Airier Natura Pvt. Ltd. Manufactures Gravity Vent Ventilator. Airier Natura Pvt. Ltd. Is an ISO 9001-2000 awarded company that also manufactures a wide range of ventilators. Gravity Vent Ventilator is precision engineered. These are used to discharge exhaust ventilation and is great for cloths dryers, range hoods and others. It is available in various specifications such as 100mm, 125mm 150mm sizes.