Generac 20 KW, runs off natural gas, automatic start and stop, test runs once a week, can run the entire house as long as we don't use ALL major appliances at the same time. An electric oven and stove are very heavy electricity users. Uses an air cooled motorcycle 999cc engine. Installed cost was ridiculous at $12K but we're very happy with it.edited:  
rices are higher before and during hurricane season. Winter purchases might save you a few grand. 4951