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Step 2: Determine Boiler's Subcategory

Step 2
Compliance requirements vary depending on a boiler’s size, age and fuel type. 

 

Determine boiler size. Boiler size is expressed in terms of rated design heat input capacity and is measured in million British thermal units per hour, or MMBTU/hr. A boiler is considered "large" if its heat input capacity is greater than or equal to 10 MMBTU/hr. 

New or existing source: Under both the Area Source and Major Source Rules, a boiler is considered a new source if construction or reconstruction commenced after June 4, 2010.   

Determine fuel subcategory. If you are not sure which fuel subcategory applies to your boiler, complete the Fuel Subcategory Calculation Tool.   

For Area Source boilers: 

  • Oil -- Any boiler that burns any liquid fuel and is not in either the biomass or coal subcategories. 
  • Biomass -- Any boiler that burns at least 15 percent biomass on an annual heat input basis. 
  • Coal -- Any boiler that burns any solid fossil fuel and no more than 15 percent biomass on an annual heat input basis.  
  • Units with an Oxygen Trim System – Any boiler with an oxygen trim system that maintains an optimum air-to-fuel ratio.
  • Limited-Use – Any boiler that has a federally enforceable average annual operating capacity less than or equal to 10 percent.
  • Seasonal – Any biomass or oil-fired boiler that undergoes a shutdown for at least 7 consecutive months every 12-month period.
  • Natural Gas -- Any boiler that burns gaseous fuels, even if it also burns oil or another liquid fuel during gas supply interruption, startup or for periodic testing, not to exceed 48 hours during any calendar year. Note that gas curtailment is excluded from the 48-hour limit. Under the Area Source Rule, there are no compliance requirements for boilers that burn natural gas.  

For a list of exceptions to the Area Source Rule, click here. 

For Major Source boilers:  

  • Liquid Fuel – Any boiler that burns any liquid fuel, no more than 10 percent solid fossil fuels, and no more than 10 percent biomass on an annual heat input basis.
  • Biomass – Any boiler that burns at least 10 percent biomass on an annual heat input basis.
  • Coal – Any boiler that burns at least 10 percent solid fossil fuel (e.g., coal, petroleum coke, and tire derived fuel) and no more than 10 percent biomass on an annual heat input basis.
  • Process Gas – Any boiler that burns process gas.  
  • Natural or Refinery Gas – Any boiler that burns natural gas, even if it also burns oil or other liquid fuel during periods of gas curtailment, startup or for periodic testing, not to exceed 48 hours during any calendar year.
  • Units with an Oxygen Trim System – Any boiler with an oxygen trim system that maintains an optimum air-to-fuel ratio.
  • Limited-Use – Any unit that burns any amount of solid, liquid or gaseous fuel and has a federally enforceable operating limit of less than or equal to 10 percent of an average annual capacity factor.

For a list of exceptions to the Major Source Rule, click here. 

Once you have determined your boiler’s size and fuel type go to  Step 3: Determine Compliance Requirements.

 

 

 

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