All manufacturers have ceiling fans with 3, 4, 5 or even 6 blades. Why? The number one reasons is marketing and style, not efficiency. In my opinion the more blades a fan has, the more efficient it will be (to a point). A fan with five or six blades has blades that are in tune with the size of the motor turning the blades. In "tune" means the manufacturers have spent the R&D matching the pitch and length of the blade with the size of the motor.
Think about a Nascar race, often 3 or 4 cars can break away from the pack and get a good size lead on them but if the rest of the pack gets in line they can catch up and sometimes overtake the leaders and use less energy (fuel) doing so, the reason is vacuum. The movement of the air is more consistent over and through a 5 or 6 blade fan. Fans with more blades also are quieter because they can produce air movement with less energy, which cuts down on the chopping “helicopter” sound some fans make.
New DOE regulation (went into effect Jan. 09) require ceiling fan manufacturers to print in their catalog's and on the cartons some key information for the consumers. In addition to motor size, pitch and length of blades, Cubic feet per minute (CFM), electric used (watts) and air flow efficiency (CFM/Watt) have been added. Example: 6417 cfm, 70 watts, 91.6 cfm/watt. My opinion the "key" number is cfm/watt. Fans with integrated light kits is another subject for another time.
Another topic is whether or not you should operate the fan 24hrs or just when you are in the room. Think of it this way, a good fan recirculates the air in a room about every 5 to 10 minutes. All rooms have hot air next to the ceiling and cooler air next to the floor. Most thermostats are on the wall about 5 foot off the floor and your air conditioner cools the air on the floor up to the thermostats height, and does nothing for the air above that height. A ceiling fan running equalizes the temperature in the entire room top to bottom making your air conditioner run less time to keep your house cool, and when your air conditioner shuts down it can stay shut down longer because the fan continues to move cooler air off the floor past the thermostat.
My best advice is to buy your ceiling fans from a distributor that displays a variety of motor types and sizes so you can listen for any motor noise. Statewide Lighting's locations have a large selection to listen to and educated staff members to assist you make your decision (most box store do not). On the web we are at: http://statewidelighting.com or http://statewidelighting.com/shop/index.php?main_page=index&cPath=1
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