A numerical investigation of flow (Pr = 0.71) and temperature fields in a planar open loop thermosyphon is presented. The thermosyphon flow path is a modified ’U’ shape with an upper and lower inlet in the right channel of the ’U’. The flow was studied For different values of the governing parameters. These include the Rayleigh number (Ra), the lower inlet width and the wall thermal conductivity. Results indicate the temperature held is independent of the inlet configuration at large Rn. The how field is highly dependent on the lower inlet as recirculation at the outlet increases with inlet restrictions and boundary layer development at the heated wall. The wall thermal conductivity has large effects due to conduction resistance of the conducting walls and reduced natural convection effects.