I don't know how big a generator you have or are planning on getting. I'm guessing your heat treating oven is somewhere between 3KW and 5KW. You might jot down the power ratings of all your equipment, including lights, heat, fans etc. THEN determine the maximum wattage you will ever need while working in your shop. With his information you can size your generator. With a little research you can figure out how much fuel you will need per hour. Then you can figure out whewther running a heat treating oven on a generator is going to be more expensive than having them sent out for heat treat.
Jim A.