SF6 is a widely used insulating gas in the electric power industry due to its high dielectric strength. However, SF6 is classified as a greenhouse gas and has a very high global warming potential (GWP). Much research and development efforts have focused on finding alternatives to SF6 which have a lower GWP. An important requirement for an SF6 alternative is that it has similar heat transport properties to SF6, since one aspect of the design of high voltage equipment is the management of the heat dissipated from the flow of current. In the present paper, we compare the convective performances of SF6 and C5-flouroketone (C5-FK) and C4-flouronitrile (C4-FN) based gas mixtures. Mixtures of CO2, O2, and C5-FK/C4-FN have a GWP much smaller than that of SF6, a high dielectric strength, are not classified as toxic, and have good arc interruption properties. The numerical study is based on a semi-coupled computational electromagnetics (CEM) and computational fluid dynamics (CFD) analyses. The results of the numerical study are compared with experiments. There is a good agreement between the simulation results and the experiments. C5-FK and C4-FN based gas mixtures have good convective performance and are well-suited for application in circuit breakers. Thus, from the temperature-rise point of view, C5-FK and C4-FN based gas mixtures represent an alternative to the SF6 insulating gas traditionally used.