Based on the analogy between electricity and heat, we find that electric transformers and heat exchangers have many similarities. However, unlike transformers where V-o can be higher than V-i, the outlet temperatures of conventional heat exchangers are limited (i.e. T-c,T-o < T-h,T-i T-h,T-o > T-c,T-i). Therefore, the effectiveness of a heat exchanger cannot exceed unity. Such limitations make it difficult to identify and evaluate thermal equipment or systems for many applications. For example, in city central heating systems, in order to reduce the flow rate of the heat transfer fluid in the primary heat network, m (energy consumption for transporting the fluid is proportional to m(3)), T-h,T-o is often expected to be lower than T-c,T-i. In this case a traditional heat exchanger cannot meet this requirement. How to conveniently identify or evaluate the most suitable system for such applications is an important but unsolved problem. In this paper we propose a new concept, the heat adaptor, to address this problem. The idea is to combine heat-work conversion equipment (heat engines and/or heat pumps) with conventional heat exchangers. Using this concept, a typical process of a heat adaptor is established and its thermal performance is analyzed. The results show that the best process and best device arrangement can be obtained for given conditions, and that the thermal performance of these processes can be evaluated. (C) 2013 Elsevier Ltd. All rights reserved.