- A high-volume low-speed (HVLS) fan is a type of mechanical fan used in commercial and industrial settings. They have diameters between 10 to 24 ft (3 to 7.3m). HVLS fans move very slowly and can move large amounts of air at low rotational speed - hence the name 'high volume, low speed. - HVLS fans are considered the most effective of these types of fans, since they effectively circulate the air in a room to create a draft throughout the room. - They are often used to supplement HVAC systems, as they provide a stronger cooling effect while helping to maintain a constant temperature and humidity. - When used with air conditioning, they allow the raising of the thermostat setting about 4°F (2.2°C) with no reduction in comfort.