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 34 contains the state level emissions factors for electricity from EPA eGRID 2019 .

Table 33. National Carbon Emission Factors (as CO₂) from Residential Fuel Combustion

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