A study on mixed convection heat transfer in a laminar, fully developed, vertical channel is performed for three different cases: i) clear fluid channel ii) saturated porous medium filled channel iii) partially porous medium filled channel. For the all analyzed cases, motion and heat transfer equations are solved both analytically and numerically. The governing equations are presented both in dimensional and dimensionless forms. The dimensional forms of the governing equations are solved by numerical method while dimensionless equations are solved analytically. The dimensional results, obtained by numerical method, are converted into dimensionless values and compared with dimensionless results of analytical solutions. Good agreement between analytical and numerical results is observed. Based on the obtained results, velocity and temperature profiles are plotted for different values of Gr/Re, Da and porous layer thickness. A detailed discussion is performed on the obtained results. Moreover, heatline functions are obtained and plotted for different values of Gr/Re, Da and Peclet number. It is found that flow reversals in the channel highly depends on Gr/Re value and flow reversals occurs in the channel if Gr/Re exceeds threshold value. It is also found that for low Peclet numbers (i.e., Pe = 0.01), the path of heat flow is independent of Gr/Re and Darcy number. However, for high Peclet numbers (i.e., Pe = 5), the ratio of Gr/Re, Darcy number and thermal conductivity ratio influence heatline patterns, considerably.