I have a 240V 2000 watt heater. The double-pole thermostat says 17A. 2000 watts divided by 240 volts equals 8.33 amps, so why does it say 17? Apparently 17 is twice 8.33; is that the cumultative amperage rating? Thanks

As you calculated the heater will draw 8.3 amps.

The thermostat is a switch that can handle up to 17 amps, and no more.