The rearchetected system uses updated carbon emissions factors from those in the legacy system. At present this is used only by the Home Energy Scoring tool.

To arrive at the carbon emissions (as CO₂) for energy consumed in the user’s house, we multiply the annual energy for each fuel type by the emissions factor for the respective fuel:

emissions = sum (site energy[resource] * carbon_factor[resource])

     where: resource = electric, natural gas, fuel oil, lpg

Table 33 presents the emissions factors for fossil fuels. Natural gas and fuel oil emission factors are derived from U.S. DOE (1994), while the LPG emission factor is from U.S. DOE (1996).

Table 33. Direct Carbon Emissions (as CO₂) from Residential Fuel Combustion

Fuel	lb. CO2/MBtu
Natural gas	117
LPG	141
Distillate oil	161
Pellet Wood	1.613
Cord Wood	1.613

Table 34. contains the state level emissions factors for electricity.

Table 34. State Level Electricity Carbon Emissions Factors (as CO₂)

Notes on Tables 34:

• Used data from eGRID (Emissions & Generation Resource Integrated Database), which contains emissions and resource mix data for virtually every power plant and company that generates electricity in the United States. eGrid version is eGrid 9th ed. year 2010 Data.    
• The state-specific level emission factors updated to eGRID 9th edition, year 2010 data. The state specific emissions only used for HI and AK, as before included because used in past version.   
• States are mapped to the eGrid sub-regions by visual inspection and judgment.   
• There are 3 difficult cases in which the state contains (entirely, not just overlapping) more than one region so mapping is particularly unsatisfactory.   
• Hawaii- there are two regions, Hawaii misc and Oahu. The emission factors are fairly close, and because it seems unlikely that Hawaii imports much electricity the state emission factor was used rather than chosing a region
• Alaska- there are two regions Alaska misc covers most of the area, the other proably includes Anchorage, so may represent more people. The two regions have very different emission rates, so used the state emission factor here also.
• NY- there are 3 regions, Upstate, City and Long Island. Upstate and City are fairly similar (<15% difference), but Long Island much (2.5X) higher. Because is represents most of the area, used the emission rate for upstate.