Do not wire a 120-volt heater to a 240-volt circuit. The heater will try to deliver four times its rated wattage, causing it to overheat. This will permanently damage the heating element and also void the product warranty.
We do not recommend wiring a 240-volt heater to a 120-volt circuit. The heater will be underpowered and will only receive 25% of the wattage it was designed to deliver.