Electric heating leads to higher CO₂ emissions than gas heating

The electrification of heating, while controversial, has significantly lower CO2 emission factors in France than gas heating, about 80 gCO2e/kWh according to the calculation methods recommended by the ADEME, compared to 180 to 210 gCO2e/kWh for gas.

Different calculation methods

The relevance of electrifying heating is regularly a subject of controversy, especially when developing regulations for the construction of new buildings. Several calculation methods coexist for determining the emission factor of heating: seasonal or monthly by use, incremental, marginal, etc. These methods do not necessarily provide the same information and do not meet the same objectives [1].

Today, ADEME recommends the use of the monthly method when drawing up carbon balances, and the incremental method for steering public policies. In a note published by ADEME in 2020, the agency estimated the emission factor of electric heating at 79 gCO₂e/kWh using the monthly method, i.e. an emission factor much lower than that of the kWh of gas burned in a boiler (from 180 gCO₂e/kWh to 210 gCO₂e/kWh) [1]. The incremental emission factor was quantified in a joint study by RTE (French electricity TSO) and ADEME (French Agency for Ecological Transition) at 80 gCO₂e/kWh. However, the study highlights the great uncertainty surrounding this figure due to the assumptions needed to calculate it [1].

A misuse of the marginal method

The high emission factors mentioned by some non-profits or in the press are based on a questionable application of the marginal method. The marginal method consists of calculating the emission factor from the last plant solicited on the network (i.e. the one with the highest variable costs). The error then consists in thinking that the marginal power plant when using electric heating is systematically a fossil fuel power station. In fact, a study by Carbone 4 for 2018-2019 highlights: "Contrary to popular belief, coal, gas, and fuel oil combined hardly reach 15% marginality.” It lands on an emission factor of 150 gCO₂e/kWh, far from the 500 gCO₂e/kWh sometimes mentioned [2]. It should also be noted that the use of this method is not recommended by ADEME to assess the climate impact of electric heating.