the primary concern with exhausting in the same space as your intake is drawn from is that you will effectively "use up" the amount of available C02 in the environment unless you have a way to continually provide fresh air to the room.. a window with a small fan in it would be acceptable, but you claim you have no way to exhaust outside which implies that you dont have access to a window so you may need to look into supplementing C02. also you do not need an intake fan, dial in your extraction fan to create a small negative pressure- enough to suck in the sides of your tent a little but not aggressively, if your temps rise you will need to figure out another solution for cooling, do not change the fan adjustment, your extraction fan is for managing proper air exchange, not cooling.