grow tent lighting and ventilation help?

so this is my 2nd grow and i decided to invest in a grow tent 36-Inch x 20-Inch x 62-Inch and this time i wanted to upgrade lighting to a 150w HPS only for about 3 plants and was wondering if i need to set up a ventilation system or if i could get away with just having a couple fans set. my local green life shop has a 150w sun system HPS for $55 and heres a picture of my grow tent

High pressure bulbs get a lot hotter than cfl's or flouro tubes so I would say you need an exhaust fan at the least. An enclosed fixture with a duct connection and a inline fan running out of the tent would ensure heat wouldn't be a problem. Another thing, make sure you're ballast is outside of the tent as it can add additional heat. Just run the fixture cable through the lower flaps.

how big of an exhaust fan will i need for a

• 36-Inch x 20-Inch x 62-Inch room​
  
  

A 6" duct is pretty standard and most tents come with the holes for them. The CFM on this one is plenty for that size. http://www.amazon.com/LEDwholesalers-GYO2402-6-Inch-Hydroponic-Booster/dp/B003YFADW8/ref=sr_1_1?ie=UTF8&qid=1362791524&sr=8-1&keywords=4+inline+fan

I dont think a 150w Hps is enough to cover 3 plants. id go with a dimmable 250w HPS in a cool tube and a 6" inline fan and filter. If you are gonna be using the 150w hps im pretty sure you could get away with a 4in inline fan and filter....or a 6in on a speed controller to lower noise. good luck