This book begins by discussing the way in which designing district heating systems to operate below 167F (75C) reduces the overall delivered cost of heat by reducing the capital cost of the heat source, allowing for the use of non-traditional and renewable sources, reducing the cost of piping, and allowing for the use of large-scale thermal storage. The authors describe the development of the provisions of the European Union law which apply to district heating to examine the particular legal acts in force, and provide an outlook on future developments. In closing, an experimental investigation is presented on a closed-loop earth-to-air heat exchanger (underground air tunnel) in heating mode.