Making "energy efficiency" a priority in selecting a new air conditioner will mean lower utility bills for many years to come. For most of the country, compressor-driven air conditioning systems are about the only choice, other than natural cooling or fans. The other option is an evaporative cooler, but these only work well in arid regions like the southwest.
The type of air conditioner you need depends in large part on your climate and cooling loads. In small homes and those with minimal cooling needs, room air conditioners may work well. If you are considering room air conditioners, you have a choice of one that mounts in a window or one that is built into the wall. Wall-mounted units are often the best choice (both for aesthetic and practical reasons). They cost more to install, because an "opening" has to be cut through the wall; but they are harder to "steal", do not block views and light, and will keep the window usable for ventilation.
Central air conditioners are more efficient than window or through-the-wall, types. In addition, they are out of the way, more quiet, and convenient to operate. If the home has ductwork for a forced-air heating system, you may be able to use it for air distribution. Whether or not your existing ducts will work for air-conditioning depends on its size and the relative heating and cooling loads. An air-conditioning technician will be able to advise you. When locating the outdoor compressor, be aware they can be noisy. Avoid placing outdoor units near patios or windows. Also, placing them where they get good air flow and shading will help them operate more efficiently.
- Energy Star rated air conditioners have higher efficiencies than standard models. This makes them more efficient and less costly to operate.
An "energy-saving" feature to look for when purchasing an air conditioner is a fan-only switch, which enables you to use the unit for night time ventilation. In this mode, the fan blows air, but the refrigerating portion of the air-conditioning system does not operate, substantially reducing air-conditioning costs. Some units offer a filter check light that comes "on" to remind residents to check the filter after a certain number of operating hours.
Another "energy-saving" feature is an automatic delay fan switch that turns "off" the fan a few minutes after the compressor turns "off". These kinds of features probably cost a little more, but can pay for themselves in monthly energy savings.
Heat pumps, though more expensive, offer the additional advantage of providing heat in addition to air-conditioning all in one unit. Room air conditioners come in a wide price range. Some can be purchased for as little as a few hundred dollars, while large central air conditioners and heat pumps can cost as much as $5,000 or $6,000. If duct system modifications must be made for a central air conditioner, that can add substantially to the cost.