upstairs grow

If i had a grow upstairs and all the windows sealed shut, how would i bring fresh air into the grow room...would the fresh air coming from the stairs be sufficient if i had the carbon filter in the room of the grow?

As long as you put enough negative pressure, or any for that matter, it'll suck air from wherever. As long as you dump that air outside you're getting fresh air everytime.

You could run a vent from the basement into the grow room. That'll give you a nice source of cool air.