| Put one up high and one down low to allow for natural convetion this will allow for natural air flow i put both at the cool end. this way you don't force the hot air out at a faster rate (saving money on power). the cooler end at the lower vent will have cool fresh air coming in and the hot end will have to fill with hot air before any heat goes out at the cool end. I am in South East Qld so it gets quit cool here. Hope yhis helps. | 
