A cast of experienced building energy geeks discuss measured performance of air source heat pumps and best practices for installation. With so many ASHP systems going into new buildings, we keep learning new information and new ways to make mistakes. We want to share this knowledge to save at least a few stubbed toes! We have logged energy usage of several air source heat pump systems, including multi-head systems, and from the data estimated system COP under a variety of weather conditions. We will focus on the data and then zoom out to implications for best practices.