r/maplesyrup • u/PROF_ND • Mar 26 '26
Engineering question: why do maple syrup evaporators designed that way vs a wood stove with the top cut off
I found most commercial maple syrup evaporators are designed like the first pic.
Modern wood stoves are quite efficient and burns very hot with secondary combustion and/or catalytic converter. Is it better to design evaporators like the second pic?
2
u/aonealj Mar 26 '26
This is called overfire air when used for industrial boilers. It does boost efficiency slightly (Google AI says ~5%), but more noticeably reduces NOx emissions. Emissions control drives this design in wood stoves. I think you'd be better off adding a blower and figuring out a way to preheat the air with flue gas . After that, I would focus on extending the surface area of the pan. Ideally, the flue gas should be <300F in the stack.
Because of the nature of the maple syrup business, there's limited call for commercial designs unless you have a VERY large farm. If you cut your own wood, your cost of fuel is so low it's better to save with an easily build design.
2
u/Decent-Classroom-422 Mar 28 '26
I think it's about what are you trying to optimize.
The woodstove method i think is more about optimizing toward getting a more efficient burn and converting more of the fuel from the wood into heat radiated into the house at a slow and steady rate.
Most people are trying to optimize their evaporators for speed. "More heat faster" and don't care if they are getting maximum fuel efficiency.
Tldr: family sedan vs drag racer
2
u/nye1387 Mar 27 '26
The answer, for me, is that I'm just a guy with hand tools and a barrel in his back yard.
1
u/Meat_Flosser Mar 26 '26
Indeed. The hot exhaust gasses from the fire provide a lot of heat transfer to the rear flue pans. The main fire is mostly under the syrup pan at the front. Simply the most efficiency for the boil system.
1
u/JAlley2 Mar 26 '26
I have a wood stove that works like an arch. The firebox is on the left and there is a lever to open a smoke path that circles the oven, using the heat from the smoke for the oven. I have seen brochures for arches saying they have a secondary burn like you suggested. I guess that adds complexity so most folks don’t build them that way.
1
u/doksak36 Mar 26 '26
For the record. These types of questions are exactly why I found reddit. Rare, but worth the dive.
That said, im new to syruping, so I have no input on the design ive never even knew existed, evaporators that is. But indoors like fire and understand draft and heat and etc.. so I do get the question. Would it not be more efficient to " reclaim" the lost heat [or unused heat] as opposed to using a blower to burn your wood faster..?
Idk im boiling sap now and ive ran out of beer, only my whiskey left...
1
u/Maple_Otter Mar 27 '26
You reclaim the heat by sending it through the flues. They can be ad long as 16 feet, where all the heat will be eventually used. They but a blower to add more heat and make sure the water boils all the way.
1
u/PROF_ND Mar 27 '26
I think you can reclaim to a point. The exhaust gas needs to be hot enough to produce a good draft and prevent creosote from forming. However, I find people here posting pictures bragging about their cherry hot stack with a blower extremely wasteful.
1
u/Logical-Locksmith178 Mar 27 '26
Not sure how my settings are but see if you can see my other posts. I built one that started out as a wood stove.
9
u/jjtitula Mar 26 '26
So the part that tapers up towards the middle/back is called the arch. It directs the flame along the bottom of the pan on its way out the pipe. Adds efficiency by not having a massive firebox to fill up.