In the paper presented have been considerations regarding a model of boiling heat transfer in conventional and small diameter channels. Modified has been a model postulated earlier by Mikielewicz [J. Mikielewicz, Semi-empirical method of determining the heat transfer coefficient for subcooled saturated boiling in a channel, Int. J. Heat Transfer 17 (1973) 1129-1134] to incorporate the surface tension effects into the two-phase flow multiplier as well as the empirical correction influencing the nucleate boiling heat transfer term. The changes to the model under scrutiny were both of qualitative and quantitative character as the entirely new data bank of experimental data points has been collected to devise a new form of a semi-empirical model applicable both to conventional and small diameter channels. The fluids examined were: R141b, R134a, R113, R12 and R11 and the total number of considered experimental points, corresponding to small diameters. amounted to over 260. The range of considered tube diameters varied from 1 mm to 3 mm. The use of the model is very simple on account of its analytical form, which is its fundamental advantage. It is of general character, and its coefficients do not depend on the type of fluid. Comparisons with experimental data show good agreement. (c) 2007 Elsevier Ltd. All rights reserved.