Simple knowledge of airflow would suggest that the number of blades on a whole house fan correlates to the greater amount of air that is pushed. This is actually a major misconception. More blades can help minutely but if more blades simply equaled more airflow then ceiling fans would have 10 blades, helicopters would have 20, and industrial fans would have 100.
In fact, some of the best ceiling fans on the market have just one blade. According to Fandiego, “With all things being equal, the ceiling fan with fewer blades will outperform (better airflow) the fan with more blades. It will actually move more air. Here’s why: With fewer blades, more air is actually circulated through the blades. In other words, air is more effectively circulated with fewer blades, because as the number of blades increases, more air has to be pushed around the blades. This makes the fan less efficient. Having fewer fan blades also decreases the weight on the ceiling fan motor so the motor can spin faster, circulating more air.”
So, for example, Quiet Cool’s fans have just three blades while other companies boast about improved airflow due to their superior number of blades when in fact air is actually pushed much more effectively with fewer blades. It is much more important to have a properly designed blade than a large amount of blades. This is why companies such as Quiet Cool focus less on the amount of blades they can fit in their whole house and attic fans and much more about how to get the blades they do have to work as effectively as possible.
More blades also increases the chances of a repair and can even increase the noise level. The increased risk of repairs is simply due to the unnecessary addition of parts. Doubling the amount of blades doubles their potential for malfunction. Like stated previously, more blades causes there to be more counter productive drag around the blades as air is forcibly pushed around each individual blade, the more blades, the the more air has to be moved in between the cracks.
While a whole house fan does not push or move air in exactly the same way, they are both dealing with CFM and the necessity of pushing the most air as conceivably possible. More blades simply does not accomplishment, even though the simple understanding of these machines would suggest so.