The thermal efficiency of the cooker is over 40%. Compared to the traditional three-stone fire (with 10% efficiency), firewood consumption is reduced to less than a quarter (75% saving). When the Heat-retention cooking is applied additionally (see: Imma and Dieter Seifert: Notes on Fireless Cooking - Cooking With Retained Heat), the firewood consumption drops to about one-seventh. This small amount of wood can be provided by plantations, which can be harvested annually. Thus, the search of firewood and felling of trees is completely avoided.