Commission Regulation (EU) 2015/1189 of 28 April 2015 implementing Directive 2009/125/EC of the European Parliament and of the Council with regard to ecodesign requirements for solid fuel boilers presents the way to determine the seasonal space heating energy efficiency (SSHEE). The value of SSHEE depends on (inter alia) a negative contribution to the SSHEE by auxiliary electricity consumption. In the current work, the analysis of sensitivity of electricity consumption measurement on SSHEE has been presented. The experimental and analytical investigations of 69 boilers (52 coal-fired and 17 biomass-fired) was carried out in the range of power of 2.8–517 kW and thermal efficiency of 83.1–96.3%. It was proved that the available relative uncertainty of electricity consumption gauge (i.e. < 5%, guaranteed by suppliers) is acceptable to obtain accurate analysis. The electricity consumption in automatic solid fuels-fired boilers was experimentally determined for 69 units and the electricity consumption demand was less than 1% of nominal thermal power. This research was investigated under the project “Utrzymanie potencjału badawczego Centrum Badań Technologicznych” (IChPW no. 11.20.011), financed by the Ministry of Science and Higher Education, Republic of Poland.