Skip to main content
Emissions Free Pro Features Available

Stack Flow & Mass Emissions Calculator

Convert stack test measurements to standardized flow rates and annual emission totals

Free stack flow and mass emissions calculator. Enter stack diameter, gas velocity or volumetric flow, temperature, moisture, and pollutant concentration to calculate dry standard cubic feet per minute (dscfm), O2-corrected concentrations, mass emission rates (lb/hr), and annual emissions (tpy). Supports ppm, mg/m3, and gr/dscf concentration units.

Pro Tip: When converting field measurements, always verify whether your O2 reading is on a wet or dry basis. Stack test labs usually report dry-basis O2, but some CEMS report wet-basis values. Using wet O2 in a dry-basis correction formula gives you a lower corrected concentration than reality. A 2% moisture difference can swing your mass rate by 3-5%.

Look up AP-42 emission factors for comparison

AP-42 Emission Factor Lookup →

Calculate control device efficiency from test data

Control Device Efficiency Calculator →

Check boiler efficiency and stack loss

Boiler Efficiency Calculator →

Calculate PTE from mass emission rates

PTE Calculator →

PREVIEW All Pro features are currently free for a limited time. No license key required.

Stack Flow & Mass Emissions Calculator
Pop Out

How It Works

  1. Enter Stack Dimensions

    Input the inside stack diameter in inches. The calculator determines the cross-sectional area.

  2. Enter Flow Conditions

    Provide either gas velocity (ft/sec) or volumetric flow rate (acfm). Enter stack gas temperature and pressure.

  3. Set Moisture and O2

    Enter the stack gas moisture content and measured O2 percentage. Select the appropriate O2 reference level for your source type (3% for boilers, 7% for incinerators, 15% for turbines).

  4. Enter Pollutant Concentration

    Input the measured concentration and select units. Choose the pollutant type to auto-fill molecular weight, or enter a custom value.

  5. Review Results

    Get standardized flow rate (dscfm), O2-corrected concentration, mass emission rate (lb/hr), and annualized emissions (tpy).

Built For

  • Stack test engineers converting field data to reportable emission rates
  • Air quality engineers preparing dispersion modeling inputs
  • Compliance managers verifying stack test reports from testing contractors
  • Permit writers checking emission rate calculations in permit applications
  • Plant engineers estimating emissions between formal stack tests

Assumptions

  • Gas behaves as an ideal gas (reasonable for stack conditions).
  • Standard conditions: 68F (528R), 29.92 inHg, dry basis.
  • Stack cross-section is circular and uniform at the measurement point.
  • Pollutant concentration and flow are uniform across the stack.

Limitations

  • Does not account for non-uniform velocity profiles (cyclonic flow, stratification).
  • Particulate matter mass rates from concentration data require isokinetic sampling verification.
  • Does not include EPA Method 19 F-factor based emission rate calculations.

References

  • EPA Method 1 - Sample and Velocity Traverses for Stationary Sources
  • EPA Method 2 - Determination of Stack Gas Velocity and Volumetric Flow Rate
  • EPA Method 4 - Determination of Moisture Content in Stack Gases
  • EPA Method 19 - Determination of Sulfur Dioxide Removal Efficiency and PM/SO2/NOx Emission Rates
  • 40 CFR Part 60, Appendix A - Reference Methods

Frequently Asked Questions

ACFM (actual cubic feet per minute) is the volumetric flow at actual stack conditions (temperature, pressure, moisture). DSCFM (dry standard cubic feet per minute) corrects to standard temperature (68F), standard pressure (29.92 inHg), and removes moisture. DSCFM is used for emission calculations because it provides a consistent basis for comparing measurements taken at different conditions.
Emission limits are often expressed at a reference O2 level (commonly 3% for boilers, 7% for incinerators, 15% for turbines). This prevents facilities from diluting stack gas with excess air to artificially lower concentrations. The correction formula adjusts the measured concentration to what it would be at the reference O2 level: Ccorr = Cmeas x (20.9 - O2ref) / (20.9 - O2meas).
NOx is conventionally reported as NO2 equivalent with a molecular weight of 46 g/mol. Even though most NOx at the stack is actually NO (MW 30), regulatory convention converts everything to NO2 for reporting purposes. The molecular weight matters for converting ppm concentrations to mass emission rates.
Disclaimer: This calculator performs standard thermodynamic conversions for stack flow and emission rate calculations. Results should be verified against EPA reference methods and applicable test protocols. Stack test data should be collected and reported by qualified testing firms following approved methods.

Learn More

Emissions

Control Device Selection Guide

Baghouse, ESP, scrubber, SCR, thermal oxidizer, carbon adsorber — how to select the right air pollution control device for your source and pollutant, plus cost-effectiveness analysis.

Read Guide →

Related Tools

Emissions Live

Fuel Combustion Emissions Calculator

Calculate CO2, NOx, SOx, and PM emissions from fuel combustion using EPA AP-42 emission factors. Supports natural gas, propane, diesel, fuel oil, and coal with annual emissions totals and cost-per-ton estimates.

Launch Tool →
Emissions Live

Refrigerant Leak CO2 Equivalent Calculator

Calculate CO2 equivalent emissions from refrigerant leaks using EPA GWP values. Supports R-410A, R-134a, R-22, R-404A, R-407C, R-32, R-1234yf, and more. See annual GHG inventory impact in metric tons CO2e.

Launch Tool →
Emissions Live

Boiler Efficiency & Stack Loss Calculator

Calculate boiler combustion efficiency from stack temperature and flue gas analysis. See stack heat loss, excess air percentage, and annual fuel savings from tuning. Supports natural gas and oil-fired boilers.

Launch Tool →