In the AEO2006 Reference Case, total delivered energy consumption (excluding electricity losses) for the residential sector in 2005 was estimated to be nearly 12 thousand trillion British thermal units (Btu) provided to more than 115 million households^[3]. Natural gas and electricity were the leading sources of energy for the sector, followed by petroleum. Wood space heating consumption was 430 trillion Btu, while solar thermal and PV together were 25 trillion Btu. GHPs provided 3 trillion Btu (Table 1). Information from external sources on pellet fuel, small wind turbines, and direct geothermal use is contained in the "Analysis Caveats" section of this report.