I have been amused at all the varied comments about P/C Covers and whether they should be on or off...
If I may, I would like to add a few additional comments.
Having been a Mainframe Data Center Manager for over 35 years I have seen all kinds of heat related problems on computers and other equipment.
As I see it, the covers serve 2 purposes.  First most electrical codes require them for safety. They keep untrained hands out of the machine. (Even trained hands sometimes forget the danger of electrical shock).
I once had to rush an IBM Tech to the hospital after he grabbed the wrong wire.   The second purpose is that the covers keep mice, rats, insects and other varmints out of our computers..
Perhaps the ideal cover solution is to cut large holes in the case sides and cover the holes with fine screen wire.  This would open up the P/C for air and still keep the critters out.

BOB..
                          

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