The waves that are called waves of heat energy are infrared waves.

Infrared waves are a type of electromagnetic wave that has a longer wavelength than visible light. These waves are not visible to the human eye, but we can feel their effects as heat. Infrared waves are produced by the vibrations of atoms and molecules, which generate thermal energy.

Option 1, radio waves, are a type of electromagnetic wave with a much longer wavelength than infrared waves. They are commonly used for communication purposes, such as radio and television transmissions.

Option 3, ultraviolet waves, have a shorter wavelength than infrared waves. They are known for their ability to cause sunburns and damage to the skin. Ultraviolet waves are also used in various applications, such as sterilization and fluorescent lighting.

Option 4, microwaves, have a shorter wavelength than radio waves and longer wavelength than infrared waves. They are commonly used in microwave ovens for heating food.

Therefore, the correct answer is option 2, infrared waves, as they are specifically known as waves of heat energy.