You have the idea right but what you are saying is not exactly correct. Heater loads are purely resistive and linear unlike motors which are inductive loads. The Ohm's Law formula used with heaters to calculate how voltage, current, resistance, and wattage react with each other. Without going to far into the details since unlike heaters, motors are inductive loads making them non linear which causes them to react to current, voltage and power differently than heaters.
Heater loads being purely resistive making them very simple.
Ohm's Law:
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Using Ohm's Law you will see for a given resistance of the heater, voltage and current are directly proportional.
Residential Example:
Let's say you have a 10kW heater in an electric air handler to heat your house. When you apply 240V across the heater it will draw 41.66A. When you apply 120V across the same heater it will draw 83.32A.
When you pay for your electricity you are pretty much paying for Amps. So anytime you can use 240V in a residential application you save money.
