An experimental investigation has been undertaken to determine the effect of heated surface height on forced convective boiling. An inert fluorocarbon, FC-72 (3M Industrial Chemical Products Division) is circulated through a vertical rectangular channel at velocities of 1-4 m/s and subcoolings of 20 and 35 C. Results for five surface heights, as measured relative to the flow channel wall, were obtained. These were 0.127-mm recessed, 0.229-, 0.457-, and 0.635-mm protruded and flush with the flow channel wall. A reduction in critical heat flux (CHF) occurred at low velocities, while an increase occurred at higher velocities for the protruded cases. A reduction of CHF occurred at all velocities for the recessed condition. Additional results in the velocity range of 5-7 m/s are presented for the flush condition. This data shows that for velocities greater than 4 m/s, CHF becomes weakly dependent on the Weber number. Weak dependence on Weber number also implies a direct proportionality to velocity and a weak dependence on heated length.