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Fuel Combustion Emissions Calculator - EPA AP-42 Factors for CO2, NOx, SOx & PM

Calculate criteria pollutant and greenhouse gas emissions from natural gas, propane, diesel, oil & coal combustion

Free fuel combustion emissions calculator using EPA AP-42 emission factors. Enter fuel type and consumption rate to get annual emissions of carbon dioxide (CO2), nitrogen oxides (NOx), sulfur oxides (SOx), particulate matter (PM/PM10/PM2.5), carbon monoxide (CO), and volatile organic compounds (VOC) in tons per year. Supports natural gas, propane, No. 2 diesel, No. 6 fuel oil, bituminous coal, sub-bituminous coal, and biomass fuels. Results include both controlled and uncontrolled emission rates with major source threshold comparison for Title V and PSD applicability.

Pro Tip: AP-42 factors are averages - your actual emissions can vary by 50% or more depending on equipment age, maintenance, and operating conditions. If you are within 20% of a major source threshold, do not rely on AP-42 alone. Stack testing gives you site-specific factors that regulators will accept with far more confidence than handbook numbers.

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Fuel Combustion Emissions Calculator
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How It Works

  1. Select Your Fuel Type

    Choose from natural gas, propane, No. 2 distillate oil, No. 6 residual oil, bituminous coal, sub-bituminous coal, or biomass. AP-42 emission factors load automatically for each fuel.

  2. Enter Consumption Rate

    Input fuel usage in the unit that matches your records - therms, MMBtu, MCF, gallons, or tons depending on fuel type. The calculator converts everything to a common heat input basis.

  3. Specify Operating Hours and Controls

    Enter annual operating hours and select any emission controls in place (low-NOx burners, SCR, scrubbers, baghouse). Control efficiencies reduce the uncontrolled emission rates to actual permitted levels.

  4. Set Equipment Parameters

    Input boiler or heater rated capacity in MMBtu/hr. This determines whether your unit falls under NSPS Subpart Dc, Db, or Da and which AP-42 section applies.

  5. Review Emission Totals

    See annual emissions for each pollutant in tons per year, with color-coded indicators showing proximity to major source thresholds (100 tpy for attainment, 10/25 tpy for HAPs).

  6. Export for Permit Applications

    Copy the emission summary table for use in air permit applications, emission inventories, or annual compliance certifications.

Built For

  • Environmental managers preparing annual emission inventories for state agencies
  • Facility engineers evaluating major source applicability before adding new equipment
  • Consultants estimating emissions for air permit applications and PSD reviews
  • Plant operators tracking actual vs. permitted emission rates for compliance reporting
  • Energy managers comparing emission profiles of different fuel-switching scenarios
  • Corporate sustainability teams calculating Scope 1 greenhouse gas emissions

Frequently Asked Questions

AP-42 is the EPA's Compilation of Air Pollutant Emission Factors, containing average emission rates for hundreds of industrial processes. Chapter 1 covers external combustion sources like boilers, heaters, and furnaces. Factors are expressed in units like lb/MMBtu or lb/ton of fuel burned. AP-42 factors represent long-term averages and are rated A through E for data quality, with A being the most reliable.
Natural gas emits approximately 117 lbs of CO2 per MMBtu burned (AP-42 factor). For a boiler burning 50,000 therms/year: 50,000 therms × 0.1 MMBtu/therm = 5,000 MMBtu. Then 5,000 × 117 lbs/MMBtu = 585,000 lbs = 292.5 tons CO2/year. This is the most accurate simple method for Scope 1 GHG reporting.
Uncontrolled emissions are what the combustion process produces without any add-on pollution control equipment. Controlled emissions account for the reduction achieved by devices like low-NOx burners (30-50% NOx reduction), selective catalytic reduction or SCR (80-90% NOx reduction), scrubbers (80-95% SOx reduction), or baghouses (99%+ PM reduction). Permits typically set limits based on controlled emissions.
Under the Clean Air Act, a major source in an attainment area emits or has the potential to emit 100 tons per year of any single criteria pollutant. In nonattainment areas, thresholds drop to 10-100 tpy depending on severity. For hazardous air pollutants (HAPs), major source is 10 tpy of any single HAP or 25 tpy of combined HAPs. Exceeding these triggers Title V permitting and potentially PSD or NNSR review.
NOx formation depends on flame temperature, nitrogen content of the fuel, and combustion conditions. Natural gas burns cleanly and produces mostly thermal NOx (100-300 ppm uncontrolled). Coal and heavy oil contain fuel-bound nitrogen that converts to NOx during combustion, producing significantly higher rates. Equipment design matters too - a low-NOx burner on natural gas can achieve less than 30 ppm.
Most state agencies accept AP-42 factors for emission inventories and minor source permit applications. However, for major source permits, PSD applications, and MACT compliance, regulators often require site-specific stack testing or continuous emissions monitoring (CEMS). AP-42 factors carry more weight when the data quality rating is A or B. Always check your state's guidance on acceptable emission estimation methods.
Common conversions: 1 MCF natural gas = 1.02 MMBtu. 1 gallon No. 2 oil = 0.138 MMBtu. 1 ton bituminous coal ≈ 24 MMBtu (varies by coal grade). 1 gallon propane = 0.0913 MMBtu. To get lbs/year, multiply the emission factor (lb/MMBtu) by total annual heat input (MMBtu/year). Divide by 2,000 to convert to tons/year.
Disclaimer: This calculator uses EPA AP-42 emission factors for estimation purposes. Actual emissions depend on equipment design, operating conditions, fuel quality, and pollution control efficiency. AP-42 factors are averages and may not represent site-specific conditions. Always verify emission estimates against your air permit limits and consult your state environmental agency for regulatory compliance questions. ToolGrit is not responsible for permitting or compliance outcomes.

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