As there is currently a lack of reliable guidance for investors to make the most sustainable choice when it comes to different renewable heating technologies for residential buildings, this contribution presents a methodological approach for a comprehensive comparison, while also addressing data requirements. A focus point of the methodology development and the sustainability assessment lies on the integration of a dynamic electricity mix to account for the continuous decarbonization in an energy grid that is more and more based on renewables. Its influence on the final environmental impact results of the presented exemplary system combining a solar thermal collector and an air source heat pump is assessed. The results indicate a significant influence of the electricity mix on the carbon footprint (- 48%) of the provided heat. The resource use is only slightly changed (+ 3%).