Q: If I buy a new energy-efficient air conditioner, how long will it take to pay for itself in energy savings?

A: The answer, of course, depends on how old and inefficient your old air conditioner is, and how often you use air-conditioning.

But in general, if you have a central air-conditioning unit that is more than 12 years old, you can expect to reduce cooling costs 30% by buying a new Energy Star-qualified unit. If you replace a 10-year-old window air conditioner with a new Energy Star-qualified unit, you may save $30 to $50 per year in operating costs.

Also: Tax credits may be available for energy-saving improvements to your home, such as upgraded central air-conditioning. To learn more about these and the government’s Energy Star program, visit its Web site, www.energystar.gov.