This study reports the application results of an air source heat pump (ASHP) for heating in Harbin, the coldest provincial capital of China. These include the heating temperatures, system COPs (coefficient of performance), and frost characteristics of the ASHP operated in three cold days. The results show that the ASHP showed high heating temperatures of 21.9-27.3 degrees C for the three days, as the indoor air had high temperatures of 19.8-24.2 degrees C. The ASHP showed low COPs of 1.04-2.44 for the three days, mainly resulting from the high indoor temperatures of 19.8-24.2 degrees C and low outdoor temperatures of -20.9 to -10.4 degrees C collectively. Although the ASHP system had low COPs, no obvious frost phenomena were observed on the surfaces of the tubes and fins of the evaporator located in the cold outdoor air, mainly due to the low relative humidities of 27%-37% for the outdoor air. The results obtained from this study show that ASHPs can be used for heating applications in cold regions. However, the difference between indoor and outdoor air temperatures should be controlled within 41 degrees C to achieve an acceptable COP. (C) 2016 Elsevier B.V. All rights reserved.