Cooking using a combustion heat source is the most basic and simplest way to cook. However, the energy efficiency in this cooking process using normal cookware on a gas range is poor, typically utilizing only 30% of the energy generated by the flame. This is mainly because the convection heat transfer from the flame to the cookware is inefficient; the hot gas escapes over the side of the pot. This is the technical reason for the idiom “A watched pot never boils”.