Help me understand the importance of stack temps

[MapleME]

And before all you Wisenhiemers start saying "when you light a fire, the temp goes up"... LOL.

I see it mentioned a lot, and I just don't understand how its monitored, why etc. I mean, I understand you want a hot fire...but beyond that, Im ignorant on this topic.

So, do tell....whats it all about? Maybe it will be a post others who are newish will like to read too.

Happy new year from Brunswick, Maine....
Josh

[jmayerl]

Well I would say ideally you want as low a stack temp as possible. If its low(say like 600 degrees) then all of the availible heat from burning wood is being kept in the arch. Glowing red stacks and orange flames shooting out the top of the stack is wasted heat. Both of which I have! Lol. That is why if you can get the right mix of aof and auf to completely burn all the wood and gas you are doing great.

[Ausable]

Josh - If You don't plan on using Forced Air on your rig - you really don't have to be too concerned about it. However - with forced Air things can get mighty hot - kinda like a Black-Smiths forge. Don't want the stack to melt and things near the arch or stack to ignite from spontaneous combustion. So - when You use Forced Air temperature has to be carefully monitored and many things insulated.---Mike---

[MapleME]

Josh - If You don't plan on using Forced Air on your rig - you really don't have to be too concerned about it. However - with forced Air things can get mighty hot - kinda like a Black-Smiths forge. Don't want the stack to melt and things near the arch or stack to ignite from spontaneous combustion. So - when You use Forced Air temperature has to be carefully monitored and many things insulated.---Mike---

Mike, Thanks....Well I do plan on putting in my AUF blower from my old evap to my new Lapierre drop flue. Its nothing fancy, but it helped a great deal in my old hobby arch so I figured Id hold on to it and adapt it to this one...probably just slide it in under the grates and give it a little "oomph!"

So back to stack temp....

[Sugarmaker]

Even natural draft and the right wood can have extreme stack temps . Its really just another gauge in the system.
I know that if my indicator on the stack is pegged at 900+ F then its too hot and I need to dial the fire back a little. I agree that 600 is about right, but each arch is different and there are different types of thermometer for stacks ie, exterior and probes.
Regards,
Chris

[MapleME]

OK, im understanding more... So its just another way to monitor what you can't see.... I guess figuring out where the sweet spot is can be tricky, I assume...

[MilesTeg]

Now I'm going to go against the grain here I have a AUF 30X8 leader max pan setup. I personally like to see my stack temps as high as possible it's actually become a game to see who can get them higher on our rig. The thought behind this yes were are losing all of that heat, but think about how much more heat is hitting the bottom of the pans until it gets to the stack probe. Our probe is in the upper part of our base stack about 5.5 feet off of the ground. Our highest temp so far has been 960 F. We have taken precautions and have put fire blanket around any wood that is within 2 feet of our stack. Take it as is but I can tell you what when we push those high numbers we get rid of some sap in a hurry.

[wiam]

I guess I am with Milestag. My Condar Probe thermometer http://www.condar.com/probe_meters.html goes to 1700 degrees. I run my stack at about 1400 at eye level(arch is 10" off floor) Yes I probably "waste" wood but last 2 years I made over 400 gallons with less than 6 cord/year. This is with a blower from a mobile home furnace on a 2x6. I do not run a speed control, just a damper on one side of intake

[Brad W Wi]

I'm no expert but I also agree with MilesTeg and waim. I run a 2x8 Dallaire. My temp probe is 3' up the stack. I'll get temp reading 1100 - 1200 degrees using maple and ash wood, 3" to4" in dia. I know that when I'm firing it up It boils great. I too have stack wrapped and 2bys that are close covered with fire board also a metal roof. I have a stainless stack and no forced air although I'd like to go that route but I'd likie to talk to someone with the same size unit as I have.

[oneoldsap]

1200 Deg. without air ? I think you have a very optomistic thermometer there Brad .

[Brad W Wi]

Unless the therometer is off (which is always possible) I've read up to 1200 degrees.

[Ausable]

As long as We are on this subject. What is the longest Eveporator Pans You ever heard of on a Rig and did it use Induced draft along with the forced draft? Could you go like a 6 foot x 50 foot.......You would almost - for sure - have to have both forced and induced draft. I have heard that in Quebec the large Commercial Operations have some large Evaporators.....wonder if the use both tyoes of draft together? Forgive me - guess I'm thinking out loud...lol...

[wiam]

1200 Deg. without air ? I think you have a very optomistic thermometer there Brad .

It also depends on type of thermometer. I have been told probes will read higher than surface but are more accurate.

[Dave Y]

Unless you have a arch that is designed with no natural draft you should have a fairly hot stack. The hotter the stack the hotter the fire is under your pans.The faster it will boil.

[DrTimPerkins]

...What is the longest Eveporator Pans You ever heard of on a Rig ....

Largest standard commercially-produced rig made (that I know of) is 6' x 18'. Typically if people want something more capable, they'd either have a custom-made rig, or use two evaporators in series (with the first one often being only flue pans). There are some really interesting custom-made evaporators out there....often steam rigs, which allow a higher degree of customization since you don't have the same arch requirements/limitations. With recent improvements in RO, it is usually easier and cheaper to simply increase the RO capacity in some way rather than the evaporator capacity.

[MapleME]

Largest standard commercially-produced rig made (that I know of) is 6' x 18'. Typically if people want something more capable, they'd either have a custom-made rig, or use two evaporators in series (with the first one often being only flue pans). There are some really interesting custom-made evaporators out there....often steam rigs, which allow a higher degree of customization since you don't have the same arch requirements/limitations. With recent improvements in RO, it is usually easier and cheaper to simply increase the RO capacity in some way rather than the evaporator capacity.

Surely with the efficiencies in RO, and with the huge prices in steel, cant be cost effective to build bigger evaps these days i can imagine...

[Ausable]

Thanks Gentlemen - I Guess with R.O. and the cost of Steel it would be silly to go larger - No gain. ----Mike---

[RC Maple]

Back to the stack temperatures - this being my first year, a friend took me to look at a sugar shack of someone he knew last summer. This set up had a 2x6 and he showed me the temperature gauge on his stack and said he tried to keep it at 450. The magnetic temp gauge on my stove pipe shows the ideal temp range at 400 - 600 and it says "danger" above that. I just have a barrel evaporator and did my test boil last Saturday. We tried to keep the temperature under 600 while shooting for 450. What would be the big deal operating in the red? From the temperatures I see in the previous posts it is common to be at 1000+ degrees. I have 6" black stove pipe connected to double-walled stainless that goes up through the roof and for now use no auxillary air. How much attention should I pay to stack temperature? Thanks for the help.

[OldManMaple]

The thing to remember with Metalbestos or Duratech or ANY factory built chimney listed to UL103HT is that these are residential type chimneys with 1000 degree F maximum output under normal operating conditions. They're tested to 2100 degrees F as in the event of a chimney fire, which is normally short in duration. If you are going to use factory built chimneys and run it higher than 1000 degrees F, the chimney pipe should be installed with more than the minimum 2-inch clearance to combustibles to be on the safe side (and then use the warranty to light your first fire).

[MapleME]

The thing to remember with Metalbestos or Duratech or ANY factory built chimney listed to UL103HT is that these are residential type chimneys with 1000 degree F maximum output under normal operating conditions. They're tested to 2100 degrees F as in the event of a chimney fire, which is normally short in duration. If you are going to use factory built chimneys and run it higher than 1000 degrees F, the chimney pipe should be installed with more than the minimum 2-inch clearance to combustibles to be on the safe side (and then use the warranty to light your first fire).

Good advice OldMan

[oneoldsap]

Back to the stack temperatures - this being my first year, a friend took me to look at a sugar shack of someone he knew last summer. This set up had a 2x6 and he showed me the temperature gauge on his stack and said he tried to keep it at 450. The magnetic temp gauge on my stove pipe shows the ideal temp range at 400 - 600 and it says "danger" above that. I just have a barrel evaporator and did my test boil last Saturday. We tried to keep the temperature under 600 while shooting for 450. What would be the big deal operating in the red? From the temperatures I see in the previous posts it is common to be at 1000+ degrees. I have 6" black stove pipe connected to double-walled stainless that goes up through the roof and for now use no auxillary air. How much attention should I pay to stack temperature? Thanks for the help.

That magnetic thermometer you bud is using is for a wood stove , not an evaporator . Those are for making sure not to get too hot and crack flue tiles . You want your evaporator to be as hot as you can get it , that's when it's operating at peak efficiency (sp) . When your stack temp drops a couple hundred degrees , it's time to fire . When making Syrup , hotter is better ! The faster you get your sap through your evaporator the lighter the Syrup that you make !

[wiam]

That magnetic thermometer you bud is using is for a wood stove , not an evaporator . Those are for making sure not to get too hot and crack flue tiles . You want your evaporator to be as hot as you can get it , that's when it's operating at peak efficiency (sp) . When your stack temp drops a couple hundred degrees , it's time to fire . When making Syrup , hotter is better ! The faster you get your sap through your evaporator the lighter the Syrup that you make !

I agree with this, but I will also say do what YOU are comfortable with.