Power Size EN3 is the minimum closer strength required for any fire doors that must be fitted with an automatic closing device, as per recommendations in BS EN 1154.
EN1 and EN2 are defined in the Standard, but are only recommended for use on non-fire doors and are not actually suitable for use on fire doors. This is because fire door leaves are denser and heavier than non-fire doors, they are fitted with seals around the door edges which may cause resistance when closing, and it is critical that they are fully closed to prevent the spread of fire and smoke. Fire door closers therefore need to apply more force to fully close the door.
BS EN 1154 is the harmonised British-European Standard which covers performance and test methodology for door-closing devices, not limited to those intended for use on fire doors. EN Power Sizes are a classification system for door closers, where each power size corresponds to a range of door widths and weights that the closer is suitable for to ensure the door is fully closed. They range from EN1 (maximum door leaf width of 750mm and weight of 20kg) to EN7 (maximum width of 1600mm and weight of 160kg). Power Size EN3 supports doors up to 950mm wide and weighing up to 60kg.