Toller wrote:

They say it draws 18a and can be run on a 20a circuit, but they
suggest a
30a circuit.

"They" don't have a clue if they suggest a 20A c'bkr.

You need 30A.

Thermal/Magnetic c'bkrs are designed to operate at 80% of rating on a
continuous basis under normal ambient temperatures.

Lew