From what I have read, you dont want the vent fan on a timer. it should be running all the time to vent not only heat, but the gases released by the plant and to draw fresh air over the leaves. I use a passive intake from my basement and vent it outside next to the drier vent. I can feel the pull from the cat flap in the door into the basement as exhaust runs.
The only reason I need that fan is to cool the cooltube. I have a duct tied into the return of my HVAC system that pulls in the tent air at a high rate. From there it is UV sterilized, filtered and then it goes through an airknight. The house does not stink, I dont even need a charcoal filter in the tents.
Under other applications you are spot on, my 2x4x5 veg tent will have the T5 with a totally passive intake setup...which still manages to suck the sides of the tent in.
My flower tent 4x4x7.5 is running a 1000W HPS, 12/12. So I plan on running the vent fan 12 hours 15m a day (leave it on 15 minutes after the light turns off to ensure it is cooled). With the duct pulling air from the tent into my HVAC system I should be ok with air movement....not to mention all the little fans I have running in the tent.
Oh, my apologies....I got to blabbering. Thank you for your input as always, I dont mean to come off like a you know what....text just sometimes cant translate emotion. Green Mojo to you!