A one-to-one equipment swap with air source heat pumps, which is typically the first full electrification option considered, may not be a realistic decarbonization strategy particularly for owners of large buildings facing various constraints around thermal distribution systems, roof space, tenant disruption, and energy supply. In fact, we are suggesting you determine the building’s need for heat pumps toward the end of the decarbonization road mapping process so these heat pumps can run optimally. Significantly reducing loads, recovering and reusing heat wherever possible by enabling thermal networking, and using a cascading approach to decarbonizing easy-to-electrify loads is likely advantageous. Systems should be optimized to deliver heating or cooling efficiently over the integrated sum of the year’s diverse conditions, the vast majority of which are at part-load. Efforts to reduce and shift loads can help reduce peak capacity, and electrification of more difficult peaks may require special consideration within the building’s roadmap and taking a rational approach to resilience and accounting for evolving electric grid or thermal network supply conditions. This is the foundation of Resource Efficient Electrification (REE).