On February 21, 2011, EPA issued final rules to reduce emissions of air pollutants from existing and new boilers. For industrial, commercial, and institutional boilers and process heaters that are located at, or are part of, a major source of Hazardous Air Pollutants (HAP) (sources that have a potential to emit at least 10 tons per year of a single HAP or 25 tons per year of any combination of HAPs), Maximum Achievable Control Technology (MACT) controls are required; these boilers (depending on their classification) must meet air toxic emission standards.

The final rules represent a change from the rule as proposed. In response to strident opposition (including such claims as the rules would kill more than 300,000 jobs), EPA revised the rule for smaller boilers (less than 10 million Btu/hour) at area sources (sources that have a potential to emit less than 10 tons per year of a single HAP and less than 25 tons per year of any combination of HAPs), to require only operational tune-ups every two years. Larger boilers (greater than 10 million Btu/hour) at area sources must adopt energy conservation measures to avoid installing MACT controls. According to EPA, this focus on maintenance will adequately reduce mercury, lead, cadmium, dioxin, formaldehyde, and hydrochloric acid emissions. Although this revision helped cut the estimated cost from $4 billion, the final rule will still cost the regulated community an estimated $1.4 billion.