This paper presents a study case to improve Energy Efficiency (EE) in a residential building under two considerations: introducing a new load to the system corresponding to the charging of Plug-in Electric Vehicles (PEV), and proposing an action plan based on the modernization of technological devices. Initially, the simulation of the electric system is performed to calculate variables such as voltage, power demand and losses for different PEV penetration scenarios. After that, EE indicators required to assess each scenario are evaluated and individual and collective plans are proposed. Finally, plans are evaluated with respect to their contribution on EE improvement.