Buoyancy-driven free convection in a typical solar air heating system is investigated numerically using an indigenous code. Solar air heating (SAH) is reliable and economic for harnessing solar energy for heating/ ventilation of buildings. Design, as well as application of such system/devices, needs in-depth knowledge of its transport process. To address these issues, the present study explores the fundamentals of fluid flow and heat transfer process by modeling ‘H’ shape cavity packed with saturated porous media, heated from bottom protruded body and cooled at the sides of the top protruded body, respectively. Rests of the walls are insulated. Two different working mediums (air and copper–water nanofluid) are utilized for assessing the overall thermal behavior. Evolved flow physics is analyzed and visualized for a wide range of pertinent parameters like Rayleigh number (Ra = 103–106), Darcy number (Da = 10–7–10–3), porosity (ε = 0.1–1), the concentration of nanoparticles (ϕ = 0–4%), and heater aspect ratio (A = 0–2.5) for the clear domain as well as porous domain. All the results have been visualized by streamlines, isotherms, and heat lines. The heat transfer rate is influenced significantly by the different parameters. It is observed that usage of nanofluid ensures heightened heat transfer compared to air even in the presence of the porous medium. At higher Ra, an increasing trend of heat transfer is noted for aspect ratio from 0 to 1.0 for nanofluid (0–0.5 in case of air), beyond this heat transfer decreases, and then heat transfer increases.