How much air the space needs
The figure to compare is airflow in cubic metres an hour. As a rough guide, around 400 to 3,000 suits drying, small rooms and pushing air along a hose, 3,000 to 6,500 suits site and workshop ventilation, and 10,000 to over 45,000 suits warehouses and factory floors. To size one, multiply the floor area by the ceiling height, then by how many times an hour you want the air changed.
Open floor or ducted run
Open floor and drum fans move huge volumes on modest power, so they suit circulating air through a big building and cooling workers with a strong breeze, but most lose much of their airflow when pushed through ducting. Radial, conveying and ducted extractor fans build more pressure, quoted in pascals, so they keep air moving through a long duct and into or out of a confined space. Whenever ducting is involved, compare the pressure figure as well as the airflow.
Site power, upkeep and confined spaces
Most plug into a 230 volt socket, several come in 110 volt versions for building sites, and some of the largest need a 400 volt three phase supply, which a qualified electrician has to install. Upkeep is mainly keeping guards and blades free of dust and checking cables, and power use rises with size, from well under a kilowatt for small fans to several kilowatts for the largest. Ventilating a confined space is one part of a safe system of work, alongside testing the air, never a substitute for it.
