An electric kettle is ~90% efficient, the rest is lost to the surroundings but the electricity generation (assuming gas) is ~60% so the entire process, gas to h

An electric kettle is ~90% efficient, the rest is lost to the surroundings but the electricity generation (assuming gas) is ~60% so the entire process, gas to hot water is ~60% and most of the waste you don't get the benefit of. And gas stove kettle is ~40% efficient but you get the other 60% back as heat in the surroundings, so the entire process is ~100% efficient. Assuming you need that waste heat of course. In the summer that 60% inefficiency really is an inefficiency.