Martinopoulos, Georgios; Papakostas, Konstantinos T.; Papadopoulos, Agis M. (July 2018). "A comparative review of heating systems in EU countries, based on efficiency and fuel cost". Renewable and Sustainable Energy Reviews. 90: 687–699. Bibcode:2018RSERv..90..687M. doi:10.1016/j.rser.2018.03.060.
Martinopoulos, Georgios; Papakostas, Konstantinos T.; Papadopoulos, Agis M. (July 2018). "A comparative review of heating systems in EU countries, based on efficiency and fuel cost". Renewable and Sustainable Energy Reviews. 90: 687–699. Bibcode:2018RSERv..90..687M. doi:10.1016/j.rser.2018.03.060.