We just discussed that in this thread No shut off switch for furnace - #68 by rmeier2
Apparently the electricians here do not think that a furnace has any vibration. As a result it is not eligible to be powered by a flexible cord. I don’t think they’ve ever installed a blower motor or used one on the floor of the shop for cool air in the summer (would walk across the floor slowly).
Wouldn’t fly around here. Agents will rip code to shreds (something about somebody’s grandfather). Hard sell with contractors if the AHJ passed it. might sound OK to buyers until one of the two corrects it. If it’s not done right you need to be able to call it out as a safety issue.