This paper investigated the interaction of two slot-burner buoyant turbulent diffusion flames at various burner pitches. Experiments were conducted by employing two identical slot burners (length: 142.5 mm; width: 2 mm) using propane as fuel at various fuel exit velocities. Results showed that with an increase in burner pitch, the interaction of the two flames made a transition from merging to non-merging, resulting in a complex non-monotonic evolution of flame height. An analytical model was developed to characterize the critical burner pitch for flame merging, which was found to be proportional to the free flame height, or have a 2/3 power law dependence on the fuel exit velocity. As a result of their interaction, the flame merging point height increased till the two flames separated with the increase in burner pitch. Meanwhile, the flame height was shown to first decrease, then increase and finally approach the free flame height with the increase in burner pitch. A scaling non-dimensional formula was finally proposed, based on the analysis of the change in air entrainment into the flame from the space between the two burners with burner pitch variation. This proposed formula was shown to well correlate the above transitions based on a newly defined non-dimensional heat release rate using an "effective" entrainment perimeter as a characteristic length, which includes the burner width and length as well as the additional flame base "extension" due to the change in burner pitch. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.