These data underpin a scenario analysis of U.S. building energy use, emissions, and costs out to 2050 using Scout (scout.energy.gov), a reproducible and granular model of U.S. building energy use developed by the U.S. national labs for the U.S. Department of Energy's Building Technologies Office (BTO). The scenario analysis explores uncertainty in the progression of both U.S. energy demand- and supply-side conditions that affect U.S. building energy use and CO2 emissions out to 2050. For electric power supply, we consider two levels: one corresponding to the 2020 AEO reference case ("RB"), and another corresponding to the 2020 AEO low oil and gas supply side case ("HR"), which achieves a higher level of renewable electricity penetration—approximately 53% of total power generation by 2050 compared with 38% in the reference case. Three different sets of energy conservation measures (ECMs) are considered across the scenarios. The performance guidelines ECM set ("1T") includes currently available technologies that meet existing codes and/or voluntary recognition programs (e.g., ENERGY STAR). The best available ECM package ("2T'') includes the most efficient commercially-available technologies per EIA data and other sources. The prospective ECM package ("3T'') includes research-grade technologies that could be released over the next decade as outlined by the BTO Multi-Year Program Plan and the more recent BTO Windows, Envelope, and Sensors and Controls Roadmaps. Finally, we explore two levels of technology switching from on-site fossil fuels to electricity: the basic level ("FS0'') introduces fuel switching without any incentives; and the incentivized level ("FS20'') reduces the installed cost of fuel switching measures by 20%. Scenario results are provided on a site energy basis (“Site Energy” folders within the results for each scenario) and source energy basis (“Source Energy” folders), where the latter is calculated using the captured energy method. New in Version 3: Updated Scout version to 0.6 (utilizes site energy data, technology cost, performance, and lifetime data, site-source energy conversion factors, greenhouse gas emissions factors, and technology adoption model coefficients from the 2020 AEO reference case, except for the “HR” scenarios, which include supply-side assumptions that represent the 2020 AEO low oil and gas supply side case). Updated performance guidelines ECM set to conform to the latest versions of ENERGY STAR specifications and IECC 2021. Reintroduced the following fuel switching ECMs. The NVC and AVCT HVAC ECMs were modified with the assumption that heating performance COPs are half that of cooling COPs, which are assumed to be those targeted by the BTO MYPP: Prospective Residential Integrated ASHP (FS) Prospective Residential NVC HVAC (FS) Prospective Commercial NVC HVAC (FS) Prospective Residential AVCT HVAC (FS) Prospective Commercial AVCT HVAC (FS) Revised market entry years to 2021 or later for all ECMs. Updated ASHP, ASHP FS measure market scaling fractions to ensure consistency with 2015 RECS and 2012 CBECS building equipment stock data. Expanded the application of residential ASHP measures to encompass homes with electric resistance heating and central AC units. Previously, these measures had been limited to replacing existing heat pumps. Changed HR case site-source data to represent the AEO 2020 low oil and gas side case, in which renewable penetration reaches 53% of electricity generation by 2050. Previously, the 2018 AEO $25 carbon allowance fee side case was used (45% renewable penetration by 2050). Provided a parallel set of results for scenarios 1–8 (available in the folder ./Results/ECM Performance Improvement), in which it is assumed that the performance and cost characteristics of ECMs in the 1T and 2T packages change over time; rates of change are consistent with that of comparable baseline technologies in the 2020 AEO reference case.