People might think that closing the air vents can prevent the cold air outdoor coming to the house and help them to save the energy cost. However, this action does not help to keep the cold air away and lower your bill. If you closed the air vent, the pressure load will increase dramatically; it will lead to the result of overloading the conditioner and minimizing its efficiency. Furthermore, the air conditioner is still operating after you closed the air vents which mean it tales the same or even more amount of energy as the cooling fan remains operating. Not only the air conditioner but the ductwork will be damaged as well. Hence, we do not recommend people closing the air vents even in the unused rooms. It is not worth as the damages might cause more than you can save from it.