Wanhao i3 v2.1 stock 40mm fan rear mounted duct

##WARNING!
###Resent testing showed a major flaw!
>As I've mentioned in description below using this duct at 100% fan may cause nozzle temperature drop by 5 degrees. I've done some research and found out that this is most likely an indication that the actual temperature drop caused by the cooling flow is much higher, so high in fact that there isn't enough power to fully compensate (as a result a 5 degrees drop remains), thus printer consumes much more power and __all of it goes through a si