Since the beginning of this century, according to EPBD Directive, Italian legislation has been focusing on existing buildings’ retrofit, as they represent a large part of the national building stock. In this context, the most difficult challenge is preserving heritage and obtaining energy saving at the same time, which is the aim of the European Standard EN 16883 published in 2017. Currently there are few energy efficiency actions that can be applied to improve the energy performance of these buildings, due to the strict regulation on ‘protected status’. The case study presented in this paper gives an overview of refurbishment solutions that can get around Italian legislation for one of the oldest heritage buildings in Padova. The building complex that can be seen nowadays is the result of the grouping of several surrounding buildings, renaissance palaces and medieval towers. Energy simulations have been implemented using EnergyPlus software. The thermal behaviour of the building has been investigated considering the peculiarities of the envelope and real weather data. Internal loads and generation system schedules have been estimated based on the information obtained from the system monitoring the energy consumption. Envelope and system retrofit have been considered.