melki, a better determination of your next move would be to know what your average temperatures and humidity levels are in your grow room/tent and the smell factor. You say it gets cold in there; well how cold is cold? Let me give you an example based on my own personal experiences; my last two grows have been down in my completely uninsulated unheated basement where my laundry room is near. I had major temperature problems in both hot and cold seasons until I figured out how to create more constants in my setup. In the summer time and fall, my temps would get 90 degrees F and above. That's a breeding ground for ALL sorts of nasty bugs, molds, etc. On the flip side, in the winter, my temps would fall down to sub 50 degree F temperatures, which I noticed slowed down growth. From what I've read and gathered, marijuana grows best between 70-80 degrees F, but that doesn't mean it won't still grow in temps outside those ranges.
Also factor in humidity. As the other fellows stated, you really need air flow on your plants while they are growing. I used a tall Lasko oscillating tower fan until it crapped out on me; now I use three 6" clip-on variable speed fans in my setup. You can pick one up for about $12 on Amazon.com or a store comparable. Humidity aside; the resistance on the growing branches will make them stronger as they cope and adapt to their environment.
Is smell a factor? These guys will tell you how much those plants are going to stink. 5 minutes with my fans turned off turn my entire house, upstairs and downstairs, into a garden fresh marijuana aroma that takes awhile to air out. Since you are using a passive air intake, hopefully your 4" exhaust is creating a negative air pressure space inside your grow box (basically, you have more air pushing out of the confined space than you are pulling in. This causes a suction like effect that draws more air towards your exhaust instead of other exits.) You definitely want to keep that exhaust going for that fact alone, in my opinion.
