I agree with the advice to contact the manufacturer and find out what
temperature range they specify for the freezer. While colder
temperatures will increase the efficiency of the condenser in getting
rid of the heat removed from the food, the oil in the compressor is
going to get more viscous with colder temperatures and may not lubricate
the moving parts in the compressor sufficiently.
Chest freezers are inherently more efficient than upright freezers
because cold air is denser than warm air. So, when you open a chest
freezer, the cold air remains inside as Derby Dad says.
Never ever never buy a used chest freezer if it's been turned off.
That's because chest freezers are built differently than refrigerators.
In a chest type freezer the evaporator coils line the inside of the
freezer side walls and the condenser coils line the outsides of the
freezer side walls. That's why the walls of a chest freezer will feel
warm, just like the condenser coils on the back of a fridge when it's
running. Because chest freezers don't have a automatic defrost like
fridges, over the course of several years, frost will accumulate on the
evaporator coils of the freezer. This space is sealed off and so you
don't get the kind of frost accumulation that you get on a manual
defrost fridge, but it will accumulate with time.
The problem is is that space is sealed off. So, if you turn off or
unplug the freezer, that frost melts and forms a puddle at the bottom of
the freezer. That water won't do any harm at all to the aluminum
evaporator coils on the inside of the freezer walls, but in time it will
cause corrosion of the STEEL condensor coils on the outside of the
freezer walls. That corrosion will make the steel rough, and that
results in what engineers call "stress raisers". If you have a notch in
a steel tube, and you continuously pressurize and depressurize that
tube, a crack will propogate from that notch because the stress on the
steel is highest at the notch because the wall thickness of the tubing
is smallest at the notch.
So, if you plan to sell an old freezer, put your ad in the paper, but
leave the freezer plugged in and running until it's sold. Otherwise,
knowledgable buyers won't want to buy it for fear it's not going to last