Previous to this season I was using ten wraps of 1/2 inch copper around the chimney pipe, that took 40F incoming sap to 160F. This year just for grins I doubled the wraps to see what would happen and I hit 178F. I have the tubing wrapped fairly tight so virtually no gaps to the chimney pipe but I think if I cover the tubing with some kind of insulation I could get it somewhat higher, I don't necessarily want to go much higher though. I also did some boiling without running any liquid through the preheater, my soldered coupling joining the two lengths of copper wraps remained intact, then ran sap through the preheater during later boils and didn't notice any issues. I like to experiment and try new things each season, to see what works and what doesn't. Also built a 3'x8' aluminum hood exhausted through ceiling (first year boiling inside the log sugar shack and was concerned with steam buildup), a few tweaks for next year but overall it worked pretty good.
2010 - 12 taps, turkey fryer, 4 quarts
2011 - 24 taps, homemade arch from old water tank, 16"x24" flat pan, 16+ quarts
2012 - 9 taps, 3 pints, what a season
2013 - 60 taps, homemade oil tank arch with 2'x4' flat pan, 16"x24" finishing pan on electric range, 55 quarts
2014 - 80 taps, homemade oil tank arch with 2'x4' flat pan, 16"x24" finishing pan on electric range, 40 quarts
2015 - 100 taps, 15 gallons
2016 - 115 taps, 13.5 gallons
2017 - 120 taps, 13 gallons
2018 - 130 taps, 11 gallons