Here are some guidelines on what the 13 SEER standard may mean for you:

Bigger systems, higher up-front cost. Air conditioners usually grow larger as the SEER rating is increased. In order to achieve a higher efficiency, manufacturers need to install more coils to more efficiently transfer heat. More copper, aluminum, and steel mean a higher-priced unit. Higher-efficiency air conditioners often use more advanced technology and have more features, so this makes them somewhat more complicated, and possibly more expensive, to install. But some of these technologies and features enhance comfort, convenience, efficiency, and reliability.

Lower operating costs. A central air conditioning unit rated at a 13 SEER uses up to 30 percent less electricity than a 10 SEER system. With higher energy costs predicted in many parts of the country, consumers will have that payback on the unit much quicker with less electricity being used. The tips below can help you find the right hardware and technician to install your system, whether you're replacing an older air conditioner or installing one for the first time.

If you're replacing an old central-air system, you can expect to pay $3,000 or more for the equipment. If you need ductwork installed because you're starting completely from scratch or are upgrading a forced-air heating system, expect to pay thousands more.

Improving the system's air-filtration capabilities is also easiest to do as part of a general upgrade. Check ratings of air filters and whole-house units for those that combine value and efficiency.

Here are other factors to keep in mind:

• Match new equipment. Since energy costs are not likely to drop in the foreseeable future, you should consider replacing your entire cooling system when faced with a major repair of your old system. If you replace only the condenser (the outdoor unit that houses the compressor, the condenser coil, and a cooling fan), you have a "field-matched" system that can be less efficient than advertised and that may require more repairs because of undetected incompatibilities between the two. Replacing the cooling coil attached to your furnace (sometimes called the indoor coil or evaporator coil), or the indoor blower coil (a blower and evaporator coil inside a cabinet) if you don't have a furnace, add to the cost but is the only way to ensure you will get the efficiency you want.

• Consider compressor type. A reciprocating compressor is more trouble-prone than a scroll-type one. Scroll-type compressors also tend to be higher in efficiency and quieter than reciprocating compressors. Check the product literature for compressor type.

• Inspect ductwork. Leaky ducts can dramatically decrease energy efficiency of your central cooling and heating systems. Sealing and insulating ducts can cut cooling and heating costs by 40 percent per year. Insulate ducts in unconditioned spaces with R-6 duct insulation. Have a contractor seal all seams and joints in the duct distribution system.

• Zoned-system concerns. A large or multistory house is often divided into several heating and cooling zones to improve temperature control. However, this type of system is complex and has many more moving parts and controls, so it may require more repairs.