In many cities, multifamily buildings are the largest emitters of greenhouse gas emissions. To meet our decarbonization goals, we need to increase focus on electrifying existing multifamily buildings, but transitioning these buildings to highly-efficient electric systems is complex. Central heat pump water heating systems are pivotal to electrifying multifamily (and commercial) buildings, but these systems have numerous design and installation challenges that can sink a project if not adequately understood and accounted for. Through AEA’s work on cutting-edge early-stage demonstration projects, we have learned many of the lessons the industry will need to understand in order to deploy these clean-energy systems at scale and meet our climate commitments in New York and beyond.