It's official. The U.S. Environmental Protection Agency has released its new and controversial rules governing large and small boilers used at "major sources" and "area source facilities" such as industrial plants, institutions and commercial sites. The standards, which fall under the EPA Clean Air Act, will affect about 200,000 boilers, according to EPA estimates, with the vast majority of that number, approximately 187,000, being small units. Compliance isn't required until after February 2014.

A “major source” facility emits 10 or more tons per year of any single air toxic, or 25 or more tons per year of any combination of air toxics. In addition, the EPA defined 15 subcategories of “major source” boilers and process heaters based on their designs. The final MACT rule just released includes specific requirements for each of these 15 subcategories.

An area source facility is one that emits or has the potential to emit less than 10 tons per year of any single air toxic or less than 25 tons/yr of any combination of air toxics.

EPA defines large boilers as those with a heat input capacity equal to or greater than 10 million BTU/hr, and small boilers having a heat input capacity of less than 10 million BTU/hr.

The EPA anticipates the final rule to reduce emissions of a number of toxic air pollutants, including mercury, metals, and organic air toxics, which includes dioxins.Boilers burn coal and other substances such as oil or biomass (e.g., wood) to produce steam or hot water, which then is used for energy or heat. They can also burn non-waste materials but do so usually only in small amounts.

The final rule does not apply to boilers that burn only gaseous fuels or any solid waste.

To find out how the agency is working with the U.S. Department of Energy to help boiler users determine their best options, go to