ventalation questions!

hi this is my first grow and currently has no top or ceiling, however i do have a fan running to blow the air about the light hangs over the box so do i still need a ex fan? science says hot air rises so it seems logical that i dnt need one! please any advice is crucial so i dnt keep going into my grow and have it ruined!!!!!

Go get a thermometer and hang it from the light, 2 ft from the reflector. Now you have a gauge that will show you the temperature and how high the light should be to the tips of the plants. You should look at the temperature if its too far above 30 C I'd say you have a problem.

Just don't put the sensor in direct light because it will give you false readings. It will absorb radiant heat. Ambient temps are what you want to measure. To check radiant temps simply place your hand over the top of the plant with the back of your hand facing up. If it is uncomfortable in 30seconds or so then the light is too low/hot.

With a cool tube I can put the back of my hand on the glass 1/2" from the 400w MH bulb and hold it all day... but I don't want cancer, thanks!

yea its not too hot but i didnt know if it was ok or not.