I am growing a couple of midgrade bag seeds for experimental purposes and my 18"x18"x18" veg box has a temp of about 86 F with the door closed ( I am only using a 26=100W cfl that isnt putting off much heat) and within seconds of opening the door it drops to like 78 F which is ideal. But considering that my bulb is cool white natural light i dont understand why the box stays so hot.....any ideas?

They still put out extra heat and if you don't vent it heat will build up, although 87 or whatever you said isn't that bad really.

you need fresh air intake near the bottom,,and an exhaust HoLE near the top,,also a small fam blowing air around inside would be ideal,,cfl's do get warm,,but your two plants need fresh air,,good thing it is only an experiment,,because 1 26 watt will just grow you a nice looking weed plant,,and it will take a while,,also,,,opening and closing your door too much may not be a good idea,,you want the temps constant,,not dropping 10 degrees and climbing back up,,dropping again,,back up,,hope this helps

Keep on Growin

HoLE

Definitely make vents and add exhaust fan. 87 degrees won't kill the plant directly, but it will stress it out and slow growth. I have a cabinet almost the same size and it has a vent at all 4 corners with 2 computer fans moving air out the upper vents all the time, keeping it only 3-4 degrees above ambient temp. In a small cabinet, temps are the main limiting factor because heat stress stops growth and exacerbates other minor problems. Likewise keeping it cool lets you up your light wattage and hours of light leading to the results you want .

yeah i prolly do need a fan but i have 2 separate boxes that are like 1'x1'x2' (1 for each plant) and it is hard enough to fit the pot and light in each. I just got a batch of 6 thai plants ripped up by my dad so i am trying to be super discrete til that blows over. I ate it though b/c they were 3 wks and 9'' with like 7 sets of leaves. I have made ventilation as suggested.

btw i now have a new bubbletub setup in my closet and i just got my new thai seeds so i was just fuckin around waiting on them. I was just trying to see if i could use these small boxes ( actually cabinets on my tv stand) to germ and start off my new seeds in rockwool and then add them to them to the tub when the roots get bound because they can't get more than 8" in there without being burned by the light. Within a couple of weeks im gonna start a journal for my big budx northern lights (2 wks) and new chocolate thai plants