Remove standing water under cooling coils of air handling units by making sure that drain pans slope toward the drain. If humidifiers are used, they must be properly maintained. Air handling units should be constructed so that maintenance personnel have easy, direct access to heat exchange components and drain pans for proper cleaning and maintenance. Steam cleaning and other methods involving moisture should not be used on any kind of duct work. Some duct cleaning service providers may propose to introduce ozone to kill biological contaminants.
Ozone is a highly reactive gas that is regulated in the outside air as a lung irritant.
However, there remains considerable controversy over the necessity and wisdom of introducing chemical biocides or ozone into the duct work. Simply 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 other areas of your home. Some people may react negatively to the biocide or ozone, causing adverse health reactions. Chemical biocides are regulated by EPA under Federal pesticide law. A product must be registered by EPA for a specific use before it can be legally used for that purpose.