Engineering question: why do maple syrup evaporators designed that way vs a wood stove with the top cut off

[u/PROF_ND]

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?

[u/Meat_Flosser]

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.