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Emissions from home energy use
ElectricityThe CO2 emission factor used is 0.309 kge / kWh, taken from BEIS (2018) [1] . This includes an allowance for the 7.8% of transmission/distribution losses on the national grid [1]. There is a more recent (2019) document [2] with a smaller factor of 0.277 kge / kWh. However, the 2018 value is preferred here because much of the reduction is due to the switch from burning coal to burning wood pellets, with the burning of wood pellet being treated as zero CO2 emission. Whether burning wood can be considered zero carbon is highly controversial [3].The average electricity consumption is 4,800 kWh per household [4] . A smaller than average household is taken arbitrarily to be 3,000 kWh (i.e. roughly twothirds of the average), and a larger than average household to be 7,000 kWh (i.e. roughly 50% more). A value of 2000 kWh per person per year is used for student accommodation in a hall of residence [5]. (Mark Linas [6] makes the following alternative suggestions: small house: 1,650 kWh; medium house: 3,300 kWh; and mansion: 5,000kWh.) Domestic electicity use (excluding heating) is made up of [7]:
'Green' electricity For selected "green" tariffs, we recommend a reduction of 25% in the CO2 emission factor  see "Green electricity" at https://www.carbonindependent.org/16.html Natural gasMost modern gas meters measure gas in cubic metres. The energy contained in gas is measured in kilowatthours (abbreviated to kWh) and for natural gas, this is 11.2 kWh per cubic metre.Older gas meters measure gas in hundreds of cubic feet  100 cubic feet equal 2.83 cubic metres. So the energy contained in gas measured by an older gas meter is 31.7 kWh per 100 cubic feet. The CO2 generated by burning natural gas is 0.185 kg / kWh [8] . In 2006, the total UK gas supplied was 1,047,000 GWh, but of this 79,400 GWh was 'Energy industry use' and 12,000 GWh was 'Losses' (see source [4] Table 4.1). These total inefficiencies were 91,400 GWh, i.e. 8.7%, and so the CO2 emissions need to be adjusted by this amount from 0.185 to 0.203 kg / kWh. The average UK annual gas consumption is 16,000 kWh per household [4], but per meter is 18,000 kWh [4] (a larger amount as not every household has a supply of natural gas). A smaller than average household is taken arbitrarily to be 12,000 kWh (twothirds of the average gas meter), and a larger than average household to be 27,000 kWh (50% more). A value of 5000 kWh per person per year is used for student accommodation in a hall of residence [5]. (Mark Linas [6] makes the following alternative suggestions: small house: 10,000 kWh; medium house: 20,500 kWh; and mansion: 28,000kWh.) Heating oilThe factor assumed is 2.96 kg CO2 per litre of oil.The CO2 emissions from the burning of oil (from source [7]) is 2.52 kg CO2 per litre (which is equivalent to 3.15 kg CO2 per kg, and 0.245 kg per kWh) [7]. But this needs to be adjusted for the fossil fuel used in the extraction of oil and in refinery inefficiency, which together gives an inefficiency of 15% (see car sources page), giving a figure of 2.96 kg CO2 per litre. Other sources give 2.5 kg/litre (NEF) [9], and 3.0 kg/litre [6]. CoalThe emission factor assumed is 3.26 kg CO2 per kg of coal. This is the value given by DEFRA (2012) [10]WoodThe emission factor assumed is 0.10 kg CO2 per kg of wood. This is based on the values given by DEFRA (2012) [10]. The direct emission are taken as zero, since the CO2 released is just what was taken up when the trees grew, but there is a small level of emissions due to transport and other overheads . Whether it is correct to count wood as zero emission is a contentious issue according to Biofuelwatch [3].Bottled gasThe emission factor assumed is 3.68 kg CO2 per kg of bottled gas. This is based on the values given by DEFRA (2012) [10].References
First published: 2007 Last updated: 5 Mar 2020 