Oxygen consumption (OC) calorimetry and carbon dioxide generation (CDG) calorimetry are usual methods to determine the heat release rate (HRR) in bench-scale and large-scale fire tests. The paper emphasises on measuring problems associated with fires releasing large amounts of soot. Until now, the soot-related energy transfer was hardly ever taken into consideration in practical applications of HRR calculations. From standard CDG calorimetry, a generalised relationship is introduced in order to take into account the soot generation in the accurate determination of the heat release produced in sooty fires. The analysis of the significance of this correction factor is discussed by theoretical consideration as well as from results of lab-scale experiments recently carried out on chemicals by means of the INERIS fire calorimeter.