Three-dimensional numerical simulations were performed of condensing R134a flows in a smooth horizontal pipe with an inner diameter of 8.4 mm and a length of 1.5 m, and validated against experimental results. A constant mass flux of 100 kg m⁻² s⁻¹ was considered and the influence of vapour qualities (0.25 to 0.75) and saturation temperatures (30 °C and 40 °C) on the resulting flow regimes and heat transfer characteristics of these flows were investigated. The volume-of-fluid (VOF) method was employed in the numerical framework to track and reconstruct the interface between the liquid and vapour phases. The simulations, given the imposed flow conditions, produced stratified wavy flow which are in agreement with the expected flow pattern based on the El Hajal flow pattern map. The heat transfer coefficient in the numerically simulated flows were found to be in good agreement (within 1.3%) with corresponding experimentally-measured values. From the simulations, the liquid-phase height at the bottom of the pipe was observed to be smaller with increasing vapour quality, which results in an increase in the heat transfer coefficient. A thicker film thickness and lower heat transfer coefficient were noted at the higher saturation temperature.