Municipal waste incinerators in the EU can replace other fuels to produce energy. A study looked at how efficient these incinerators are in terms of energy use. Results showed that incinerators producing electricity alone don't replace any primary energy. But those producing both electricity and heat can replace a significant amount of primary energy. Larger incinerators are more efficient than smaller ones. Surprisingly, some landfills are more energy-efficient than small incinerators. These findings challenge the current energy efficiency classification of incinerators.