An experimental investigation on two-phase flow boiling heat transfer with refrigerants of R-22, R-134a, R-410A, C3H8 and CO2 in horizontal circular small tubes is presented. The experimental data were obtained over a heat flux range of 5-40 kW m(-2), mass flux range of 50-600 kg m(-2) s(-1), saturation temperature range of 0-15 degrees C, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 0.5, 1.5 and 3.0 mm, and lengths of 330. 1000, 1500, 2000 and 3000 mm. The experimental data were mapped on Wang et al. (1997) [5] and Wojtan et al. (2005) [6] flow pattern maps. The effects of mass flux, heat flux, saturation temperature and inner tube diameter on the heat transfer coefficient are reported. The experimental heat transfer coefficients were compared with some existing correlations. A new boiling heat transfer coefficient correlation that is based on a superposition model for refrigerants in small tubes is presented with 15.28% mean deviation and -0.48% average deviation. (C) 2011 Elsevier Ltd. All rights reserved.