I saw a writeup where a gas furnace was wired with a piece of an extension cord with a plug (properly sized) that was then plugged into an outlet (dedicated circuit). There was only one outlet so only one device could be plugged at a time. This would allow the furnace to be easily switched to a generator in case of a power failure. This was said to be NEC compliant as the circuit was dedicated for the gas appliance and the wiring/outlet was sized properly. This seems like a much simpler and cheaper approach than a transfer switch but before I go and do this I wanted to be sure this was a sound idea.