Air Flow Issues

Hi guys, I have a grow that is identical in every way to last time except this time I'm not using my Centrifugal fan (for noise worries), so the air flow will be nearly stuff all...
There is gaps in things that air can get in, but my guess is minimal.. Can this have a major impact on slowing down growth or not a huge amount..!!
Any advice appreciated....
(P.S it's actually a mates prob but for ease I am saying me)

fresh air is our friend

Yeah my thoughts too.. I was just not sure if it made that MUCH of a difference or wether it was as important as water..