Growing in basement and air circulation

Hey fellas, first time grower here. The only place I can grow is in my basement which is a daylight basement with 3 windows and a door all on the north wall of my basement. It's also about 900 square feet. I germinated 3 seeds and it looks like only one is taking. It's about 2 inches high and is just starting to sprout first leaves. I'm fine with it as I knew there would be a lot of trial and error until I get the process down.

My question is one of air circulation. How much do I need for this stage and for future stages? Will a cracked window suffice. Right now what I'm doing is everytime I check on them I open the door for a few minutes but concerned that may not be enough. That's probably about 5 times a day. I also have a 10 inch oscillating fan that is pointed a little above the plants running at all times.

Any suggestions are appreciated.

Bumping, anyone?

Sure, When they are small, say under a foot tall you dont need anything, It when they get larger they use up the available co2 in a room pretty quick.
I had 8 in a 10x12 room that got about 2 feet tall and stopped growing. I opened a window and with a fan got some air in there and off they went.

Thanks Cruzer, easy enough.

That kind of leads me to my next question, I'll have a 400W MH bulb going in an air coolable reflector within the next couple weeks. Being that my basement is about 900 sq ft, do I still need to ventilate?

Probably not, I would assume your basement stays pretty cool right?
I doubt it would raise the temp 5° in 900 sq ft.