What's the difference between a 4-blade and 5-blade fan?
That's a very good question. The main difference between a four and five-blade ceiling fan is primarily one of aesthetics and personal taste. However, the laws of physics do dictate a slight difference in performance between ceiling fans
with different numbers of blades.
Noise vs. Efficiency
As a rule, as the number of blades goes up, the fan tends to be quieter while it circulates less air. Additional blades increase the drag coefficient on a ceiling fan's motor and will, therefore, slow it down. This is one of the reasons why industrial fans (like wind turbines) usually only have two or three blades; they can go faster and move more air, and noise isn't so much of a concern for them.
A Balanced Ceiling Fan
These days, many ceiling fans
designed for the home come standard with four or five blades. Beyond having a pleasing symmetrical aspect, it's at the four-blade and five-blade level that the ideal balance seems to be achieved between the amount of air circulated and amount of tolerable ambient noise.
The Bottom Line
That being said, you are unlikely to notice any major difference in job performance between fans with fewer or more blades. These days, advancements in overall residential ceiling fan design, balance, and low-drag blade shapes and pitch ensure that ceiling fans with a non-standard number of blades are still able to do their job quite well.
Don't be afraid to mix it up. Regardless of whether it comes with two blades, four or six, you can install your ceiling fan of choice with total confidence in its efficiency.