CFM (Cubic Feet per Minute) /CMM (Cubic Meters per Minute)
The amount of air a fan can move per minute (CFM / CMM) may be the most helpful of a fan's measurements. It actually measures a fan's ability to convert electricity to moving air. It measures the fan as a unit, not just the motor or the blades. Manufacturers that have measured their outdoor fans for CFM/CMM will gladly display this information.
If a manufacturer or retailer only gives you CFM or CMM, you may want to convert it to measurements you're more comfortable with:
1 cubic foot x 35.315 = 1 cubic meter
1 cubic meter x .0283 = 1 cubic foot
How much air flow do you need? We can pick up a general rule from the field of indoor cooling:
The amount of CFM needed to cool an area is about 3 to 4 times the area.
If you're holding an outdoor event for 10 people in a tent that's 10' x10' x10' (1,000 cubic feet), you'll need an outdoor fan with about 3,000 to 4,000 CFM.
In international measurements:
If you're holding an event for 10 people in a tent that's 3m x 3m x 3m (27 cubic meters) you'll need an outdoor fan with about 81 to 108 CMM.
The fan's blades can maximize the fan's air flow.
Beyond this general rule, the amount of air flow you'll need can best be determined by experimenting. A fan with variable speeds can be extremely helpful for this. In a small area like this tent filled with ten people, consider where you will put the fan. Is there room to put it in a corner? If the people will be standing a floor fan would work well.
If they will be sitting at a table you might want to consider a standing / pedestal fan or a table fan. If there is room, two smaller fans set up in different corners can be set on lower speeds and would likely be less nuisance to anyone sitting right next to them than one stronger fan might be.
ENERGY STAR fans have been reviewed by the U.S. Environmental Protection Agency and the U.S. Department of Energy. If a fan has earned this rating you can be assured it meets certain standards of energy efficiency regarding the reduction of greenhouse gas emissions. These fans are generally more energy efficient than other similar fans. More tests have been performed on energy star fans, and manufacturers are proud to display this information.
CFM/CMS ratings are listed for each speed on all Energy Star qualified outdoor fans. All these fans also state the motor's efficiency ratings and watts per CFM/CMM so you can compare them with fans that aren't measured for CFM/CMM.