Numerical and experimental studies on laminar natural convection and radiation in a differentially heated cavity with/without triangular fins are presented. The square cavity is filled with air (Pr = 0.71). The top and bottom walls are adiabatic, while the active (hot) and cold walls are isothermal. Triangular conductive fins made of highly conductive material are placed on the heated and cooled vertical surfaces of a square cavity. The effects of pertinent parameters on fluid flow and heat transfer characteristics are studied. The governing differential equations, assuming laminar flow, are solved using the commercial software FLUENT. Experiments have been carried out for three different configurations viz square cavity without fins, square cavity with two fins on vertical walls and square cavity with continuous fins on vertical walls. Rayleigh number varies from 1.18 × 105 to 2.15 × 105 for the first experiment (square cavity without fins). The other two experiments with fins have been conducted for six different heat inputs. The numerical results have been validated against the experimental results obtained. It is concluded that the triangular fins on isothermal walls enhance the heat transfer in the cavity. Natural convection is influenced by wall surface emissivity. The square cavity with continuous fins is more effective than square cavity with two fins on vertical isothermal walls. © 2017, Springer-Verlag GmbH Germany.