If your air conditioning contractor makes general claims about the health benefits of duct cleaning, you should know that such claims are unsubstantiated.
Other things you should know when you're considering a duct cleaning:
• Duct cleaning is not a routine part of heating and cooling system maintenance.
• EPA neither establishes duct-cleaning standards nor certifies, endorses, or approves duct cleaning companies.
• Before you hire a contractor, check with your state’s department of professional regulation. Many states, including Arizona, Arkansas, California, Florida, Georgia, Michigan, and Texas, require air duct cleaners to hold special licenses. Other states may require them as well.
• It is normal for air return registers to become dusty as dust-laden air is pulled through the grate. This does not indicate that the air ducts are contaminated with heavy deposits of dust or debris. The registers and the duct region surrounding the registers can easily be removed and cleaned. This is always a recommended practice.
• Some homeowners may want their air ducts cleaned simply because it seems logical that air ducts will become dirty over time and should occasionally be cleaned. While the debate about the value of periodic duct cleaning continues, no evidence suggests that such cleaning would be detrimental, provided that it is done properly. However, if a service technician fails to follow proper duct cleaning procedures, duct cleaning can cause indoor air problems. For example, an inadequate vacuum collection system can release more dust, dirt, and other contaminants. A careless or inadequately trained service provider could damage the air ducts or heating and cooling system.
Unresolved Issues of Duct Cleaning
Question: Should chemical biocides or ozone be sprayed into air ducts?
Some chemical companies sell products for air duct cleaning that claim a chemical biocide should be applied to the entire inside surface of the air ducts to kill bacteria (germs), and fungi (mold) and prevent future biological growth. Typically, anything that kills living organisms like bacteria and fungi is also not healthy for humans. The widespread spraying of such compounds into the air is not a good idea unless the building is unoccupied for a substantial period of time after spraying. Even then, these killing compounds could be distributed on eating surfaces and food supplies and thus affect inhabitants.
Exposure to biocides is even more of a problem for pregnant or nursing women and small children. Technicians performing the spraying must wear protective breathing apparatus. Because the long-term effects of biocides are unknown, EPA has not approved any substance for this type of application.
Mold spores and bacteria are naturally occurring and are always present in the air. A one-time killing of bacteria and mold will not prevent a recurring problem, because new bacteria and mold spores will simply start re-growing in the water and dirt remaining in the duct work. Removal of the source of water and dirt (the food supply) is the only real solution to preventing recurring problems.
Both EPA and Franks Air Conditioning recommend complete removal of any wet or moldy duct board or fiberglass insulation. Franks Air Conditioning also recommends treating replacement duct board or insulation and the surrounding fiber board and insulation with a porous duct sealant. You do not need to use this duct sealant to treat the entire duct system but just to spot treat and seal problem areas.
Some manufacturers propose introducing ozone to kill biological contaminants. Ozone is a highly reactive gas, meaning it is a highly corrosive gas that is regulated in the outside air as a lung irritant. It is not recommended to purposely introduce ozone into the air due to the corrosive and toxic properties of this gas. Many components of the air handling system would be adversely affected by a corrosive gas. There is no logical reason for the widespread introduction of either chemical biocides or ozone into the duct work. Possible problems with biocide and ozone application in air ducts include:
Little research has been conducted to demonstrate the effectiveness of using most biocides and ozone inside ducts. Spraying or otherwise introducing these materials into the operating duct system may cause much of the material to be transported through the system and released into the living areas of the structure. Some people may have adverse health reactions to biocides or ozone.
EPA regulates chemical biocides under federal pesticide laws. EPA must register a product for a specific use before it can legally be used for that purpose. The specific uses must appear on the pesticide or biocide label, along with other important information. It is a violation of federal law to use a pesticide product in any manner inconsistent with the label directions.
Question: Do sealants prevent the release of dust and dirt particles into the air?
Manufacturers of products marketed to coat and encapsulate duct surfaces claim that they prevent dust and dirt particles inside air ducts from being released into the air. Actually, you should clean duct surfaces thoroughly before applying sealant. Using sealants to coat duct surfaces is appropriate for the repair of damaged fiberglass insulation or when combating fire damage within ducts. Never use sealants on wet or dirty ducts, either to cover actively growing mold or to cover debris in the ducts. Apply sealants only after replacing wet or moldy sections of duct and cleaning the system. You can use a duct sealant which contains a biocide, to help prevent recurrence of mold. You can also use a duct sealant to spot treat and seal problem areas, but you should not spray it indiscriminately into the entire duct system, because the vapors are harmful to breathe. Follow all label directions.