This study explores the influence of inlet subcooling and two-phase inlet on flow boiling heat transfer and critical heat flux in a horizontal 2.5-mm wide by 5-mm high rectangular channel for top wall heating, bottom wall heating and double-sided heating configurations using FC-72 as working fluid. High-speed video imaging is used to identify dominant interfacial characteristics for different combinations of inlet conditions and heating configurations. Three inlet conditions are compared: highly subcooled liquid, slightly subcooled liquid, and saturated two-phase mixture for mass velocities between 205.1 and 3211.6 kg/m(2)s. Gravity is shown having a dominant influence on interfacial behavior at low mass velocities below 400 kg/m(2) s, while inertia dwarfs gravity effects at high mass velocities around 1600 kg/m(2) s. Overall, CHF increases monotonically with increasing inlet subcooling. CHF variation between the three heating configurations is large for low mass velocities and diminishes for high mass velocities. A dimensionless parameter, heat utility ratio, is shown to be an effective means for assessing the influence of subcooling on CHF. (C) 2015 Elsevier Ltd. All rights reserved.