Worth aged buildings represent among the existing buildings a special case when it comes to their energy refurbishment. Unfortunately, the available technologies for building components characterized by high level of thermal performances show, not rarely, a limited compatibility with the architectural integrity of the building. In other words, the so-called Best Available Technologies, which are effectively adopted to optimize the building energy performances, in case of buildings to which a certain artistic, historic and/or architectural merit is recognized, i.e. heritage houses, might determine such kind of conflicts. This situation may lead to the selection of “non-invasive” but less performing building and plant elements. To check the effectiveness of these less performing technologies, we investigated the energy performance of two different refurbishment configurations of the building envelope of a heritage house: a “Best Available Technology” scenario, in which interventions assumed consist of using the Best Available Technology for energy saving; and an “Allowed Best Technology” scenario, in which interventions assumed consist of using technologies that, although not the best available ones, are anyway “allowable” according to the cultural heritage preservation requisites and rules. A cost-based comparison between these two configurations was also made. Results of this comparative analysis are reported here.