Heat is transferred as a result of the generation of steam to a process. The three methods (or modes) of this transfer are radiation, convection and conduction, and these occur either between or within different substances. The overall heat transfer will be the sum total of the heat transferred within or between substances, as a result of these three modes.

If a stationary or a solid fluid substance has within it variations of temperature, heat will be transferred from one area to another and the process will be called conduction. In the fluid, adjacent molecules will tend to collide with one another and in so doing, a transfer of energy will occur from more energetic molecules to less energetic ones. The molecules with more energy are the ones at the higher temperatures, and because of that the conduction that occurs will flow to the molecules that are at lower temperatures.

Convection occurs when heat energy is transferred between a liquid in motion and a surface, and when both are at different temperatures. It represents the combination of the mass motion of molecules and the process of diffusion.

A great deal of molecular motion occurs randomly at the surface of the fluid where velocity of the fluid is low. But further from the surface, the bulk motion that occurs, affects this process, and the transfer of convective heat occurs either by natural or by forced convection. Buoyancy factors and differences in densities resulting from temperatures changes, give rise to the natural convection process. However, forced convection will happen as a result of an external force like an agitator or a pump. A phase change like condensing or boiling that result in heat energy transfer is a convection process.

In the process of radiation, heat is transferred when electromagnetic waves (otherwise called thermal radiation) is emitted from a surface. Here heat transfer will occur between surfaces whose temperatures differ. The transfer actually occurs efficiently in a vacuum, and does not require the presence of a material medium.