How can I effectively use an immersion heater for a bathtub to ensure a comfortable and relaxing bathing experience?

To effectively use an immersion heater for a bathtub, fill the tub with water to the desired level, then submerge the heater and turn it on. Monitor the temperature to ensure it doesn't get too hot. Once the water reaches a comfortable temperature, you can enjoy a relaxing bath. Remember to follow safety guidelines and never leave the heater unattended.