By code, 20 Amps x 80% = 16 Amps max allowable.
16 Amps x 240 Volts = 3840 Watts max.
If you use a 100% rated breaker the max Watts is 4800 Watts.
Good luck finding a 20 Amp breaker rated for 100%.
-------------------- Ohm's law
Not just a good idea; It's the LAW!