The energy consumption of a building depends on the thermal demand and on the mean performance of the system. Apart from passive solar indoor climate control techniques, it is also possible to reduce conventional energy consumption of a building, even bringing it close to zero by installing solar heating. Hence, better knowledge of these techniques and of how they can be implemented in a simple but effective way will further progress towards more energy efficient buildings. The present work describes a straightforward procedure - applicable in any part of the world - to estimate the climate variables, to compare the efficiencies of solar heat collectors, and to size certain installations for domestic hot water, radiant flooring, or heating of buildings. The values of the climate variables - the monthly means of the daily values of solar radiation, maximum and minimum temperatures, and number of hours of sun - are determined from data available in the FAO's CLIMWAT database. Even though the calculation process uses approximate values for the variables involved rather than taking their dynamic evolution into account, it is fairly precise, giving results that are comparable to other more sophisticated and less easy to handle procedures such as the worldwide known f-CHART, TRNSYS, ISOFOTON and CENSOLAR computation programs. The predictive validity of the procedure has also been tested by comparing the results with those obtained experimentally via a solar heat collector installed on the roof of a building in the city of Badajoz. We believe that the procedure together with the computation program, will be of great use to builders and architects, since it allows a solar installation to be rapidly sized for applications in active solar heating schemes for building design. (C) 2006 Elsevier B.V. All rights reserved.