Here in Arizona virtually all the gas furnaces are plug and cord also. The only requirement is the receptacle must be the fused type, with an Edison fuse sized to Article 430.
Our evaporative (Swamp) coolers are also plug and cord connected, right up there on the roof, using a Midwest fused box sort of like a giant bubble cover where the cords hang out the bottom, one for the motor and one for the pump.
And yes, some of our homes are made out of mud.
