The district heating (DH) industry has been characterized by continuous innovation for several decades, but there is limited knowledge on the characteristics of the sector’s innovation activities, arguably the most important information for understanding how the sector can continue to develop and further support the energy transition of society. We perform a systematic literature review (SLR) to identify the types of innovation, the levels of innovation and the relation between different innovations in the DH sector. A total of 899 articles are analyzed and coded into eight groups: fuel, supply, distribution, transfer, DH system, city system, impact and business. Most of the articles (68%) were identified in the groups: “supply”, “DH system,” and “impact”, with a focus on DH from a system or production perspective and its environmental impact. We find that there is limited research on DH firms” challenges, including management perspectives, such as asset management and customer focus. Despite this potential, we find only a limited number of articles related to innovation. Not much scholarly attention has been given to areas of large cost-saving, especially capital cost. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.