In article ,
fred writes:

It's a guide, but it seems a bit unfair. eg all 'medium' sized ovens (35-65
litres) are grouped together so larger ones within the group which will need
more energy will look less 'efficient' than a smaller one in the same group.

Indeed. It will cost me more to cook one chicken drumstick in
a big oven than a small oven, so big ones are less efficient.

--
Andrew Gabriel