Vissani VWA10 (Home Depot)

An inverter compressor runs at variable speed, ramping up and down as needed potentially reducing energy consumption.

Much like the remotes for home-entertainment devices, these wireless devices control almost any function on the unit. They're especially useful if access to the air conditioner is limited, as when the unit is mounted through the wall at ceiling level. The remote generally works well anywhere in a room, although some may not work as well when they're used far to one side of the air conditioner.

A growing number of air conditioners now have electronic controls. Much like the digital thermostats for heating systems, these can (fairly reliably) hold the room at a certain temperature, shown on a digital display. Many also include a timer feature that allows the user to set an "on" or "off" time--great for, say, having the air conditioner activate automatically to cool a room before you return home from work.

This feature automatically varies fan speed according to differences between room temperature and the thermostat setting. When the difference is wide, the fan runs at higher speed; when the gap is more modest, the fan runs more slowly. The speed will change automatically as needed, to respond to changes in selected setting or room temperature.

This indicator light or flag signals when the filter needs cleaning. It's usually triggered after a certain number of hours of operation have elapsed on the internal clocks in electrical control models. Flag-type indicators can activate in the event that dirt and debris blocks the filter.

Indicates which direction the air conditioner blows cool air best. Direction given is when facing the unit. "Even" means that the unit was equally capable blowing cool air in either direction.

U-Shaped air conditioners allow the window to be lowered further when the unit is installed potentially providing reduced noise levels and improvements in sealing the ac in the window.

The unit's cooling capacity, as supplied by the manufacturer (and as certified by the Association of Home Appliance Manufacturers, AHAM, unless otherwise noted in the Recommendations & Notes). Capacities range from 5,000 British thermal units per hour (enough for a modest-sized bedroom) up to 12,500 Btu/hr. (adequate for a large, sun-drenched room or even two interconnected rooms).

The energy-efficiency rating, as supplied by the manufacturer (and as certified by the Association of Home Appliance Manufacturers, AHAM, unless otherwise noted in the Recommendations & Notes). The higher a unit's EER, the lower its operating cost compared with other models of its size.

The minimum and maximum window-widths into which the air conditioner will fit. If your window opening is narrower than the minimum width, the air conditioner will not fit. If your window opening is wider than the maximum width, the side panels will not cover the entire opening.

The combined energy-efficiency rating, as supplied by the manufacturer (and as certified by the Association of Home Appliance Manufacturers, AHAM, unless otherwise noted in the Recommendations & Notes) which calculates the model's efficiency when combining operation in cooling and standby modes. The higher a unit's CEER, the lower its operating cost compared with other models of its size.

The minimum and maximum window-widths into which the air conditioner will fit. If your window opening is narrower than the minimum width, the air conditioner will not fit. If your window opening is wider than the maximum width, the side panels will not cover the entire opening.

In general, smaller-capacity models are lighter, while larger-capacity and some high-efficiency models tend to be heavier.

A feature usually found on larger and heavier models, in which internal components are mounted on a chassis that's removed from the outer enclosure (cabinet) through the front face (grille). The cabinet must be installed into the window opening before the chassis can be slid into place. That makes for a more secure but slower installation, and for easier access to components requiring service and maintenance.

The minimum window height into which the air conditioner will fit. If your window opening is shorter then the min height the air conditioner will not fit.

This provides additional support for the air conditioner, which otherwise is held in place only by the window's upper sash. The bracket's angle can be adjusted to the particular windowsill and to allow condensate to drain properly.