The manuscript reports the experimental study results dealing with the ammonia two-phase flow pattern observations in the transparent horizontal tube of ID 7.5 mm with a saturation temperature of 15 to 65°C, mass velocity of 50 to 160 kg·m−2s−1 and vapour quality of 0.1 to 0.8. Stratified-wavy, annular-wave and annular smooth patterns have been identified based on analyses of camera images. The annular-wavy pattern was not distinguished in the previous ammonia studies at low saturation temperatures (Lima et al., 2009; Gao et al., 2021). Transitions between stratified-wavy and annular-wavy and between annular-wavy and smooth annular patterns occur at constant interfacial vapour momentum flux. This observation aligns with Hewitt and Roberts's (1969) suggestions for vertical steam-water flows. It does not match the existing iterations of Taitel and Dukler's (1976) map, which accurately predicts the transition of HFC fluids and partly the low-temperature ammonia tests. Implementing newly developed transitions between the two-phase ammonia flow patterns in the horizontal tubes updated and validated the existing hydraulic and heat transfer correlations. The most significant among them is an update to the Müller-Steinhagen and Heck's (1986) model in predicting adequately the ammonia frictional pressure losses in the horizontal tube for the broad range of boundary conditions.