Choosing the right air conditioning unit will depend on the area size that you wish to cool down and if you are wanting to cool down one room or multiple rooms. The single package central air is where all the components of the air conditioner are housed in one box and usually mounted on the top of a roof but can also be attached on to a wall. Room air conditioners come in two types. The unitary is the most common and generally sits in a window or in an opening that has been made in the wall. On the outside the hot air is released whilst on the inside the cool air is blown through the room. This is only suitable for one room at a time. A larger building may have several of these. A split system central air conditioning unit where the noisy portion of the air con is placed on the outside and is less see able. This type of air con unit requires you have to have ducts to the various rooms in your home. You can then distribute cool air throughout your house at an even rate and quietly. Ductless air conditioning is obviously for homes that do not have ducts in place. You probably wont be able to cool an entire house but it will keep the air conditioning noise down by having the air-conditioning part on the outside and you can cool the area that is around the unit. An economical option for a room that just seems to stay warm or for those that may not have the budget for an expensive air con unit is the portable air con. It is nosier then the average air conditioning unit but you will be able to feel a difference in the temperature of the room. Evaporation coolers pull air through a damp pad. As it does this, the air is cooled as is evaporates the moisture that becomes attached. Before buying any air conditioning unit you should seek the advice of an expert.