Free Web space and hosting from freehomepage.com
Search the Web

Large fans do not necessarily move much more air than small ones. The brand I got is available in 12", 14", and 20" sizes and move 2200, 2400, and 2600CFM respectively. So the 12 and 14 together are much more effective than a single 20". All three use the same motor and the larger blades just turn slower.

Using a thremo fan in conjunction with your regular fan might be a good idea, although the general consensus is that electric fans are most efficient as pushers not pullers. This will also negate some of the advantages of electric fans, such as longer water pump life and reduced parasitic engine load.

Generally you want the highest CFM possible. The problem is that the CFM ratings are rated at Free Air or at some unknown pressure drop so comparing CFM ratings between manufacturers may be comparing apples to oranges. Two different fans with the same Free Air CFM rating may move considerably different amounts of air with a pressure drop of 0.5" water column. It doesn't take much air restriction to drop the CFM rating considerably.

As far as the current rating goes, It is probably best go with the ones with higher current ratings. Hopefully the higher current means a more powerful motor which helps keep the airflow curve flatter at higher pressure drops. With smaller motors, the fan blades slow down more as you increase the pressure drop across the fan blades. Of course a higher current draw could also just mean the motor is less efficient, but I would expect most of the cheap permanent magnet motors in these fans to be roughly equal efficiency wise.

Most fans will "push" more air through a given restriction than they can "pull" through. Pushers are usually slightly more efficient. The other advantage of "pushers" is that the fans don't get the hot air from the radiator blowing across them so they may last longer.