An Energy Life Cycle Inventory analysis was implemented on a 40 x 40 cm prototype electrochromic (EC) window routinely fabricated in the laboratory. The total production energy was found to be 2261 MJ 91% of which is allocated to the frame. about 7% to fabrication processes and the remaining 2% to the embodied energy of the raw materials. Various scenarios for EC operation in Greece were compared with respect to the induced heating - cooling loads and energy savings. When the EC window prototype is used instead of a single glass in heating dominated areas and large facades for a maximum expected lifetime of 25 years, the reduction in energy consumption can reach up to 54%, corresponding to 6388 MJ. Based on the conducted analysis, 0.9 years of operation of the prototype window are required to compensate the production energy of the plain EC device. This time period is extended to 8.9 years when the aluminum frame is taken into account, proving its extensive energy contribution. The total cost savings range from 228 to 569 euro/m(2) glass for 10 and 25 years of EC window operation respectively. (c) 2005 Elsevier B.V. All rights reserved.