Different methods may be used for measurement of very high solar irradiance on large areas, all of them are based on one or several heat flux sensors. The most common gages used for this purpose are the Gardon type, which are usually calibrated using a black body at a certain temperature as the radiant source. An alternative way to calibrate these sensors based on a thermal balance is presented in this article. The agreement between both methodologies confirms the validity of the black body calibration procedure and the potential of the calorimetry to calibrate heat flux sensors. However, with the proposed method, the uncertainty in estimating the calibration constant of these sensors is reduced from 3% to less than 2%. This procedure calibrates these sensors to measure properly under concentrated solar radiation. (c) 2006 Elsevier Ltd. All rights reserved.