You would have to do some pretty intensive record keeping to come up with a proper answer to this. The thing about an oven, in particular, is that it will be thermostatically controlled, so won't be using energy all the time, even when it is in use. This is true of both gas and electric ovens, and the better insulated they are (ie, the less heat you can feel from outside the oven) and the less you open the door, the less energy they will consume.Millymollymandy wrote:Trouble is it is really hard to know whether it is a false economy or not. How can you calculate how much your electric kettle/electric oven actually uses?
In theory, nearly all the electricity used to boil a kettle of water is applied directly to the water, with very little going to waste (the element is surrounded by water, so the water is the first thing to absorb the heat). On the other hand, when you put a kettle on a gas ring, you are also heating some of the cooker, and lots of air, so a good deal of the heat from the flame is lost, and not heating the water at all.
But, you should also consider how wasteful it is to generate electricity in the first place. In nuclear France, this is going to be a whole issue quite appart from simple efficiency. In the UK and elsewhere, much of the electricity used to boil an electric kettle started off as gas anyway.
Unless you actually have a gas flow meter connected to the bottle, it's going to be hard to tell how much gas is used in boiling a kettle, or powering the oven, so a real comparison will be difficult. ATM, it is generally cheaper to use gas (even bottled gas), but that is not the same as saying it is more efficient (ie, that you are using less of the world's resouces). And as gas prices rise, who knows what will be the case in the future.