Most homeowners know their heating, ventilation and air-conditioning system should be clean to keep efficiency up and pollution down. Many, however, don’t know how it’s done. The most effective way to clean air ducts is to have a professional contractor use a powerful, specialized vacuum. While the vacuum draws air through the system, devices inserted into the ducts dislodge any debris stuck inside them. To find a professional cleaner nearby and to get a free “Homeowner’s guide to air duct cleaning,” go to breathingclean.com.