The energy costs of a convection oven depend upon its uses as well as the type of energy used. For baking, gas ovens as well as their stove-top counterparts heat up much more quickly than those powered by electric energy, which rely upon coils that take time to reach appropriate temperatures. In addition, the cost of natural gas is typically much lower than that of electric on a per-unit basis. On the other hand, electric energy creates less residual heat, so higher per-unit costs may not necessarily mean a greater cost in total consumption.
Efficiency and Usability
Electric ovens are typically more precise in terms of their responsiveness to temperature controls. The ability to better regulate temperature allows the owner to waste less heat and to lessen his chances of over or under-cooking many foods. In addition, the residual heat created by gas ovens may call for high expenses generated from the constant use of a cooling/ventilation system; this particular factor depends upon the gas oven model--some models are better insulated and effectively minimize these costs.
Gas ovens tend to be less safe in that it is more difficult to control their temperatures; however, electric ovens stay hot for a longer period of time and may pose a threat to children or pets for many minutes after use. Generally speaking, though, electric ovens require less supervision, and there is no possibility of explosions as with gas ovens--a scenario that, although unlikely, could be fatal.
Installation and Maintenance
Installation and maintenance in electric convection ovens is not only easier and more accessible for technicians, but maintenance costs are ultimately much lower--as electric-powered convection ovens tend to run longer and have less problems throughout their lifetime.
While general information is available regarding gas and electric comparisons, performance and efficiency may ultimately have more to do with the specific model of convection oven than with the type of energy source under consideration.