In this study, the performance of R170/R1270 mixture was measured on a heat pump bench tester to substitute for R22. The tester was equipped with a hermetic compressor providing a nominal capacity of 3.5 kW. All tests were conducted under typical summer and winter conditions of 7/$45^{circ}C$ and -7/$41^{circ}C$ in the evaporator and condenser, respectively. During the tests, the composition of R170 varied from 0 to 10% with an interval of 2% for the R170/R1270 mixture. Test results showed that the capacities of the R1270 and R170/R1270 mixtures were 3.2-10.0% and 4.2-20.4% higher than those of R22, respectively. The coefficient of performance (COP) of R1270 was 2.7-3.6% higher than that of R22. On the other hand, the COP of R170/R1270 mixture decreased at a constant rate as R170 was added to R1270. The COP of R170/R1270 mixture was similar to that of R22 at 2% R170 and then became lower than those of R22 as R170 increased. For the mixture, the compressor discharge temperature was 8-$20^{circ}C$ lower than that of R22. The amount of charge was reduced up to 55% compared with R22. Overall, pure propylene and R170/R1270 mixtures are good long-term candidates from the viewpoint of energy efficiency and greenhouse warming to replace R22 in residential air-conditioners and heat pumps.