Many economists and psychologists have studied the impact of nudges on households' pro-environmental behaviors. Interestingly, "private nudges'' can be imagined for companies. Yet, studies focusing on nudging employees' energy use are rare. The objective of our paper is to explore this issue with the help of a field experiment conducted at 47 French companies' sites. Using a difference-in-difference methodology, the effects of three nudges on employees' energy conservation are tested. The first nudge, "moral appeal'', stresses the responsible use of energy. The second one, "social comparison'', informs employees on the energy consumption of other firms participating in the experiment. Finally, the third nudge, "stickers'', alerts employees about good energy conservation practices. Our results stress the complementarity of these nudges. When implemented alone, the three nudges have no significant effects on energy consumption. However, when the moral appeal and social comparison nudges are combined with the stickers one, they become effective.