One of the biggest deciding factors is the cost of the oil compared to wood. Do you have a source of free wood and do you have the time to devote to harvesting it and getting it to the sugar house? If you have to buy the wood it is still more labor intensive than oil. You need to decide which way will work best for you. I have seen oil fired 2x4 evaporators and I have also seen 6x16 wood fired evaporators. The size of the evaporator isn't the deciding factor.