I believe that code doesn't allow spark-ignited engines in most cases, if powering life safety equipment. Think it's to do with the complexity.We have a saying in the broadcast world, "Friends don't let friends buy Generac." I prefer Kohler, Caterpillar, or Cummins, and have had positive experiences with all three. Propane is fine for small sizes, but large engines have trouble with a tank vaporizing fuel fast enough without heating apparatus. Natural gas is an alternative to diesel, especially where post earthquake operation isn't a concern. The nice thing about NG is no storage needed.