This may be scrupulous, but I need to ask

[pianistclare]

Stealing is taking something which belongs to someone else, as opposed to taking something which does not belong to you. There is a subtle difference between the two concepts. Thus abandoned property which has no owner can not be stolen. There is only one problem for the OP - technically, it might be said that the company whose office it is owns the fan. But as for the people who left it there ten months ago? They abandoned it!

I doubt the owner of a company would purposely say:

Hey, let’s take this job, do the work, and then ABANDON our equipment there".
Come on .
Seriously?

SOMEONE from his office should have called the company and said "hey! you left some of your stuff! When are you coming for it? "
I guarantee they would have sent a worker out to retrieve it.
The worker who left it probably was penalized and had to buy one out of pocket to replace it. Think of other people FIRST.