What does your grow box lay out look like? That doesn't make a lot of sense that when you turn on your ventilation your temps get higher. Are you turning on your lights too youre saying? Whats your lighting? Grow box dimensions? Fan size/cfm?
Its 2ft width 2ft depth 4ft high. 4 Cfls 3 of them are 35w 6500k and 1 23w 2700k. The fans are 2" pc cooling fans and i dont know the cfm! They might not be good enough im thinkin. I have a passive intake and im getting a small amount of negative pressure. The lights are on 20/4 and i put the fan to circulate air on for about a half hour evry 2hrs or so, when i do the temps rise by 5c. Could i do with better extract fans? or bigger intake fans? Sry, should have been more specific.
How big is your passive intake? You should have double the area you have exhausting in passive. So if you had two 2" size holes for exhaust, youd need approx an intake the size of 4 of those holes(whole area of all intake holes).
You need some air in there get a 4 in desk fand put it to blow on the plants it will push the air around to the exhaust i had the same problem