If the exterior wall is 5 feet from the fireplace can I still install the air kit?
Yes, however the outside air kit ducting would have to be extended for your purposes, as the standard duct length would not be sufficient. Aluminum dryer ducting is able to be used to extend the air kit if needed.
This item is designed to draw outside air in through an exterior wall and supply it to your appliance. The flex venting will pass through the wall to the appliance. Only the termination would be located outside.