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Gas vs Propane Emissions Calculator - Side-by-Side CO2, NOx & SOx Comparison

Compare the environmental footprint of natural gas and propane for heating, process, and power generation

Compare emissions from natural gas and propane combustion side by side. Enter your annual energy consumption to see CO2, NOx, SOx, PM, CO, and VOC emissions for both fuels on an equivalent heat-input basis. Results show total tons per year, percentage difference, and cost-per-ton of emission reduction for fuel switching. Uses EPA AP-42 emission factors with adjustable control technology options.

Pro Tip: Natural gas emits about 117 lbs CO2/MMBtu while propane emits about 139 lbs CO2/MMBtu - roughly 19% more CO2 per unit of heat. But propane produces slightly less NOx and almost zero SOx. If your permit limit is NOx-driven, propane might actually be the better regulatory choice even though it produces more CO2. Always evaluate the pollutant that constrains your operations.

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Natural Gas vs Propane Emissions Calculator
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How It Works

  1. Enter Your Energy Consumption

    Input annual consumption in MMBtu, therms, MCF of gas, or gallons of propane. The calculator normalizes both fuels to equivalent heat input for a fair comparison.

  2. Select Equipment Type

    Choose boiler, furnace, water heater, or process heater. AP-42 emission factors vary by equipment type and size. The calculator applies the correct factor set for each fuel.

  3. Add Emission Controls

    Select any controls installed or planned: low-NOx burners, flue gas recirculation, or catalytic converters. Control efficiencies apply equally to both fuels for a fair comparison.

  4. Review Side-by-Side Results

    See pollutant-by-pollutant comparison showing which fuel produces less of each emission. Green highlights indicate the cleaner option for each pollutant.

  5. Evaluate Fuel Switching Economics

    Compare annual fuel cost difference against emission reduction to calculate cost per ton of CO2 or NOx reduced. Factor in any equipment conversion costs for payback analysis.

Built For

  • Facility managers evaluating fuel switching for emission reduction goals
  • Environmental staff comparing permit implications of natural gas vs propane
  • Rural facilities without natural gas access quantifying propane's emission profile
  • Corporate sustainability teams optimizing Scope 1 emissions across fuel types
  • Engineers designing new facilities choosing between gas and propane service
  • Energy consultants advising clients on lowest-emission fuel alternatives

Assumptions

  • Both fuels are compared on an equivalent heat-input basis (MMBtu).
  • Emission factors are EPA AP-42 averages for the selected equipment type.
  • Equipment operates at the same load and efficiency regardless of fuel type.
  • Fuel prices are user-entered and reflect delivered cost to the facility.
  • Control device performance is identical for both fuels when controls are selected.

Limitations

  • Does not account for equipment derating or efficiency differences between gas and propane burners.
  • Propane delivery logistics, storage tank costs, and supply reliability are not modeled.
  • Does not include upstream (Scope 2/3) emissions from fuel extraction, processing, or transport.
  • Equipment conversion costs are not factored into the economic comparison.
  • Regional fuel price volatility can change the cost comparison significantly over time.

References

  • EPA AP-42, Chapter 1.4 — Natural Gas Combustion emission factors.
  • EPA AP-42, Chapter 1.5 — Liquefied Petroleum Gas Combustion emission factors.
  • EPA Greenhouse Gas Equivalencies Calculator methodology.
  • EIA energy content values for natural gas (1,020 BTU/scf) and propane (91,500 BTU/gal).

Frequently Asked Questions

Propane produces approximately 19% more CO2 per MMBtu than natural gas. Natural gas emits about 117 lbs CO2/MMBtu while propane emits about 139 lbs CO2/MMBtu. However, propane appliances can sometimes achieve slightly higher thermal efficiency, which narrows the gap on a per-unit-of-useful-heat basis. For most applications, natural gas is the lower-carbon fossil fuel option.
NOx emissions are similar between natural gas and propane when burned in equivalent equipment. Natural gas typically produces 100-150 ppm NOx in uncontrolled boilers, while propane can be slightly lower at 90-130 ppm due to lower flame temperature. The difference is small enough that equipment design and burner type matter more than the fuel itself. Low-NOx burners reduce emissions by 30-50% on either fuel.
Propane is the primary choice for facilities without access to natural gas pipelines. It stores as a liquid in on-site tanks, requires no utility connection, and delivers more BTU per cubic foot than natural gas. Propane also has near-zero sulfur content, producing virtually no SOx emissions. For rural industrial sites, propane may be the lowest-emission fossil fuel option available.
1 therm of natural gas = 100,000 BTU = 1.09 gallons of propane (since propane has 91,500 BTU/gallon). To compare costs on an equal heat basis, divide the price per gallon of propane by 0.915 to get the equivalent price per therm. At $2.50/gallon propane and $1.50/therm gas, propane costs $2.73/therm equivalent - 82% more expensive for the same heat.
Yes. Switching fuels changes your emission profile and may require a permit modification. Even switching from propane to natural gas (typically a reduction) should be reported to your permitting authority. If switching increases any pollutant, you may need a construction permit or permit amendment before making the change. Some permits include fuel-specific emission limits that must be updated.
Disclaimer: This calculator uses EPA AP-42 emission factors for natural gas and propane comparison. Actual emissions depend on equipment type, condition, and operating parameters. Fuel cost comparisons use user-entered prices and do not account for equipment conversion costs or supply reliability. Consult your permitting authority before making fuel changes that could affect your air permit.

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