The Home Energy Rating System (HERS) Index is the industry standard by which a home’s energy efficiency is measured. New homes built in Massachusetts must meet several criteria for energy conservation that are part of the index. The extent to which conditioned air leaks from a home is measured in Air Changes per Hour (ACH) when the pressure differential between the inside and outside of the house is 50 Pascals. The building code requires 3 ACH(50) or less. To meet the Passive House standard it must be less than 0.60. Today, the River House was tested by a certified rater using a blower door test. Our result was 0.36 ACH(50) which is the best score our tester has ever recorded. This means that we have a very air-tight home and since air leakage is the largest contributor to energy loss this will translate to significant energy saving over time.