Central air-conditioners use a system of coolant gases, fans and coils to transfer heat back and forth from the air inside the house, lowering the temperature when it becomes too hot and raising it when it is too cold. There are different kinds of central air conditioners, based on their ability to efficiently control temperatures throughout a house.

Air Conditioner Types

Central air-conditioners are not measured by the size of the system but by how much air they can effectively control. This is referred to as cooling capacity, although it also means how well the system can heat the air. While there are many different air-conditioner measurements, many are still measured in BTUs, or British thermal units that govern heat. Like fireplaces, central air-conditioners can produce a certain amount of BTUs per hour. While you can get a "larger" air-conditioner with more power to heat and cool a house, this is not necessarily best. The larger cooling capacity that the central air system has, the more power it will use and the more it will cost to run it. If a large air-conditioner does not match the size of your house, then not only will you be wasting money running the air conditioner, but you will be wasting energy as the system tries to heat too small a space. This will cause the central air-conditioner to cycle on and off too frequently and not dry out the air thoroughly enough. Too small, and the system will have to work too hard to heat the house. When you buy an air-conditioner, look for facts on how much space the system is designed to warm or cool, and how many BTUs it can produce. Many air-conditioners are rated per square feet, so you should also keep in mind how many square feet your house is.

Heating and Cooling Factors

Unfortunately, you cannot simply depend on air conditioning efficiency and the size of your house to decide what size of air conditioner will work for you. Every house has different heat insulation capabilities. If you have good insulation and a newer house, then you may be able to settle with a small air conditioner. If you have an older house with insulation problems or gaps, then you may need a larger conditioner to keep out with the heat gain and loss through the walls. Window insulation can also matter, and whether or not you have double-spaced windowpanes or gas-layered windows can make a big difference on how efficiently your central air system will perform. If you are in doubt, there are professional air conditioning consultants that can analyze your house and make a suggestion.

Source:

HomeTips: Central Air Conditioners: Cooling Capacity

Home Energy: Sizing Air Conditioners: If Bigger Is Not Better, What Is?

AllExperts: Is My Furnace Big Enough?