer, My car won't start!
Counter guy, what do you need?
C Don't know!
CG, whats it doing?
C Nothing!
CG Does the engine turn over?
C No!
CG Is the battery dead?
C I don't think so!
CG what does it do when you try and turn it over?
C I don't know!
CG What do you mean you don't know what happens when you turn the key!
C I don't have the key because it's broken!

Now matt I'm just funning with ya. But after all the discussion you mentioned a blower and AUF

[Hunt4sap]

I've been asking so many questions in different threads on here I lost track and thought I had mentioned those 2 things in this thread earlier, so woops!
Does those 2 things being known now change the thoughts on rectangular opening size?

[Hunt4sap]

18746
3.5"x 18" fue opening drawn out, there's no turning back now!
It equals 63 square inches( as close as I can get it to 8"x8" round pipe... Look right fellas?

[Haynes Forest Products]

Now before we all second the motion to allow you to continue with the build I have one request. Before you cut the opening get the angle iron sculpted to the round area. Looking god.

[Hunt4sap]

18751
Not sure about sculpting angle iron, but here is start of my exhaust stack I worked on a bit today...

[Hunt4sap]

18752
A different view as I welded it together...

[maple flats]

That will work. You will want to attach the stack to the extension you are welding up using screws or steel pop rivets.

[Hunt4sap]

Here's what I've come up with( top will get cut out to a oval x 8" stack when I get one...)
18753
18754
Hopefully tomorrow I'll get this thing wrapped up as far as I can go for now till I get stack components

Need to move wall in SS 6' and add center floor drain, add gravel, compact, maybe concrete if I get to it before I go elk muzzleloader hunting in Colorado...

[Hunt4sap]

Hey maple flats,
Why not weld my oval stack piece into flat top area?

[maple flats]

You could weld it, but when it needs changing you would then need to deal with that then.

[Hunt4sap]

Gotcha, I'm still thinking over my best way to connect it so I appreciate the options

[mol1jb]

As thin as smoke pipe metal is even if you welded it on it would only take you a few minutes to cut it off and change it. And on a oil tank arch it should last you around 4 year or more depending on how hot you run it.

[Hunt4sap]

Ok, I had to get some .024 wire for my mig to be able to weld 24 gauge and I did get my floor leveled out and gravel added today, so I'm creating closer to a concrete floor( might still happen this year?)not a big deal if I don't but if I can get it concreted then I won't disturb gravel that's already been leveled/ compacted...

[maple flats]

Back when I had a wood floor because the $ were not there, I poured the floor with the fully bricked evaporator in the sugar house. I just made a hoist and raised the rig high enough to pour under it. At the time I had a 3x8, I still use the same arch but with new pans.
For that I got 2 long pipes (each 3/4" x10') and I placed them on top of the bottom cord (the ceiling joists, of the trusses) parallel to the side of the arch and on one end of each I put a T with about 30" long handles to turn the pipes. I then used electrical clamps 1 size too big to anchor the pipes from walking as I cranked the pipes. I then took some cable, attached it to one of the pipes, slung it under the arch and back up to the second pipe. On the end of each turn handle I put a pipe cap. I only had 2 such cables because I thought it too hard to get 3 to share the load equally. Then I started the crank one side but just before it got tight for lifting, I used a roughly 3' board the hold that arm of the crank from unwinding by placing it on top of the joists between the one each side of the crank arm, with that arm pressing on the board. Then I moved to the other side and this time I cranked until the evaporator lifted 3-4" on that side, and I then blocked that from unwinding. I then worked back and forth, raising each side about maybe 6" at a time. When I had it lifted to within a foot of the open ceilings joists I quit lifting. I then screwed a 2x4 vertically to a ceiling joist about 1.5-2' in from each end of the arch. Once I had 4, 1 at each vend and side, I screwed a 2x6 across under the arch, tight to the underside of the arch to hold it more securely. I then backed off on the cables slightly so both the cables and the safeties shared the load. Then I cut off the excess tails on the vertical 2x4's at about 5-6" below where the 2x6 attached, so I could walk under to work. I then removed the wooden floor, hauled in lots of crusher run, packed it using a plate packer. Then I got the concrete poured, mixing my own (I have a tractor mount mixer that does a decent load at a time. About 2 weeks after pouring the concrete, I re-tightened the cables, removed the safeties and lowered the arch onto the finished floor. That worked quite well for me. I did it that way because I didn't feel I could move the rig from the building without damaging it somehow.

[Hunt4sap]

Made more progress on my OTE today.
18781( oval stack cut into rectangular stove flue.
18782AUF feeder tube drilled and end welded on/ cut to final length( first holes 8" from door)
18783door bolted on( bought used and plan on insulating it and wrapping round stove rope around inside of door to create "airtight" as I'm going to get for this year...
18784bolts welded inside for attaching 1"fireblanket
Need to get a fan/ gate for attaching to 2" feeder tube pipe from rear of stove ...
Getting evaporator pan/ preheater pans made from WF Mason and can't wait to do a test boil with some H2O!!!

[Hunt4sap]

1890018901
Finally got her ceramic blanket installed today!!!

[billschi]

I like it Hunt. It looks very similar to what I built except I have enough room for a buffet pan for preheating.
The ceramic blanket looks good. I'm curious about how you're good to get rid of the ash. Aren't you worried about it getting torn up when shoveling the ash out? Are you putting firebrick in the firebox?

[Hunt4sap]

I need to add my fire grate above my AUF pipe, and also fire brick burn chamber to protect it from bumps with wood...