There are two dominant certifications in the United States for home energy auditing. They are BPI Building Analyst Professional and RESNET HERS Rater. Many people confuse these standards, but the difference is simple.
BPI stands for Building Performance Institute. The Building Analyst Professional certification is used for existing homes. An energy auditor does an evaluation of energy consumption to determine ways in which energy can be conserved.
The RESNET HERS Rater distinction is for Energy Star New Homes. Before the builders have put their finishing touches on the home, the RESNET HERS Rater may evaluate the home for insulation gaps. In general, it is much easier to evaluate for insulation gaps at this stage in the game. It is much harder to do when the home is completely built and lived in.
There was a time when the BPI Building Analyst Professional certification was more popular, but more and more people are becoming interested in RESNET now. I’d say the certifications are equally popular now.