G960 Telescopic Underfloor Ventilator - Box of 20 The G960 provides 6,600mm2 airflow. Description The G960 Telescopic Underfloor Void Ventilator is designed to provide a clear airflow passage to the void underneath a suspended floor. The telescopic feature enables the ventilator to adjust vertically between three and five brick courses. The right airflow can be achieved when the ventilator is used with a Manthorpe G930 Airbrick. The aperture can also accept a standard clay airbrick, although the airflow is reduced. The G961 Vertical Extension Sleeve has been designed for use with the Manthorpe Telescopic Underfloor Ventilator (G960). Each extension sleeve allows the vent to reach a further two brick courses vertically. The sleeve can also be fitted to the base of the G960 to provide horizontal extension through larger cavities.