Researchers explore pros, cons of air conditioner replacement

September 29, 2010
Jim Erickson,
Laura Williams, Phone: (734) 615-4862, E-mail:

ANN ARBOR— A University of Michigan study has created a framework for determining the optimal time to replace a central air unit to save energy, reduce greenhouse gases and save money.

The answer varies depending on climate and homeowner behavior, but can be determined by considering three questions: the age of the existing unit, how well the existing unit has been maintained, and what matters most to the unit?s owner.

In the study, the amount of operating energy saved by using more efficient equipment was compared to the additional energy needed to manufacture and deliver the unit as well as dispose of the old air conditioner. The researchers then considered the cost to the consumer of purchasing a new, more efficient unit rather than continuing to use an older model.

Research associate Robb De Kleine with U-M?s Center for Sustainable Systems conducted a life-cycle analysis of central air conditioning Greg Keoleian, co-director of CSS, and Jarod Kelly, Alcoa Foundation Conservation and Sustainability Fellow. The research team pinpointed the time when the cost of using an older unit ? in terms of out-of-pocket expense, impact on the environment and household priorities ? outweighs the cost of buying a new one.

To figure out when to buy a new air conditioner, answer these three questions:

1. Have you maintained your current air conditioner?
If it has never occurred to you to get an air conditioning tune-up, your air conditioner probably isn?t performing as efficiently as it could. Making sure that your air conditioning system is operating at its best can reduce the emissions of greenhouse gases by more than 25 percent as well as keep utility bills lower.

2. If you have maintained the equipment, how old is it?
Even if you have doted on your air conditioner, it will eventually need to be retired. If you currently have a typical cooling system installed in 1992 or before, replace it; the average air conditioning system sold today is considerably more efficient and replacing will significantly reduce cost, energy consumption and greenhouse gas emissions. Your bills will be lower and the impact on the environment reduced, and you will soon recoup the costs of purchasing and installing the new unit.

3. What matters most to you: saving money, consuming less energy per month or reducing greenhouse gases?
In general, if your goal is to reduce energy consumption associated with manufacturing and operating a central air condition over its lifetime, you should replace your unit more frequently than if your priority is reduce your expenses. However, more frequent replacement means an increase in greenhouse gas emissions, so balancing your priorities will be part of your purchasing decision.

About a third of central air conditioners in single-family homes are at least a decade old. Meanwhile, the typical central air conditioner purchased today is rated as being about 25 percent more efficient than systems purchased 10 years ago due in large part to more stringent federal energy efficiency standards. If households nationwide adopting an optimal schedule of air conditioner replacement, energy use could be reduced up to 7 percent, greenhouse gas emissions up to 4.5 percent and costs by about 2.5 percent, according to the study

“A homeowner starting with a new unit in 1985 and replacing it every 13 or 14 years thereafter can come reasonably close to achieving the lowest impacts,” de Kleine said.

The report, which was funded by The Energy Foundation and the Alcoa Foundation Conservation and Sustainability Fellowship Program, can be found at

About the Center for Sustainable Systems
CSS advances concepts of sustainability through interdisciplinary research and education. CSS collaborates with diverse stakeholders to develop and apply life cycle based models and sustainability metrics for systems that meet societal needs. CSS promotes tools and knowledge that support the design, evaluation, and improvement of complex systems.

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