How are carbon emissions savings calculated for gas boilers? October 14, 2021 By The Carbon Trust (The UK) is a valuable source of information on all things carbon. They provide a conversion factors guide to help you calculate your organisation’s carbon emissions – with guidance on how to convert energy use and carbon emissions into common units. Carbon Trust conversion factors. As gas is burnt to heat the water in a boiler carbon dioxide (CO2) is emitted into the atmosphere. These conversion factors state that for each kWh of gas used 0.1836 kgCO2 is released. Therefore 1 tonne of CO2 is emitted for every 5446 kWh Any reduction in gas consumption will reduce carbon emissions by the same amount.