> since gas stoves are less efficient and much worse for the environment than a kettle.
It is not obvious at all and requires calculations.
When you use electric kettle you use energy which was obtained mostly from coal and gas (60% of it in the US) and efficiency of the conversion is less than about 40% on average (limited by efficiency of a steam turbine). Then about 8% of this power is lost during transportation/distribution.
When gas is burned in a gas stove 100% of its energy converted to heat. The only problem - some fraction of this energy heats a room instead of a kettle. But it is not bad if you had to heat room anyway (where I live 8-10 months out of 12 I'd prefer indoor temperature to be higher then it is).
I expect this loss to be smaller than 50%, but I've not found credible numbers for this.
Efficiency for an oven may be low because it measurably heats a kitchen, but ovens is another story.
