what to look for when buying small-scale secondhand evaporator?

[SapTsunami]

wow those raised flue / drop flue pans are pricey! Had no idea the upgrade curve was that steep

Will be focusing my search on a flat bottom divided pan

[maple flats]

For sure. A flue pan either raised or drop flue takes far more metal and time to build. I don't know if you are too late for 2025 season, but one of the best prices will be found at A&A Metal shop. His pans are all lead free soldered. 540-326-1407. He's Amish, his phone is in a small shed about 100' down his driveway from his shop. You will need to leave a message and he will call back. I just bought a 2x6 evaporator from him for $3100 earlier this year, raised flue. Drop flue was the same price. He told me he prefers building raised flue. It likely won't help but you can tell him Dave Klish sent you (but it won't hurt either). He is in Monterrey, Virginia, almost in West VA.

[BAP]

Check out Randy Worthern in Spofford, NH. He builds flat pan evaporators. He advertises them on Facebook Marketplace. His number is 6zero3-7four8-99two7. Currently he has 2x6 all flat pan advertised for $2000. They probably aren’t they same quality as some of the big name brands, but if they get the job done and get you what you need then that’s all that matters.
https://www.facebook.com/share/ASu5S...ibextid=79PoIi

[On the ledge]

Also check out W.F. Mason in Maine. He makes very nice evaporators.

[maple flats]

My original 2x was a drop flue. While 25-27 was not the average, I did get it at times, whyen everything was right. My 3x8 was a raised flue.
As far as how much detter for raised or drop flue over a flat pan, it all depends on the amount of added surface area over that in a flat pan. I forget the number but a flat pan has a given max boil rate based on its surface area. Once the flues are added, th surface area is increased several times. For example, on my final raised flue pan on my 3x8 had flues that were 10" tall and in the 3x5 flues pan the raised flues were all of the 5' less about 2" on each end and flues repeated fully across except another 2" flat all of the width of the pan. Those flues were 5/8" apart and maybe 7/8" wide, maybe less. When the added surface area is totaled that's how much extra surface there is to transfer the heat from under to in the pan. I can't give a number but it is several times better. In an evaporator that is 3x8 with a 3x3 syrup pan (flat bottom) and a 3x5 flue pan over well 75-80% of the evaporation occures in the flue pan, maybe over 90%. Iv'e read the comparison someplace but I don't recall the numbers.
Just remember that it increases the surface area many times.
If I remember to check it in my new evaporator, another 2x6 I'll get a count, and try to do the math based on the measurements. Maybe someone on here will chime in.