Indoor Environmental Quality (IEQ), Life Cycle Assessment (LCA) and Life Cycle Cost (LCC) were assessed in an office case study building with varying thermal mass, technical systems, and internal loads. A radiator system and an active chilled beam system, both using VAV, were tested. The impact of different reference study periods (RSP), operational emission factors and occupancy schedules, was quantified. IEQ was used as a prerequisite to ensure realistic energy use in combination with LCA and LCC. With an RSP of 50 years and 2023 emission factors (baseline), the average whole life carbon emission was 9.1 kg CO2-eq./m2/year. A shorter RSP resulted in an average increase of 13%. 2030 emissions factors decreased the average by 28% and 15% for a RSP of 50 and 41 years, respectively. The average operational emissions contributed 41.2% of the baseline’s total whole life carbon emissions, and embodied HVAC-specific emissions were 11.6%. Using 18 different countries’ load schedules, the maximum operational emissions’ contribution was 48.8%. The LCC was found to be 353.4 DKK/m2/year and 424.6 DKK/m2/year for an RSP of 50 and 41 years, respectively. Operational energy contributed up to 8.5% of the total cost, and HVAC systems contributed 23%. Cases with high thermal mass showed a higher cost and greater carbon impact, than low thermal mass cases. Changes in energy use had more impact on the LCA than the LCC. This study’s methodology effectively combined IEQ, LCA and LCC for future decision making and building design.