what tempurature would effectivley kill a plant?

the way my box is setup ventilation is a little tough, temps are usually a steady 90, and if i open it up and let some ventiliation happen i can get it to around 85ish.

what temps would effectivley kill a plant? theres a table fan inside blowing on the lights and a 4" personal fan as an exhaust. the back of the box is open on the bottom too as well as a hole drilled in the top of the back of the cab.

would adding one more exhaust on the opposite side of the box help reduce temps? or should i make it an intake.

also, would adding co2 help my plants cope with 90degree temps? i mean just a simple 2litre bottle, yeast, sugar, water generator. i also have many many co2 cartridges from the pellet gun days but no way to disperse them slowly enough

anything above 90F for long periods .

so what should i do about adding another fan?

I used to try growing in an attic. In the summertime the temps would be in the high 90s with the light off and the low 100's with the light on. It got over 110 in there many many times. None of my plants died from it, but they did grow considerably slower than they should have, and they were more yellow than green.

An exhaust fan ported at the top will help considerably. can pick up a cheap inline duct booster at home-depot or whereever.

if its a small box, apc type fan would do the trick

What lighting are you using ? - STELTHY

marshall guitar cabinet, 3'x3'x1.5'

4 cfls, 23w each. getting some 6500ks soon, keeping the wattage about the same tho