This work analyses the capabilities and limitations of the regression method based in averages applied to the thermal performance analysis of real size building components tested in dynamic outdoors weather conditions. This study aims to distinguish which of the problems observed in these methods are specifically related to the regression average method such as the minimum integration period, and which are related to general aspects such as the minimum terms necessary in the energy balance equation which should also be solved in dynamic approaches. Integration periods from one to ten days have been considered. A noticeable improvement was observed as the integration period was increased from one to five days. Larger integration periods did not show significant improvements. The influence on the energy balance equation of global solar radiation, longwave radiation and wind speed has been analysed. Significant improvements have been observed including wind speed. To isolate and highlight the effects of the different analysed aspects from the effects of other assumptions about the test component and its boundaries, a well-known fairly simple opaque wall was analysed to find its U value. Experimental data recorded in the south east of Spain for a total of one year have been used. (C) 2012 Elsevier B.V. All rights reserved.