Question:  I need a backup generator in case my power goes out at home, but I'm not sure exactly what size to buy.  It needs to run a refrigerator, one or two circuits of house lights, our furnace and maybe my electric range.  I can afford a portable generator, but not a home backup unit.  My budget is around $1000.

Answer:  You will need at least a 8kW genset, which is a total of 33 amps maximum output. The refrigerator takes about 15 amps to start, the lights 15 amps with them all on, and that leaves a single circuit of 15 amps at 240 volts to run your furnace. Since a generator should never run at maximum load at all times, figure that a typical load of 60% is what you will want to run.  A single burner on a range is typically 1500 Watts or 12.5 Amps and the oven (bake unit) is 5500 Watts or 46 Amps, so to run the electric range you'll need significantly more power. If your furnace is a gas furnace with 120 volt power, 8kW would be large enough to do what you want. If you want to add a heat pump or A/C unit, you will need at least a 20 KW unit.

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