hi everyone im pretty new to the forums but couldnt pass this thread up.. about 20 yrs ago i made a 4x4x8 box out of white sty-ra-foam and cut a square hole in it to access it and put a osculating fan out side the hole to blow on the plants. so this looked like a dog house so to speak . anyways . i grew 15 plants in 2 or 3 gallon containers cant remember witch on the size but i used soilless mix . of vermiculite and perlite. i supplied the nutes . and i only used a 400 watt mh . i only grew them about 12 inches tall and then flipped them to 12/12 and i ended up with about a oz per plant. when all done . oh and these were clones so i knew they were all gurls going in. so to answer your question on growing 15 plants with one 600 watt . yes u can i did it with a 400 watt . but i dont know if it worked cause of the soiless mix or because of the height of the plants or both. all i had for ventilation was a squirrel cage fan above going in to the attic. it was a apartment so i didnt care if mold formed in the attic. i believe i kept the 400 watter about 18 inches above the plants . hope this helps... cheers 
