This paper aims at presenting a method for identifying, characterising and quantifying the available waste heat of an industrial system that can be converted into a useful form. A distinction is made between avoidable and unavoidable waste heat. This distinction is especially important when it comes to deciding on an investment for the integration of a waste heat valorisation process. In the proposed methodology, process integration techniques and exergy analysis are used to measure the useful potential of waste heat. It results in a definition of waste heat as a resource and a reserve in analogy to the definitions of natural resources and reserves. © 2013 Published by Elsevier Ltd. All rights reserved.