Life Cycle Assessment of an Air-Source Heat Pump and a Condensing Gas Boiler Using an Attributional and a Consequential Approach

Emissions from heating systems in the building sector significantly contribute to anthropogenic environmental pollution in Germany. Heat pumps are often considered to reduce these pollutions. Therefore, the aim of this study is to compare the environmental impacts of an air-source heat pump with the most commonly used technology, a condensing gas boiler. For this purpose, a comparative life cycle assessment is used. To determine the life cycle inventory of the use phase, an energetic simulation is carried out for both heating systems, with a new single-family house serving as the reference building. The gas boiler is beneficial in 8 out of 11 impact categories. However, the carbon intensity of 76.9 g CO₂-eq/MJ heat is 15% higher than for the heat pump. Most environmental impacts for both heating systems occur during operation. The application of the consequential life cycle assessment approach leads to an average reduction of 46% in the environmental impact of the heat pump compared to the attributional approach. In contrast, the gas boiler is only slightly affected by changing the modeling approach. Nevertheless, the heat pump still has higher environmental impacts in 7 impact categories compared to the gas boiler. However, since the reduction of greenhouse gases of the natural gas-fired system is limited, the carbon intensity of the air-source heat pump is 70% lower compared to the condensing gas boiler.