I think the rule is to exhaust up high and make your intake come in low. That way the high temps rise and get sucked out, and the fresh cool air comes in low. I think it would be fine to leave one end of the hood open to suck grow room air in. The hot air you are trying to eliminate won't have anywhere to go anyways. For an intake I just used a 20"x20" vent low on the wall and a box fan pulling air in through a filter. Also be careful venting hot moist growroom air into an attic because of mold risk to your entire home. I never really had to deal with smell when I was growing DP's Master Kush.