On 25/12/16 01:42, bert wrote:
The (/my) 'big question' is that if (say) the heater element get's
sufficiently hot as to start to boil the surrounding water, *does* the
heat get carried into the water as effectively as if it wasn't
boiling?

No Go watch a saucepan of water coming to the boil.

Yes, Go watch a saucepan of water coming to the boil.

With a lid on it.