I use that fan to cool my 400 watter so it should be more than enough to cool a 250. But Ur right, it is the duct booster ur thinkin of, and no they don't put out as much as they say. They pulled a sly one on that fan, advertising it as a 250cfm but it's REALLY 160cfm unless used with a 'booster' fan, THEN u get the 250. and ya those high power inlines from htg are spendy too. How much cfm is this valueline ur talkin about? Got a link for it?