Calculations of energy requirements for space heating in EPIQR are based on an existing computer programme, made according to the European standard EN 832:1998. The programme was originally a stand-alone programme with its own user interface. This has been stripped of and the source code re-compiled into a dynamic link library (DEL) controlled by EPIQR. The method is based on a monthly calculation of heat losses and usable heat gains for the building. For the calculation, the monthly mean values of the external temperature and solar radiation are applied, and the heat gain from lighting and appliances, as well as the heat-accumulating capacity of the building, are taken into consideration. In EPIQR, some input parameters have been fixed to ensure that the user only has to supply simple input data to carry out a heating requirement calculation. This paper describes the applied calculation technique and the assumptions made in EPIQR to carry out heating requirement calculations and how energy-saving retrofit is evaluated using the software. (C) 2000 Elsevier Science S.A. All rights reserved.