I'm sure you could replace the fan, but I really have to ask... Why would you do this? Why would you order a (fairly pricy) cooler all the way from England that is designed from the ground up to be ultra quiet only to make it louder? I don't mean to insult you, I just honestly think that this would defeat the purpose of the product. Have you already tested it and found it to be insufficient at cooling your current setup? If so, maybe try Arctic Silver before you go replacing the fan, this may lower the temp a few degrees. You may have some difficulties replacing the fan on it anyway, due to the proprietary way it attaches itself to the heatsink. Although the fan is seperate from the circular plastic base, you may end up breaking those 4 retaining pins in the process of replacing it (you could always glue the replacement on if that happens, I guess). As to which replacement fan would give you a significant increase in CFM, I'm not really sure - maybe someone else can help (it's 50mm diameter)? BTW, I'm running this HSF on a 1 GHz T-Bird and according to my mobo (MSI K7T Pro2A) it's running at a very reasonable 35/44 C idle/stress. This may be comparing apples to oranges however, since we have different mobo's and I'm not overclocking.