That's a good idea in theory, but you'd have to block off all the 120V outlets on the same circuit. If the existing breaker is 15A, you need a NEMA 6-15, which

That's a good idea in theory, but you'd have to block off all the 120V outlets on the same circuit. If the existing breaker is 15A, you need a NEMA 6-15, which is 2.9 kW.