Central Air

• Most new homes come with central air conditioners.new,home,house image by Greg Pickens from Fotolia.com
  
  Most central air conditioning systems should cool a moderate, four-bedroom house by about 10 degrees Fahrenheit in three hours. This is highly contingent on a number of factors, such as the age of the system and the temperature outside. Regardless, the house should get noticeably colder within a few hours. If not, there could be something wrong with your air conditioner.
  
  

Individual Unit

• Many older homes don't have central air.old home image by pearlguy from Fotolia.com
  
  An individual unit can cool a room in less time than a central air conditioning unit typically can, if the door and all of the windows in the room are closed. A relatively small, 10-by-10-foot bedroom should become noticeably colder in 20 minutes, reaching a more comfortable, colder temperature in about an hour.
  
  

Evaporative Cooling

• Evaporative cooling for those who live in dry climatescolorado river image by Don Lewis from Fotolia.com
  
  Evaporative cooling systems are different in that they cool air through the evaporation of water, rather than through vapor-compression or water-absorption cycles, like most typical air conditioning units. These systems are good to use in hot, dry climates. When compared to traditional air conditioning units, evaporative cooling systems tend to take longer to cool a desired area as well, as the air is cooled in spaced-out cycles. About 15 cooling cycles occur per hour, so the desired temperature may not be reached for a few hours or more depending on the size of the home.
  
  

Power

• Newer air conditioners are more powerful and efficient.Sch?¡èferhund image by Angelika Bentin from Fotolia.com
  
  The time it takes an air conditioner to cool a home also varies according to the system's power, measured by its Seasonal Energy-Efficiency Rating. One of the greatest influences on a system's SEER is its age. The typical system produced in the 1990s has a SEER of 6, while systems produced in the early 2000s typically hold a rating of 10. Any system produced after Jan. 23, 2006 has a SEER of 13 or higher.
  
  

Other Factors

• Drafty windows and poor insulation?small house, big house image by Nino Pavisic from Fotolia.com
  
  A number of other factors affect how long an air conditioner will take to cool a home. These include the home's age, insulation, and whether doors and windows are open. The time it takes an air conditioner to cool a house also depends on the outside temperature.
  
  

Tips

• Just one window dramatically taxes your system.windows image by christophe morgado from Fotolia.com
  
  You can increase the efficiency of your air conditioning system by keeping all air conditioning vents open, windows of your home closed and the doors to each room open. Closing vents or doors to certain rooms traps heat and make the air conditioning system work harder. Also, have your central air conditioning system serviced at least once every couple of years and be sure to thoroughly clean all systems once a month while they are in use. In addition, having a well-insulated home with proper window sealing will improve the air conditioner's performance.