Thermal transmission through translucent façades is the primary source of energy consumption in buildings. A vacuum-glazing insulated water-flow window (VWFW) offers improved thermal insulation and enhanced solar water preheating performance. This paper explored the effectiveness of vacuum-glazing (VG) insulation in a water-flow window (WFW) and the energy-saving performance of a VWFW compared to a common double-glazing water flow window (DWFW). This comparison was conducted based on experimental and numerical analyses.The results revealed that with VG insulation, the annual heat gain of a room through the window was reduced by 50.3% compared to that measured with a DWFW. Moreover, the interior glazing surface temperature of the VWFW was more stable and closer to the room temperature set-point. Monthly average water heating efficiencies of 40% and 34% were obtained for the VWFW and DWFW, respectively. WFWs can be applied as energy producers in building. The advantages of VWFWs include improved electricity savings and reduced carbon emissions. These values were found to be 78.34 kWh/m2 and 69.8 kg CO2-eq/m2, respectively, for the VWFW, while those of the DWFW were 33.67 kWh/m2 and 30 kg CO2-eq/m2. The use of VWFW is thus meaningful for further reducing building-related energy consumption and reachingcarbonneutrality.