BPI Certified: The Building Performance Institute (BPI) is the nation's leading building science accreditation organization. This organization teaches the "house as a system" philosophy - which looks at a building's various components (building envelope, attic, basement, combustion equipment, ventilation sources) and the interrelationship between them to maximize a home's performance. This approach leads to greater energy efficiency, but perhaps more importantly to buildings that simply work better. A home that has been analyzed and upgraded from a whole-house standpoint is more durable, healthier, more comfortable, and more energy efficient. For more information about BPI's standards, take a look at their Technical Standards for Building Analysts (PDF).
We were very happy with the work by ERS. From the initial evaluation to the completion of the work, Paul Swenson and his crew were a pleasure. We learned a lot about our house in the process, and feel confident that we'll head into this winter with a much more energy-efficient home. I recommend ERS without hesitation.