Plug the holes with rokwool insulation or high temp caulk.
Direct vent fireplace cold air.
Proper research prior to installation is the key to simplifying the process.
A direct vent fireplace does a great job pulling 100 of its combustion air from the outside and dumping the exhaust back outside as well.
The good news is that direct vent gas fireplaces unlike vented gas logs generate heat efficiently when running.
This should stop the problem.
If the damper is not closed after use they can also let cold air into the house.
If you have not had the original installer over to look at the problem i would try that first.
If you have cold air coming out of the bottem vent there is no way that is coming from the combustion chamber and the combustion chamber is hooked up to the flue.
Direct vent fireplaces are a type of vented gas fireplace that does not use air from inside the home to operate.
We have several resources to help.
They feature a firebox sealed with tempered or ceramic glass and use a dual purpose vent that both vents exhaust to and pulls combustion air from the outdoors.
Where the controls are located there are usually gas line knockouts holes on the left and right side.
The sealed combustion chamber is always seperate from the box you frame in.
That absolute cheapist worst designed direct vent fireplaces should not have cold air coming out of them.
They can be vented both horizontally and vertically.
Cold air issues from the bottom of direct vent fireplace can usually be eliminated by checking underneath.
The bad news is if the fireplace installer does not take care to insulate the fireplace install correctly it will let in a great deal of cold air when dormant.
The chimney cap buying guide and the chimney pipe buying guide will help you find out what your options are and how.