Is It Time for a New Air Conditioner?

Today's units are more efficient than ever. Should you invest in one?

By Gary Foreman

 More than half of all homes in the United States have central air conditioning units, which is a blessing in the scorching summer months. The bad news is that it costs money to run them. Central air conditioning ranks third in total residential energy usage. Only heat and water heating consume more.

Before you replace an existing air conditioning system or buy one for the first time, take a look at three topics: air conditioner efficiency, selecting the right size air conditioner, and buying a new system.

An air conditioner's efficiency is measured by its SEER (Seasonal Energy Efficiency Ratio). The Department of Energy (DOE) defines SEER as the total cooling in BTU's divided by the watts consumed. A higher SEER indicates a more energy efficient system.

Until 1979, the average central home air conditioning system had a SEER of 6.0. By the 1990's, a minimum standard of 10.0 was set. Even higher standards currently are being debated.

As you might expect, an air conditioner with a high SEER will cost more. The DOE estimates that a unit with a SEER of 13.0 will cost about 15 percent more than one with a SEER of 10.0. But the same unit will provide 30 percent more cooling per watt consumed.

Will a more efficient unit save enough to pay for the increased cost? The DOE thinks so. It figures that operating the 13.0 SEER unit versus a 10.0 SEER will save $113 more than the additional cost to purchase it.

If you have web access you'll find the DOE's fact sheet on air conditioners at

Those who live in a warm climate might want to consider a higher efficiency unit with an SEER of 15.0 or more. It will cost more, but could pay dividends in areas requiring heavy air-conditioning usage.

Remember that SEER only measures the efficiency of the air conditioner. It doesn't take into consideration how well your home is insulated, the condition of your ductwork, or other factors that affect cooling.

Determining the correct size isn't easy. It's not just a matter of calculating the volume of air that you need to cool. The climate, style of your home, number of windows, amount of insulation, weather stripping, and shade as well as other variables all affect the size of the unit needed. It's tricky to do the calculation yourself. You really need a professional. In fact, the industry has created a formula that considers all the variables.

Air conditioners are rated in BTU's/hour or in "tons." A ton is 12,000 BTU's/hour. If a unit is too big, it will cost more to buy, more to operate, and won't do as good a job dehumidifying the air. According to the Consortium for Energy Efficiency (CEE), a national, non-profit public benefits corporation, a properly sized air-conditioning system can reduce energy usage by up to 35 percent.

The easiest way to get an idea of the correct size is to get three bids on a new system. Not only will that allow you to compare prices, it will also give you three estimates of how big a system is required.

Before calling for estimates, upgrade your insulation and weather stripping, if needed. Both will affect the cost and size calculation.

The Purchase
Check with the local electric company before making a purchase. Many offer rebates when you buy a more energy efficient air conditioner. Don't forget to consider the repair record and the warrantee offered by the manufacturer.

Should you replace your air conditioner before it quits working? According to the DOE, a 13.0 SEER unit would only reduce the electric bill by $42 per year vs. a 10.0 SEER unit. Of course that's an average.

The life of an air conditioner is calculated to be approximately 15 years so if yours is approaching the 12- to 14-year range, it might be time to begin researching a new unit.

Stay cool!

Gary Foreman is a former certified financial planner who currently edits The Dollar Stretcher Web site .