Air-to-water (A/W) heat pumps provide an efficient and established alternative to fossil-based heating systems in moderate climates. However, in cold climates building demand increases and low source temperatures lead to deterioration in heating capacity and efficiency of A/W heat pumps. The present study investigates the performance enhancement of A/W heat pumps operating in cold climates. Using steady-state simulations with RefProp and R290, three single-stage A/W heat pump concepts—incorporating an internal heat exchanger, an ejector and an expander, respectively—are compared to the standard cycle. The steady-state simulations assume constant isentropic and volumetric compressor efficiencies of 0.65 and 0.85, respectively, a temperature difference of 5 K on the heat source and the sink side, and 8 K superheat. Performance is evaluated across a range of source temperatures \(({-22}\,^\circ {\text {C}}\) to \({12}\,^\circ {\text {C}})\) and sink temperatures \(({35}\,^\circ {\text {C}}\) to \({65}\,^\circ {\text {C}})\) . The results indicate that the ejector cycle exhibits superior performance, addressing all three target figures at the same time. At \({-22}\,^\circ {\text {C}}\) source and \({65}\,^\circ {\text {C}}\) sink temperature, the ejector cycle achieves a 36.3% increase in volumetric heating capacity, 9.2% improvement in coefficient of performance and a 15.8 K reduction in the maximum compressor discharge temperature compared to the standard cycle. Future research will focus on experimental validation of these simulation results and a comparative analysis with (quasi-)two-stage heat pump concepts to explore further performance optimization strategies.