i would say always keep cool tubes on , exaust fans on intake fans on ,, it will circulate the air enough ... they had 200 + plants ,, im sure they had alot of HID's .. i know ppl who dont bother with anything less than AT LEAST 2 1000 W hps & they never sealed off windows .. mabye move ur opp to an interior room in the house ..get an air conditioner & vent all the incomming air to mix with stale hot exaust air & hot cool tube air ,,, ... ,, if not possible ,, id try to cut styrafoam to fit in the window sill , then cut out cardboard to fit snug in there & layer that cardboard about 5 or 6 pieces .. then on the very inside put a piece of plexi glass cut to fit percisely.. can never bee too safe