So much has changed in the world of air conditioning in recent years that if your system has almost any significant breakdown — or if it’s just not keeping you as cool as it used to — it may be worth replacing it instead of repairing it.As of 2010, for example, manufacturers must use a new kind of refrigerant that’s not an ozone-depleting chlorofluorocarbon. And a new system can use less than half the electricity of your old one while doing a far better job of keeping you cool and comfortable.If your air conditioner is more than eight years old, repair is probably not worth the expense, unless it’s a simple problem like debris clogging the condenser unit or a worn fan belt. Still, to best weigh your repair-or-replace decision, ask your contractor to assess not just the condition of your existing equipment, but also the ducts that deliver the cool air and the overall quality of the insulation in your house. Improving those elements might increase the effectiveness of the system as much or more than installing new machinery.

Even if your central air conditioner is just eight to 10 years old, it could suck up to twice the electricity that even a low-end new one would use. That’s because it operates at or below 10 SEER, or Seasonal Energy Efficiency Ratio, which is the amount of energy needed to provide a specific cooling output. Until 2006, 10 SEER was standard, but these days, the minimum allowed by federal law is 13 SEER. That translates to 30% less electrical consumption and 30% lower cooling bills than equipment installed just a few years ago.For an 1,800 square foot house, a new 13 SEER unit will cost $3,000 to $4,000. You can double your energy savings by jumping up to 16 SEER, which will reduce cooling expenses by 60% over a 10 SEER unit. At $5,000 to $6,000, these super-efficient units are more expensive, but they qualify for a federal tax credit of up to $300 and possibly local incentives, too.“Your installer can run the numbers for you to see whether it’s worth the additional cost,” says Ellis Guiles of TAG Mechanical in Syracuse, New York.

“If you’re south of the Mason Dixon line, certainly, you can make up those dollars pretty quickly.”You could upgrade to the highest efficiency gear available and still not feel comfortably cool on hot days. That’s because the mechanicals are only part of the central air system. The average house’s ductwork leaks 10% to 30% of its air before it can reach your living space, according to Pacific Gas & Electric. Before deciding whether to repair or replace your condenser and blower units, your technician should run a duct-leakage test, by sealing the vents and measuring how much air escapes the system. If the ducts are inefficient, he can locate and seal the gaps, typically for $25 to $35 per vent (per “run” in industry jargon), or replace the ductwork entirely with new, insulated pipe for around $100 per run, according to Guiles. Your technician may recommend doing the duct improvements in conjunction with replacement of the mechanicals or may recommend only one or the other job.

Related: Do You Really Need to Clean Your Air Ducts?air conditioning fan running not coolingIf your house is poorly insulated, it’s putting a strain on your aging air conditioner. federal tax credit for a/c unitsResolving the house’s flaws may mean that your old system will have enough cooling power to continue to do the job for a few more years. home ac unit no cold airOr it may enable you to buy a smaller replacement system, lowering your upfront and ongoing energy costs significantly. Your heating and cooling contractor should assess and, if necessary, upgrade the building envelope. For example, he might seal gaps and cracks in the outer walls and attic floor, or he might blow insulation into the walls, either of which could knock as much as 30% off your heating and cooling costs.

Insulation also may get you a $500 federal tax credit, and in some cases, it may be a more effective solution to your cooling problems than replacing your equipment.If you decide to replace, make sure the contractor’s bid includes a load calculation, which is a computer printout showing how big a system you need and why. Air conditioning is measured by the ton, which is the cooling power of a one-ton block of ice melting in 24 hours. Some old-school installers use a ballpark estimate for sizing equipment—say, one ton for every 400 or 600 square feet of living space. But that typically leads to systems that are too big, according to Greg Gill of Action Air Conditioning and Heating in San Marcos, Calif. Not only do oversized systems cost more, but they also do their cooling work too quickly, which means more frequent on/off cycles, wearing out components and gobbling electricity. Plus, they don’t have a chance to effectively dehumidify the air. Good contractors use load-calculating software that factors in such data as the number of windows in your house, the thickness of insulation, the configuration of the attic, and the building’s orientation to the sun.

It produces not only an exact tonnage requirement, but determines how much cool air each room needs. All bids (get at least three, from licensed, well-regarded companies) should include this one-page printout. In a recent survey, homeowners said that AC & Heating Connect is a key source of information about air conditioning and heating equipment, second only to friends and family. Maybe your old central air conditioner has quit working, and you think you need a replacement.  Maybe you want to upgrade to a more energy-efficient or environmentally-friendly system. Maybe you’re not sure what to do. Whatever the reason you’re considering a new air conditioner or furnace, you’ll want to go through this handy checklist to make sure you are shopping for the right equipment and asking contractors the right questions. 1.  How much time do I really have to replace my system? Click here to learn how to put time on your side to get the right equipment for your needs.

2.  Do I really need to replace my entire system or can it be repaired? Click here to see the many factors facing the repair vs. replace decision. 3.  How much space am I trying to cool (and has it changed since the old AC was installed)? Click here to learn how you might need more or less cooling and heating power based on changes in your home or workspace. 4.  Do I want something more than “just cold air”? Click here to read about how improvements in comfort, energy costs and the environment can make you feel better and save you money. 5.   Do I really need to cool the whole house all the time? Click here to see how some common suggestions can actually lead to bigger problems. 6.  Is there really anything new in air conditioning? Click here for an overview of new technologies available today and what they mean to you. 7.  Are there unique needs in my region of the country? Click here to see how where you live might determine the type of equipment you should buy.