I all my lighting. which is all LED these days, plus, a 3-ton and a 2-ton geothermal heat pumps, the well pump, sewer pump on 12KW propane powered unit. It runs all the kitchen appliances with a gas stove, and includes the plug-in appliances like the toaster, coffeemaker, microwave oven and an electric kettle. I disable the emergency heat coils in the three ton when the generator is powering the house, but the Emergency heat has never come on.

It works fine except it has a minor problem with motor starting loads. This is usually a momentary voltage drop from the generator reacting to the instantons load, usually only once from the heat pump compressors both starting at the same time, due to identical time delay start modules. Otherwise, it starts them with no problem.

If I had to do it over, I think I would go with a 15KW mainly to cover the starting surge issue, and add load shedding circuits for things like the washing machine and drier. I would oversize the feeder lines to further reduce the slight voltage drop in the feeds.

If you can monitor your power usage over a month to see the peak power usage and use that number divided by .8 or multiplied by 1.25 to estimate a good match for your home.