Are you vegging and flowering in the same tent? Are you pressed for time to have them flowering at a specific time and what's the size of setup and watts you using again bro? Don't know if you told me prolly did but you how stoners minds can be
that exhaust fan is a nice high velocity fan and depending on the size of your setup and watts used should work just fine.
I started back growing last year around this time and it wasn't this cold but temps didn't get bad till like April but the proper stuff and all that can be managed.