Making a device more reduces the energy needed for each hour of use and reduces the cost of using it.
Some of the expected saving is therefore spent on using the device more, which is the effect.
Its existence is not in dispute and its size is, which is where the argument has for thirty years.
Direct is usually : a household with a cheaper-to-heat house heats it a little more.
Estimates cluster between ten and thirty per cent of the technical saving, which leaves most of it intact.
is harder to measure and is where the serious disagreement lies.
Money not spent on heating is spent on something else, and that something else required energy to produce.
A household that saves two hundred pounds and takes a flight has undone the saving several times over.
A household that saves the money has not, until the money is eventually spent by somebody.
Following the money to its end is an exercise with no natural stopping point.
Analysts therefore stop at a they choose, and the chosen determines the answer.
This is a respectable methodological difficulty and is routinely presented as an dispute.
The policy implication is smaller than either side claims.
Rebound does not make efficiency pointless; it makes efficiency on its own.
An efficiency measure paired with a price that rises as consumption falls captures most of the saving.
The pairing is unpopular because the second half is a tax and the first half is a gift.
Governments have consistently announced the first and postponed the second.
Thirty years later they are surprised that consumption has not fallen as the engineering predicted.