Currently, the conventional design method for ASHPs is only to ensure that the required output heating capacity at specific rated conditions can be provided, without considering the impacts of frosting on the operating performances including the output heating capacity of ASHPs when operating at different regions with different climate conditions. Therefore, in this paper, a novel design method for ASHPs considering both the required output heating capacity and frosting suppression has been proposed, and its development is reported. A prototype ASHP air heater for use in the cold and frosting regions in China was designed using the proposed design method, and tested in both laboratory and field. The laboratory test results showed that the prototype ASHP air heater could both provide the required output heating capacity of 3 kW at its rated condition of -12 °C DB / -13.5 °C WB, and achieve the desired level of mild frosting at the standard 2 ^oC DB / 1 ^oC WB frosting condition. Furthermore, the field results indicated that the prototype ASHP air heater could maintain a better operating performance due to better frosting suppression than a conventional ASHP air heater with the same rated capacity of 3 kW. The COP values of the prototype ASHP air heater were 21% ~ 37% higher than those of the conventional ASHP air heater. The test results suggested that the novel design method could be used to help design ASHPs that can not only provide the required output heating capacity at rated condition, but also achieve a desired level of frosting when operated at different frosting regions.