Hi there. Am VERY new to all of this, and was hoping someone may be able to give me some advice relating to my current issues & concerns, re: indoor growing... Okay. I am creating my first grow room at the moment. Currently, what I have is: 250W HPs (w/ ballast, etc) Mylar Grow Tent (45x80x160cm) or roughly, 1.5x2.5x6ft (very rough) with black casing. The tent is completely light proof. Now, my concerns come in relation to the ventilation system, and heating/cooling... With a grow tent of this size, and a 250W HPS, what sort of ventilation and cooling should I be looking at? The tent has a 150-200mm opening at the bottom left for Air Intake, and another at the top right, for Exhaust... What I was considering, and wanted to see if this would be suitable - getting a 21W 150mm inlet fan and installing this as the exhaust fan... Then, I was thinking I could just leave the intake hole empty, for passive intake. The intake hole would face the centre of the bedroom - with window open... Would this be okay, or would I need to have the same fan there for intake, as I put for exhaust? Also, if I were to do this, would it remove any problems I may have regarding heat, as a result of using the light??? And also, if I were to install just the exhaust fan, and ducting, and were to run the ducting over the top of the tent, and position it to blow directly out my window, through a fly screen, would this work? I am hoping someone may be able to assist me with this... And also, in regards to air movement, within the tent... Would the exhaust fan take care of all of this, or would I need other fans inside the tent as well??? A few ppl have told me that by only putting an exhaust fan of this size, at the top, it will suck the 'used' air out, and blow it (wherever i direct it), whilst, at the same time, sucking fresh and cool air through the intake hole (without the need for an intake fan)... Is this correct? And if so (and again, if not) will I need smaller fans inside the room to circulate air & create movement, or will the suction from the exhaust fan simply drag the fresh air across the plants (as the holes are on opposite sides of the room)??? If I do need fans for inside the tent, will the small, crappy PC fans work sufficiently (perhaps, 2 in there; in the sides/corners not already used by the intake/exhaust holes??? Ultimately - I have the 2.5ft X 1.5ft X 6ft Mylar Grow Tent & the 250w HPS with ballast, etc... I am trying to make it as stealthy as possible, and hoping to minimise electricity costs (as much as possible, anyway)... So, simply put - what do you guys (the experts) recommend in regards to controlling the airflow, odour & temperature of the tent? Primarily being the airflow/ventilation... I am hoping that, by solving the intake/exhaust problem (or knowing what to do) I may be able to reduce, or even better, remove, the need for cooling, or fans inside... If it helps, or affects your recommendations & advice, it is currently winter here, and (probably) averaging about 14-22 degrees Celsius (and perhaps a little lower at night)... Any help would be most appreciated... I know there are other feeds & posts explaining some of the things I have asked, but none seem to apply for a room of this size, or Australian Winter temps, etc... Thanks in advance.