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My following comment is from the perspective of an informed user, and experience.
I have a 200 A panel. Under normal typical daytime use my power consumption is usually below 3 kW. You can see plots of this at
http://beta-a2.com/energy.html . Not all of this load is necessary under emergency conditions. I have a 5 kW Honda as a backup and it is adequate for my real necessary electrical needs. It is still a gas hog. Probably between 5 and 10 gallons per day.
What do I really need to run. One refrigerator, two freezers, furnace fan motor, TV, radios, some lights, and various computers. Besides these I have also run the washing machine motor, and the dryer motor.
If all motors do not come on at once my generator can handle the inrush currents. So on starting up the generator one sheds loads.
If someone were trying to sell me a backup generator they would probably be suggesting upwards of 15 kW. How often do I need this backup? Not often. Within the family we have four generators of about comparable size, three houses and a shop. Can not power much at the shop, but can run computers and lights.
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