Air conditioning is one of those amenities that’s easy to take for granted if you have it, and—on a hot, humid summer afternoon—easy to covet if you don’t. In fact, in relatively warm climates, central air conditioners have become more the norm than the exception. In addition to cooling, they dehumidify and filter air, making it more comfortable and cleaner.

For those who aren’t familiar with the term, a central air conditioner works from a central location to distribute conditioned air throughout a house. Unlike a small, window- or wall-mounted room air conditioner, designed to cool a single room or small area, a central air conditioner borrows a central air-handling unit such as a forced-air furnace or heat pump and ductwork to deliver cooling throughout the entire house.

A heat pump is related to an air conditioner. It is essentially a central air conditioner that can be reversed in winter to heat a house. Both air conditioners and heat pumps use refrigeration technology to achieve the transfer of heat or cold. For more about how refrigeration works, see How a Central Air Conditioner Works.

The first decision you will face when choosing an air conditioner is whether to opt for a whole-house air conditioner, one or more room air conditioners, or a heat pump. For more information on the pros and cons of each, see Air Conditioners: Central, Air Conditioners: Room, and Heat Pumps. To help you make an informed decision on the right type to get, see Air Conditioners: Central or Portable'

Central air conditioning is the most popular of the options, particularly for a home that is already equipped with a forced-air heating system or, even better, an existing whole-house central air conditioner.

Manufacturers produce whole-house central air conditioners in a range of sizes, which raises one of the more confusing questions you’ll face when buying a new whole-house air conditioner: How big should it be' The problem is that you want a central air conditioner to be large enough to cool your home, but you don’t want to spend more than necessary for the equipment and you don’t want the unit to be so large that it operates inefficiently. For the answer to this dilemma, see Central Air Conditioners: Cooling Capacity.

(For information on sizing a single-room air conditioner, see How to Buy the Right Size Room Air Conditioner.)

Speaking of efficiency, it is important to recognize that air conditioners are expensive to operate because of today’s high cost of energy. It doesn’t make sense to buy an air conditioner that you can’t afford to run. The name of the game is efficiency or, in other words, an air conditioner’s ability to convert energy (electricity) to cooling in the most cost-effective way.

For a whole-house central air conditioning system, see Central Air Conditioner Cost Considerations and Central Air Conditioners: Energy Efficiency Ratings.

For a room air conditioner, you’ll want to check out the HomeTips article called Room Air Conditioner Energy-Efficiency Ratings. --DV