Around here, we hard-wire gas furnaces, with a single-pole switch as a disco. I don't know why it wouldn't be OK to do it with a cord-and-plug connection, as long as the cord is kept away from the flame. Yes, 400.7 does cast doubt on the legitimacy of that, but you have to admit, it would give people one less reason to backfeed their houses with portable generators, if they could simply plug the furnace into the generator.
