In Ireland and globally, a key concern is whether energy-efficient buildings truly deliver on their promise of improved indoor environmental quality, enhancing occupant satisfaction and health, while achieving the expected energy savings. This study evaluates the performance of a home in the west of Ireland based on indoor temperature, humidity, CO2 levels and electricity consumption. The home has a Building Energy Rating (BER) of A2, aligning with stringent energy-efficiency standards. This home is evaluated using data collected throughout the year of 2023. Score 1 is the best performing based on the continuous monitoring of temperature and relative humidity to assess compliance with comfort zone (Temperature: 18–24 °C, RH: 40–60%) and an extended acceptable zone (Temperature: 16–26 °C, RH: 30–70%). In addition to these scoring, Time of Wetness (TOW) is also calculated to evaluate the risk of mould development, and CO2 concentrations are also analysed. Further, using the Emporia Vue Home Energy Monitor, electricity data for the entire year of 2023 is analysed to assess energy consumption patterns and performance. The findings demonstrate that seasonal fluctuations substantially influence indoor environmental conditions and energy usage, underscoring the importance of adaptive and seasonally responsive climate control strategies for maintaining thermal comfort and energy efficiency. The framework and results of this study can be useful for evaluating building performance, particularly in scenarios where energy savings are contractually guaranteed also ensuring occupant’s comfort, health, and well-being.