Mine can use natural gas as well. And I had the electricians hook up a auto double throw switch to the main grid switch rather than using the smaller panel. It senses when I lose power and then there's a small wait for 'brown out' - 30 seconds? and then it automatically switches over. I did a 'wattage survey' before and I can run anything in the house, except I couldn't have the oven and all the burners on the stove on at the same time

. But AC, heat, tv, sump pump, computer, coffee maker - all work well. I had an 8 hour outage the first year I installed it and 4 other incidents not that long. Nothing last year... and once this year. It runs every Wednesday off line as part of the maintenance cycle. It's loud but I'm back in the woods...
I got a good deal on it - a friend had a nephew working for the company - Bryant (although the internals are generac) and they had a 'friends and family' sale. It cost me more of the electricians installing it than for the unit.