Freezer efficiency: The temperature for a freezer should be
between minus 15C and minus 18C. Don’t allow ice to build up beyond 5mm
thickness on the walls of your fridge or freezer. Ice actually prevents
the flow of cool air, causing your fridge to work harder and consume
more energy than necessary. Ensure your fridge is not in direct sun, as
this also significantly increases its running cost as the unit needs to
work harder.
The Advertiser, 13/12/2005, p. 21
Source: Erisk – www.erisk.net