I am currently doing a small home renovation project and there maybe a need to permanently close an air vent in the living room (there are two and I only need one as the room is small). I am thinking of taking out the grill and just installing a pre-cut cardboard in place of the air vent and shut it permanently.
Has anyone ever done something like this before? Any negative impact to the Heat/AC system as now there is less venting of the Heat/AC air than maybe what the system was designed for. There are still plenty of other air vents which will be left open though (more than 12).
It depends on your system's design...Ducts, AC unit size, etc. It will affect the static pressure for sure, but that may or may not be a good thing. If your AC unit was already oversized for your duct system, closing 1/12th of it off could be a bad thing. If it was perfectly sized, I doubt you'll see too much negative effect.
In any room you should have two vents...a supply, positive pressure...and a return, negative pressure. If the vent you are going to block off is the return, negative pressure, you may be creating problems.