What efficiency standard must HVAC systems meet to positively influence HERS ratings?

The efficiency standard that HVAC systems must meet to positively influence HERS ratings is based on Seasonal Energy Efficiency Ratio (SEER) values for air conditioning and Annual Fuel Utilization Efficiency (AFUE) for heating systems. SEER measures the cooling output of an air conditioning system over a typical cooling season divided by the total electric energy input during the same period, highlighting the system's efficiency in cooling. AFUE, on the other hand, represents how efficiently a gas furnace converts the energy in its fuel to heat over the course of a typical year.

Both ratings are significant in assessing the overall energy efficiency of HVAC systems, directly impacting the calculations and scores assigned in the HERS Index. Higher SEER and AFUE ratings are indicative of better efficiency, leading to lower energy consumption and environmental impact. This correlation results in more favorable HERS ratings for homes equipped with HVAC systems that meet or exceed these standards.

The other options, while they mention relevant efficiency metrics, do not encompass the two key standards (SEER and AFUE) that directly influence HERS ratings. Therefore, focusing on those specific metrics presents a clearer guideline for what positively affects the HERS score.