Yes, oliver 1, I think you understand.   My barns  and electric panels are about 500 feet apart and the cost to rewire certain circuits to another panel, while less than getting a larger generator is still a lot of expense.    I have no issue using a smaller generator  and running just the emergency loads of heat and ventilation because within and hour or three , I can have a larger PTO generator hooked up.  It's mainly the feed lines and secondary fans that I want to isolate and I think I could use a magnetic motor starter on those circuits to achieve what I want, but interested if there is another way or product to use.