A dual-fuel range that uses a gas cooktop and electric oven is on the whole less efficient than a pure gas range. Electric ovens are less efficient overall than gas ovens, so the electric oven portion of a dual-fuel range costs more to run than a gas range oven.
A dual-fuel range uses the least efficient combination of gas and electric cooking possible. While gas ovens are more efficient in terms of energy use, gas range burners only convert 55 percent of the energy in gas into usable heat for cooking, versus 65 percent for traditional electric cooking elements. Induction elements are even more energy efficient, with up to 90 percent of the energy in an induction element's input electricity going towards cooking.
The main advantage of a dual-fuel range over a gas oven is not in efficiency, but in the precise adjustments to temperature possible when using gas burners and electric ovens. High-end electric ovens can consistently keep internal temperatures within 10 degrees Fahrenheit of the set temperature, while gas ovens can struggle to maintain consistent cooking temperatures. Conversely, gas burners are much more adjustable than almost any electric element, so it is much easier to cook food exactly as desired on a gas range.