We use a 3,250 watt generator that I bought at B.J.'s for $200. Two days after we brought it home, our power went out for eight hours, so it paid for itself in just one use. We've used it since and it ran the tank, the fridge and the freezer. On the tank, I didn't run the lights, but kept the return pump, powerheads, skimmer and heaters going. We also had an electrician put a "pig tail" on the furnace so it could be plugged in, if needed. We haven't had to try that yet.