High-performance HVAC systems optimize energy efficiency and comfort, especially when coupled with building envelope upgrades like improved insulation and air sealing. Test-in/test-out procedures assess the impact of these upgrades by measuring energy performance and indoor air quality before and after implementation. This ensures significant energy savings and improved occupant comfort. By collectively implementing better HVAC systems and upgrading building envelopes, we raise the bar for a higher standard of energy efficiency and comfort in buildings, contributing to a more sustainable future.