Maximizing energy efficiency of buildings is essential to meet EU climate targets and strict national regulations. We examine how local climate influences energy performance of residential building and mitigation options. A model of single-family house was analyzed in whole year energy simulation software WUFI Plus. Three Polish locations were investigated, namely Wrocław, Warszawa and Kołobrzeg. Implementation of the original meteorological dataset into WUFI Plus based on typical meteorological year (2005–2023) is a novel element of this work. Hourly heat and mass transfer, usable, final and primary energy indicators, and CO2 emissions were calculated for a gas-boiler baseline and two alternatives: an air-to-water heat pump, and air-to-water heat pump with photovoltaic panels. Results for the gas-boiler scenario show location-dependent heating demand differences up to 30%; usable energy for heating ranged from 7561 to 9760 kWh/year, and EP of the system from 114 to 129 kWh/(m2·year). Replacing the boiler with an air-to-water heat pump reduced final energy indicator by over 60% but produced similar CO2 due to Poland’s carbon-intensive electricity mix. Adding photovoltaic system, that covers electricity demand only of auxiliary equipment, cut CO2 emissions by about 10%. These findings highlight the importance of climate-specific meteorological inputs and on-site renewables to meet forthcoming energy performance standards.