To reach a maximum of production rate and energy efficiency any industrial process technology typically has to be optimized regarding process specific requirements. So any system for thermal processing needs to be adapted to the required production rate and to the material specific thermal properties of the products to be processed. High power microwave technology used as an alternative heating source has been demonstrated to provide potential process enhancement in various fields of applications. Nevertheless the system optimization for a real industrial and viable process design is significantly more challenging in case of microwave assisted processing. Beside the heating uniformity the knowledge of materials specific microwave properties is essential for an energy efficient design of an appropriate applicator. A simple analytical model has been developed enabling quick and crucial insights into system efficiency and its correlations to applicator size, microwave coupling as well as dielectric properties and size of materials to be processed. Furthermore the suitability of this model has been tested by systematic experimental investigations and full 3D electromagnetic simulations on large scale and untuned multi -mode applicators.