Controlling power for tank-less heater like the Panasonic DH-6SM1

i’m looking for a way to control the power for my tank-less water heater, Panasonic DH-6SM1.

the use case i have in mind is to power on the heater along with the lights and exhaust fan in the bathroom when someone is in the bath and then automatically turn it off when the room is empty. to complicate matters, locally neutral wires are not common in houses.

am still googling gear up but wanted to see if other folks have solved a similar issue.