In 1902 Dr. Willis Carrier invented refrigerant air conditioning. Concerned that his new invention would receive a cool reception, he staged a boxing match to attract a crowd to showcase this never-before-used technology.

Almost one hundred years later, a whopping 30 million homeowners are cooling their homes with central air conditioning. In addition, another 18 million homeowners have room air conditioners.

All air conditioners, whether window or wall-mounted units or whole-house central air conditioning systems, operate the same way. A fan sucks warm indoor air across a series of cool coils that contain a refrigerant. The cooled air is then blown back into the room. The refrigerant absorbs the heat and then exhausts it outdoors through another system of coils and fans.

For most homes, a central air-conditioning system is the most efficient and cost-effective means of cooling a home. Unfortunately, such a system can be a budget-buster for some. Still for others, retrofitting an air conditioning system is virtually impossible due to accessibility and construction limitations. Accordingly, it can be a disruptive and expensive undertaking. For these folks, one or more room air conditioners is a viable option.

The Mediterranean-style home that we grew up in, built by our grandfather around the turn-of-the-century, was a perfect candidate for a room air conditioner. Actually, it was a perfect candidate for several room air conditioners, but, for some reason, possibly cost, our parents opted to install only one.

A room air conditioner is typically mounted in a window or through an opening cut in a wall. These compact sources of hot-day relief range in cooling power from 5,400 BTUs for smaller rooms to 18,500 BTUs for big ones. They can be expensive to operate, so, if you plan to run your unit often, it's a good idea to get the most energy-efficient model available.

Location can be as important as size when it comes to cooling ability. Install a room air conditioner as far as possible from exterior doors to prevent drafts and cross-ventilation from interfering with the cooled air. Also, make sure that there are no obstructions in front of the unit, such as furniture or window coverings. Direct the vents upward to get cool air at the upper levels; the cool air will drift naturally down to floor level.

Another consideration is the power source. Most room units are designed to operate on 110 volts and can be plugged into any electrical outlet. This, however, is not the recommended means of powering such a unit. To avoid electrical wire fatigue, which can range from dimming lights to an electrical short and ultimately a fire, the air conditioner should be powered by its own dedicated electrical circuit.

Aside from the electrical work, a room air conditioner can be installed in a window in an afternoon. Most lightweight, smaller-capacity, through-the-window models come with a do-it-yourself installation kit that contains everything needed to install the unit.

Larger capacity room air conditioners and/or through-the-wall models generally require more than one person to install them and, due to the project's complexity, often are best left to a professional. In either case, there are many ways to install them. The most common installation methods include: outside flush mounting (the outer face of the unit is flush or slightly beyond the outside wall), inside flush mounting (the interior face is approximately flush with the inside wall), balance mounting (the unit is installed approximately half inside and half outside the window), and upper sash mounting (the unit is mounted in the top of the window).

Through-the-wall mounts, or "sleeves," are used to install a window-type chassis, a complete unit, or a console in walls.

Be it through-the-wall or through-the-window, a room air conditioner must have adequate support. Most installation kits come with a mounting bracket system that is first assembled and then anchored to the home immediately adjacent to the window. Sometimes, as was the case with the unit our father installed some 35 years ago, no mounting kit is provided. (Dad constructed a mounting shelf out of wood.)

The mounting support should be installed with a slight pitch to allow water to drain away from the window. Be sure to install all panels and gaskets provided with the installation kit. They will help cut down on vibration and allow the unit to operate more quietly. And, they will prevent drafts, should you not remove the unit for storage during the winter months.