This study analyses heat consumption for heating domestic water in large hospital facilities with over 600 hospital beds. The tests were carried out in 2 hospitals: the 715-bed University Hospital in Bydgoszcz and the 690-bed Provincial Hospital. The tests were performed over a period of 4 years: 20052008 for the first hospital and 2003-2006 for the second. The aim of this study is to analyse the variations and seasonal changes in the heat consumed to produce domestic hot water during the specified time periods. The results of this study show the yearly, monthly, daily, and hourly consumption of heat for domestic hot water. Particular emphasis is placed on the daily and hourly heat-consumption irregularity coefficients for domestic hot water. The results of this study may be used, for example, to predict heat consumption when designing new hospital facilities with 500-800 beds, to determine the heating power of the heat source and individual centres. Data on the constant and low-temperature heat consumption for domestic hot water throughout the whole year are particularly useful, as these data may be used to analyse existing large hospitals that are seeking alternative solutions (such as renewable energy or energy recycling) to reduce fossil fuel consumption. (C) 2010 Elsevier B.V. All rights reserved.