I'm looking to replace my existing water heater with a more efficient model. One of the things that makes better models more efficient is the replacement of the thermocouple / pilot control system with electronic control and ignition plus electrically controlled dampers. Thus the heater requires some form of electrical hookup for this function.
My understanding is that in this scenario code requires the gas furnace and gas water heater to be on dedicated circuits. (Is my understanding wrong?)
I'd rather not (pay someone to run) a whole new circuit when I'd expect the water heater to need less than 4W. As a result I'd like to reuse the furnace's circuit and install a SPST switch and plug combination in the junction box where the furnace's existing disconnect switch is located, and connect the water heater to it.
How worried should I be about this? Am I going to cause serious safety hazards or equipment damage?