I haven't measured mine out exactly, but the flat pan and the warming tank on my 2x4 seem to take about 12-15 gallons of sap. I like to keep the evaporator going for at least a couple hours once I bring it to a boil so 30-40 gallons of sap would be the minimum. Your 2x3 probably holds a few gallons less so 25-35 gallons might be a minimum for you. 150 gallons is probably about what it takes to sweeten the pan. I'd give Bill Mason a call, he has always been glad to answer my questions.