I've been around Maple Production for over 60 years and have seen many 'creative evaporators', however coal was not a fuel of choice. Saw 3 new pellet evaporators this spring, and have worked with oil and propane since the late 50's. Biomass on a small scale, but coal just doesn't seem as 'authentic' as wood fired arches. Commercially no one would care, but mom, pop and the kids want to see the steam, roaring fire, and smell the wood smoke. By the way, the Sap House with pellet fire uses covered arches, steam is ducted to one exhaust, no residual heat, no cool smells.....too much like a Connecticut Landscape: tooooooooo perfect. No horse drawn wagon or scoot....you get the idea. Everything is all stainless steel.....nice, but no character. Like the fella says: It takes 'Rural Characters to MAKE Rural Character!'
Best of luck, because I would love to hear how it works out. After this dismal season, many will be headed off to other projects I think.