Page: 1 of 5

The basics of air conditioning

As summer draws near and temperatures creep upward, a home air conditioner may start to look like more of a necessity than a luxury. All air conditioners work basically the same way as your refrigerator: They pump heat from one area (in this case, your home's interior) and transfer it to another (the outdoors). An air conditioning system contains several parts:

  • The evaporator in a winding coil, usually made of copper, that draws out warm air from indoors.
  • The condenser ia s separate coil that releases the collected heat outside. This coil is surrounded by aluminum fins to disperse the heat.
  • The refrigerant is a liquid that transfers heat from the evaporator to the condenser. It evaporates in the indoor coil, pulling heat out of the air, and turns back to a liquid in the condenser, releasing its heat outdoors.
  • The compressor is a pump that forces the refrigerant through this network of tubing and fins. This is the part of the system that uses electricity.

In a room-sized air conditioner, all these parts are contained in one compact unit that sits in a window (or can be installed permanently in a wall). These units are much cheaper than a central air conditioning system and are easy to install. However, they only have enough power to cool a single room. We cover these AC units in a separate report.

If you need to cool an entire home, a central air conditioner is much more efficient than a window unit in each room. Central air conditioners also make less noise and are easy to use. However, they are much larger and more complicated to install. Unlike a room air conditioner, which is an easy do-it-yourself task, a central air conditioner must be installed professionally.

This can add thousands of dollars to the sticker price. In addition, a central air conditioner requires a system of ductwork to send cold air throughout the house. If your home has forced-air heat, then the ductwork is already in place; if not, adding it will increase the cost of central air conditioning.

In general, consumer publications do not test central air conditioners. HVAC professionals generally agree that proper installation and maintenance are at least as important to the performance of an air conditioning system as the unit itself, so testing in a lab would provide little useful information about real-world performance. However, we did find a few sites run by HVAC professionals, such as and, that recommend specific air conditioning units based on factors such as features, efficiency and warranty.

We also found the results of a reader survey that evaluates the reliability of specific air conditioner brands. also rates and ranks air conditioner brands based on individual user reviews. Finally, we turned to the Energy Star website, run by the U.S. Department of Energy and the Environmental Protection Agency, for information on the energy efficiency of specific air conditioners. Together, these sources enabled us to choose six top air conditioners that combine efficiency, durability, strong warranties and quiet operation.

Back to top