Jim DeLaney, Austintown, Ohio
I have a 12KW Generac that powers pretty much everything in the house, except the Air Conditioning. It's wired through a transfer switch, and kicks in after a short (15 seconds?) delay after the power goes out.

Coincidently, we had a storm yesterday that took the power off for about six hours. We were the only house in the neighborhood with power, thanks to the Generac.

Mine is natural gas fueled. Hookup required a permit, a licensed plumber for the gas hookup, and a licensed electrician for the electrical work.

There are also restrictions regarding locations of the unit with respect to eave overhangs, proximity to windows, etc., so check with your local code folks for what you'll need.