It seems that with the technology in the maple industry now has made a 2x6 evaporator very versatile. With flat pans we were boiling between 20 and 30 gph. We went to a Max Flue pan and are now able to process 40-50 gph. As we grow and add taps we can add equipment to up our processing capacity. We started at 250-300 taps and now have grown to 1060 on the same evaporator. 2x6 would be my short answer.