In looking through the material on the Energy Star site on ceiling fans, a couple thoughts occur to me:
CFM per watt ratings:
If you look through the CFM per watt ratings for the various energy star rated fans they vary a lot. They are provided in these energy start ceiling fan lists: Fans without lights... and Fans with lights list ...
So, I think its worthwhile to shop through the lists and find a better one. There appears to be about a factor of 2 difference between the best energy star and the worst. Non energy star fans may be far worse yet.
Use Low speed?
From the same lists, it appears that these fans move air much more efficiently at low speed than at high speed. The typical low speed flow rate is around 160 CFM per watt of input power, while the high speed flow rate is about 80 cfm per watt of input power. So, it appears the fans are about twice as efficient at moving air at low speed. To me this argues for picking a fan that is on the large side so that the low or medium speed can be used instead of the high speed. This would probably also make for less noise.
While ceiling fans offer a much more efficient means of cooling than mechanical AC, the combination of the fan and the lighting can still use a lot of power. Choosing the wrong ceiling fans might raise you electric bill a hundred dollars a year, and increase your CO2 emissions by nearly a ton if you have several ceiling fans -- so choose wisely.
I'm by no means an expert on ceiling fans, so if you think I got some of this wrong, or you have something to add, pleas drop me a line -- Gary...
Gary May 21, 2008