Building’s energy performance is the results of materials and components performances. Concerning windows, the energy performance of these components depends on glass and frame heat transfer coefficients, on linear heat transfer coefficient due to spacer type and finally on frame installation. The entity of thermal losses due to the frame installation can be computed in term of linear thermal transmittance if calculated in accordance to EN ISO 10211. The analysis of thermal bridges between a wooden frame-window installed into two different kind of external walls has been carried out. Using THERM 5.2 the linear thermal transmittances have been calculated for three cases regarding position (external, internal, intermediate) and concerning insulation of hole perimeter (non insulated, insulated and with insulation over fixed frame). The entity of the frame installation in terms of thermal losses has been estimated in different climatic conditions. The frame position and the hole insulation can highly modify thermal losses.