The study analyzes the impact HVAC system tune-ups and equipment replacement has on HVAC system distribution effectiveness, residential energy efficiency, and indoor air quality. Data analyzed in this study is from Iowa's HVAC System Adjusted and Verified Efficiency (SAVE) program. This program, established by the Midwest Energy Efficiency Alliance (MEEA), creates a network of HVAC contractors trained to easily diagnose the performance and measure the in-place efficiency of functioning HVAC systems. HVAC SAVE certified contractors measure static pressure, system temperature, and airflow to identify existing system deficiencies, allowing them to make targeted repairs or adjustments. This study answers two primary research questions: (1) What is the current installed HVAC system operating efficiency, as defined by the quantity of conditioned air reaching building occupants?; (2) What improvements in HVAC system operating efficiency can be achieved from common modifications and quality installation of replacementequipment?

From the data collected, this study determines that homes which have undergone HVAC SAVE certified performance testing and have carried out a system tune-up or equipment replacement experience significant improvements in HVAC equipment operating efficiency and HVAC system distribution efficiency. In addition to improving heating and cooling system distribution effectiveness, HVAC SAVE improvements have a positive impact on the home's indoor air quality. For instance, HVAC SAVE system tune-ups, can significantly improve the air mixing and dilution ventilation and thus improve indoor air quality. The results identified in this study support the idea that residential heating and cooling equipment should be tested and improved as a system rather than a collection of individual components in order tomaximize heating and cooling efficiency and improve indoor air quality.