Increase in total heat output of panel radiators could play an important role in domestic energy saving, where convectors (convection fins) play a key role. Hence, it is important to obtain the best possible design of convectors, in order to increase the heat output of panel radiators. In this sense, a numerical study has been performed to show the effects of different geometrical dimensions of convectors on the heat transfer used in domestic panel radiators, to obtain the highest possible total heat output. Firstly, simulation data were verified by analytical results, and afterwards, parametric studies were performed for a single convector mounted on a constant temperature wall, and the natural convective heat transfer has been modelled. The effects of convector height, convector sheet thickness, convector trapezoidal height, distance between opposing convectors, convector tip width, vertical location of convector and cut-off ratio have been considered. The results showed that the heat transfer increases with the increase in convector thickness and height. However, the consumed sheet metal material amount increases as well. From a manufacturing point of view, this should be considered at the same time. On the other hand, with the increase in trapezoidal height, the heat transfer increases, and above a certain value the heat transfer decreases. The heat transfer increases with the distance of opposing convectors and becomes almost constant above a certain value. The results of the present study could guide in the change of the internal design of panel radiators with convectors, in order to increase the heat transfer and reduce material costs.