The number one question we were asked throughout the BuildingEnergy Boston show was, "Can I use an air-to-water heat pump to replace my boiler?" to which we answer "Yes - but it's complicated". This session would give the necessary space and time needed to explain and demonstrate the nuances involved in this surprisingly simple solution. The reason this question is specifically so crucial right now is because of the prevalence of steam heating systems and boiler systems that make up the existing building and housing stock, specifically in NYC as well as much of New England. Air-to-water provides a promising solution that allows us to make use of what already exists, and retrofit the systems in a way that future-proofs them against continuously changing regulations and technologies. Water-based systems are as old as the Romans, and provide decades upon decades of lasting reliable comfort. With monobloc air-to-water heat pumps all refrigerant comes pre-charged and remains packaged in the self-contained unit that sits outside, reducing the high risk of devastating damage direct to the ozone that results from pin-hole refrigerant leaks in air-to-air systems. According to some sources, approximately 10% of air-to-air systems end up with leaks. In addition, due to evolving refrigerant regulations, air-to-air systems are therefor a temporary technology, because in the future refrigerant upgrades will force them to be completed replaced with and upgraded.