@WBYeats,
WB: Don't turn the fan to the lowest level when you don't use it. Turn it off.
jtt: Don't (just) leave the fan at the lowest level/setting when you aren't using it. Turn it (right) off.
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Original: When we want to say we make the fan produce the most powerless wind it is capable of giving, is that natural English?
After reading this, WB, I'm not completely sure what it is that you really want to say.