Once upon a time not so long ago a tortoise built himself a very low energy home. His energy use did indeed turn out to be very low but due to some strange accounting his full energy use was recorded on a list of very low energy buildings as two and a half times higher than his electricity meter had recorded.

The hare on the other hand was using fossil fuels and wood to supply most of his energy and as these didn’t carry the same multiplier his energy use looked pretty good too. This was despite the fact that his house was using just about two and a half times more energy than his neighbour the tortoise.

Until that was that oil, gas and wood all ran out or became prohibitively expensive. Now the hare had no choice but to convert his home to electricity as it was the only transmittable form of energy but he found that he now needed two and a half times as much as the tortoise who was still enjoying his low energy warm and cosy environment at a much lesser cost the his poorer, colder and sadder neighbour the hare.

It all depends whether the hare and tortoise are running a sprint or a marathon. Are fossil fuels going to run out and electricity generation be greened before the boiler wears out?

However, I think it's pretty clear that more insulation is better whatever happens.