The article deals with the problems of determining heat power in a heating system taking into consideration solar radiation surpluses as well as increase in heat demand resulting from a higher wind speed. It is relatively simple to calculate these surpluses and heat losses for a single building. However, it is much harder or sometimes impossible, to estimate heat losses and surpluses related to solar radiation and wind influence for building complexes heated by a heating system. Results of the empirical research of these processes allow to property, and in advance, steer the work of the heat source or sources feeding the heating system. (C) 2008 Elsevier B.V. All rights reserved.