Heating are weaves in the One Power.
Heating a liquid
This is a very simple weave, formed by flows of element Fire. For example a very tiny thread of Fire is used by Aes Sedai to heat the water inside a teapot. A more powerful weave of this kind was used by Elayne to heat the water in a bath tube because it was becoming cold.
Heating the air
It is formed by flows of Air and Fire. It was used by Rand on the top of Dragonmount to warm the very cold air around him.