Ball bearings "220V Cooling Fan" than the noise oil-bearing, the price is relatively expensive, but more reliable, universal service life longer than oil bearing, but some fan manufacturers in order to save costs, originally double ball bearing in private only installed a ball in "220V Cooling Fan" which, as the case without the knowledge of the customer, sell at high prices. Second, look at the ventilation rate, some of the cooling fan buyers always thought that the greater the cooling fins better, In fact, this is a misconception, "220V Cooling Fan" has the advantage of long blades, heat dissipation area, so the larger the gas flow. However, if designed properly, a big fan of cooling capacity may not be as good a small fan.