Base stack-how hot is too hot?

[ebliese]

I've got a question about base stack temperatures. I tried to do some research here but most people are talking about stack temperature in general. My questions are a bit more specific. This might be a dumb question, but I'm learning here. How hot is too hot for the base stack? If it starts to get cherry red? I've noticed my base stack can get a cherry red color so then I adjust the draft door to compensate. Our stack is 12 feet tall. I only have the draft door open fully when I am starting up the boil. I do not have a way to monitor stack temperature (other than eyesight). Just trying to get the hang of running this rig in a safe, efficient way. We had our third boil last night and it came with some excitement! Almost burnt the draw-off channel. Had to flood the pan. Our main mistake was starting with too low a level in the pan to begin with.

[ir3333]

Depends on how efficient your arch is. It should transfer most of it's heat to your fluid before it gets to the flue.
A cherry red stack may be over 900 degrees.I think a good boil with a stack temperature of 600- 700 would
be very efficient and save a lot of wood!

[buckeye gold]

your drawing too much heat away from your pan, I believe. Maybe shorten your stack and reduce the draw .

[johnallin]

A 2x4 rig shouldn't need much more than 8' of stack. Buy a stack thermometer from a local stove shop or hardware store, about $30 max and try to keep temps in the 5-800° range you should be good.
That stainless stack will eventually turn purple from the heat, no harm in it, it's just what happens.
Have fun with that new rig

[ebliese]

To answer some questions:

Our arch is an air-tight one from Smoky Lake.

I re-examined our stack and it turns out I could shorten it by taking a 2' section off and still be in accord with the 3-2-10 rule. So now the stack is 10' tall. I can't go lower than that unless I were to cut a section of pipe in half. Shortening the stack did seem to help the problem some. We still, on occasion, got to a dull red color on part of the base stack. I was running the arch with the draft door mostly closed. I was not running on a timed firebox reload but mostly going by the look (looking through the sight glass on our arch).

A stack thermometer sounds like a good idea. I'll take a look around for one.

[woodguyrob]

There's a great video from Smoky Lake running the Corsair illustrating it's GPH potential. It was done inside the show room so presumably a tall stack. It never appeared that they had a blazing hot stock base. If you call / email Jimi, Jim or Matt at smoky lake they can advise.
SmokyLake Corsair video https://youtu.be/HQPYXBiGheM

[berkshires]

What is the 3 2 10 rule? I have a new 2 x 3 evaporator, with 6' of 6" flue pipe (not counting a horizontal section to clear the shack.) Does that fit the rule or do I need to add more?

GO

[tcross]

i'm not sure of what the rule is, but i've always been told to have the stack at least twice the length of your arch. mine is about 3' taller than my arch due to getting it above the roof line... works great.

[n8hutch]

3-2-10 rule is your stack height to combustibles,as in when it comes up through your roof.

[berkshires]

3-2-10 rule is your stack height to combustibles,as in when it comes up through your roof.

Got it, thanks!

GO

[Aa2tn]

Also, it may help to put a stack of fire bricks to block the center in the back of your fire box right where the flue pipe comes in. That might slow down the hot gasses making them go around the bricks to the sides and up the stack. Similar to a layer of brick across the bottom of the back section of the arch to push gasses up into the flues of a raised flue pan....

[BCPP]

Also, it may help to put a stack of fire bricks to block the center in the back of your fire box right where the flue pipe comes in. That might slow down the hot gasses making them go around the bricks to the sides and up the stack. Similar to a layer of brick across the bottom of the back section of the arch to push gasses up into the flues of a raised flue pan....
Our firebox rises up about half way down the evaporating pan until it is about 1/2" from the bottom of the pan so all the hot gases have to pass through the raised flues.
I keep draft as wide open as possible as I want the fire (and thus evaporation rate) to be as high as possible. I shut draft down only to keep pan from foaming over. Typically draft is open around 25- 50%

[Sugarmaker]

I would say that it is too hot! maybe firing to often? Pushing wood back to much? several things can be factors. type of material your burning?
Keep boiling!
Regards,
Chris

[Balrog006]

3-2-10 rule is your stack height to combustibles,as in when it comes up through your roof.

Maybe it’s because I haven’t had any coffee yet today but I’m still not understanding this formula/ratio as described. Can you give an example of some dimensions and how it applies? Thanks.

[n8hutch]

I believe its 3 feet above the ridge , or 2 feet above roof line and 10' latteraly to any combustibles. Thats if my memory serves me correctly. It was just kind of a general safe chimney rule.

[Balrog006]

I believe its 3 feet above the ridge , or 2 feet above roof line and 10' latteraly to any combustibles. Thats if my memory serves me correctly. It was just kind of a general safe chimney rule.

So it wouldn’t have any application on a stand alone evaporator outside of a sugar shack then? I just have a 55gal drum evap on a pallet.

[buckeye gold]

found this https://www.bing.com/search?FORM=U528DF&PC=U528&q=3-2-10+chimney+rule

It is widely known that masonry chimneys are required to meet the 3-2-10 rule. This rule means that they must extend 3 feet above the roof penetration on the shortest side, and the top of the chimney must be 2 feet higher than any portion of the building structure within 10 feet.

[Michael Greer]

So I'm not an engineer or anything, but I think a red stack is just wasted heat. Heating the liquid is what we're after here, and it seems to me that there should more heat transferred to the liquid before it gets to the stack. Maybe the pans should have been longer?? with more pan exposed to the fire. Another thought is that combustion that should be happening in the FIRE box is actually happening further along. Flames in the stack aren't doing any work for you.

[buckeye gold]

I checked my stack temp the other day and it was 460 degrees two feet up the stack.

[ecolbeck]

I checked my stack temp the other day and it was 460 degrees two feet up the stack.

It would be expected that your stack temp would be lower than the OPs because you have AOF, correct?

I have no blower and my stack temps are around 900 degrees.

[maple flats]

On a smaller evaporator you will often have higher stack temperatures. Even on my 3x8 before I added AOF at time, but rarely I hit 1100-1200F. My thermometer is about 4' up in the stack. Now with AOF I usually run in the 600-850F range. The difference is because with AOF (air over fire) you burn more of the gases under the pans. While AOF may not be a good option for an evaporator under 2x6, maybe a blower under the grates may help burn more of the gases closer to the front of the evaporator. (If you weren't aware, wood does not burn, what burns is the gases that come out of the wood because of the heat. To see it up close, light a wooden match and look closely, the flame starts a distance above the match).

[ebliese]

Well, I added a stack thermometer (dial probe type) just a little higher than where the base stack joins the circular pipe. I found I was usually between 1100* and 1200* F. I was also timing my reloads today, every ten minutes. That seemed about right as the firebox would be about half full when I opened the door to reload. I did notice when I was getting into the 1300* F temps the stack would start to change to the reddish color (not the whole thing, mind you). Then after three or four hours of boiling my stack temp seemed to hang around 1300* F and I didn't get the reddish color. I also talked to two people at Smoky Lake at separate times and they said basically the same thing, it's normal for the base stack to glow at times because of the high heat. One of the reps at Smoky Lake said a 2x4 is a hotter unit to run because the heat doesn't have very far to travel before it goes up the stack (especially with a flat pan). I ran across another thread which they were talking about the StarCat and Dauntless from Smoky Lake and said the draft is real strong in these. So I'll experiment a little bit more and see what I come up with. Just for reference, I have a single wall pipe and burn a mix of hardwoods (ash, cherry, maple, black locust, a little tulip at times) split to wrist thick.

[buckeye gold]

It would be expected that your stack temp would be lower than the OPs because you have AOF, correct?

I have no blower and my stack temps are around 900 degrees.

You are correct. AOF lowers it

[ronnie 1]

22194If your stack is that hot, your loosing heat up the stack. if you can make this damper on your evaporator and install your stack on it you'll keep a lot of the heat under your pan where it needs to be. you can open and close it as needed depending on your draft in your stack on windy days. you'll cut down on your wood consumption by a lot also, just make sure that you have about 1/4" of space around your plate to allow for expansion so that it doesn't jam up. you'll have to play with it a bit to find the sweet spot and you'll notice that your boiling pattern will be better and your stack a lot cooler. we had this on our evaporator for a few years and it's made a big difference. Hope this helps. We got the idea from guys doing this in Quebec.

[Super Sapper]

Putting a damper in reduces your draft which reduces the oxygen to the fire. This reduces combustion which reduces your evaporation rate so longer boils. I would use larger pieces of wood or close off the inlet air vent more.