That should be controlled by the NRTL that listed it. If it was really a 13a load it should have a 5-20 plug ... but that is far from certain. I have a U/L listed 1650w smoker with a 5-15 plug.
It has tripped breakers and burned up plenty of cheap receptacles before I inherited it.
I use it on a dedicated spec grade 5-20 with no problems.
