Air conditioning does more than cool the air. It truly "conditions" it by removing dust and dirt as the air is drawn through a filter. Air conditioning also lowers the humidity, making the air more comfortable at any temperature. These benefits, however, can be costly. Depending on your region of the country, air conditioning can account for anywhere from 5 to 50% of your household budget. Because an air conditioner is such a sizable investment, you can save money and energy by carefully purchasing and operating your air conditioner.
When shopping for an air conditioner, first consider what system best suits your needs - central air conditioning or room air conditioning. Central air conditioners are located in one part of a building, but they cool the entire building either by blowing cold air through ducts positioned in each room, or by circulating cooled water through pipes to each room where fans blow air across the pipes. Room air conditioners work in the same way, but have a smaller capacity and therefore only cool the immediate area.
Central air conditioners generally provide the greatest comfort but they also cost more than room units. If several rooms need to be cooled, however, a central system is probably the best buy. Central systems generally are not cost-effective as an addition to an existing home unless the existing ductwork can be used.
Room air conditioners are mounted in windows or built into an external wall. Room units are less expensive than central units; however, they only cool the general space in which they are located. There are three types of room units; window models can be installed in most windows; casement window models, used in narrow, vertical windows, usually require the removal of a window panel for installation; and built-in models which are encased in a sleeve installed in the wall.
After selecting the optimum unit type, consider unit size. A bigger unit is not necessarily better, because a unit that is too large will not cool an area uniformly. Also, an oversized unit will cool an area too quickly, causing the air conditioner to frequently turn on and off. This wastes electricity and money. In addition, a unit that is too large will not run long enough to reduce humidity and, instead of feeling comfortable, the air will feel cold and clammy at the normal thermostat setting.
On the other hand, you should avoid purchasing too small a unit. An insufficiently sized unit will run constantly on hot days and still not be able to cool the area adequately.
In sizing an air conditioner for your home, consider the dimensions of the area to be cooled and how the area is used. Based on size alone, an air conditioner generally needs 20 Btu for each square foot of living space. For instance, to air condition a room that is 15 feet wide and 20 feet long, you would calculate: 15 x 20 x 20(Btu) = 6,000. Thus, an air conditioner with a 6,000 Btu capacity would be required.
Calculating Btu requirements becomes more complicated when you consider an area's use. For instance, if you use passive cooling techniques such as shading, ventilation or vegetation, your Btu estimate can be lowered. Likewise, your Btu needs are increased by factors such as the size of the household, frequent use of heat-producing appliances, or summer humidity levels. An appliance dealer will use these factors to adjust your estimated Btu requirement. For most efficient cooling, purchase a unit, with a capacity within 5% of this estimate.