Secondary school students have called for the measure to be lifted, complaining of the cold making it difficult to concentrate in class.
Officials recommend windows are open before and after rooms are in use to prevent the spread of Covid.
Pat McKenna, principal of Pobalscoil Neasain in Baldoyle, says the situation has been difficult:
"Rooms are at pretty much full capacity. So therefore you're monitoring your co2 levels you're trying to balance that through put of air is balanced by the comfort level for the students. And that's not easy because that can fluctuate throughout the day. It depends on the number of students in the room, etc. So that has been a challenging thing for teachers and for students. In terms of their particularly their comfort levels."