4 CFH (assuming this is not SCFM) can be converted to L/min. According to the book "Yeast" by Chris White and Jamil Zainasheff, at 1 L/min for 1 minute, 20 L of wort (~5 Gallons) will be aerated to ~9.2 ppm O2.
So at 4 CFH * 1 hr/60 min * 28.3 L/ft3 = 1.87 L/min of O2
Run that for about 60 seconds through your wort and you'll be good. If it is SCFM, then you need to adjust for temperature. But you can still find out exact numbers with some calculations.
Hope this helps!