The education minister says teachers should open windows "at a lower level" if their classrooms are cold.
Ventilation requirements for pandemic safety have seen some room temperatures dip below seven degrees Celsius this week.
Health and safety rules require teaching to be suspended at 16 degrees.
Teachers' unions have criticised a lack of progress on acquiring air filtration systems for classrooms.
Minister Minister Norma Foley says going straight to technology, like HEPA filters, is not the answer.