In this study, new outdoor design conditions for space heating were determined for 78 locations within Turkey according to the format recommended by the American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc. (ASHRAE). Dry-bulb temperature corresponding to 99%, 99.6% and 97.5% annual cumulative frequency of occurrence, the mean and standard deviation of the annual minimum dry-bulb temperatures were obtained. These calculations used hourly data measured during at least 13 years. The current heating design conditions used in the calculation of space heating load in Turkey were analyzed based on their frequency levels. Comparison of the existing space heating design data with the data obtained in this study revealed that the current space heating design temperatures are generally stringent and provide total protection. (C) 2003 Elsevier Ltd. All rights reserved.