While the EPA doesn't necessarily recommend cleaning your air ducts unless there is visible mold, excessive dust and debris or an infestation of insects or vermin, the U.S. Department of Energy and ENERGY STAR suggest checking the leakage rate of your ducts.
Is more than 20 percent of the moving air leaking out of your system? Then it's time to have a professional seal your ducts. According to the Department of Energy, you can improve the efficiency of your HVAC system by about 20 percent by sealing and insulating the ducts. And while you're getting your ducts in order, have them wrapped in insulation for added efficiency.