Put a dollar value on the opportunity

Estimate the fuel-cost difference.

Compare measured current combustion conditions with a proposed condition to screen the possible change in natural-gas use and annual fuel cost.

Measured-condition comparison

Compare current and proposed stack conditions.

Compare two measured operating conditions to screen how exhaust temperature and excess O₂ affect estimated stack loss, fuel use, and fuel cost. This is an engineering estimate, not an operating target.

Scenario inputs

Enter comparable burner-on conditions.

Excess O₂ measurement basis

Dry-basis O₂Excess O₂ (%)Wet-basis O₂Excess O₂ (%)

Many conditioned combustion analyzers remove moisture and report dry-basis oxygen. Instruments without moisture removal may report wet-basis oxygen. Select the basis for both excess-O₂ readings.

01 Current conditions

Current flue-gas temperature

°F

Stable measured exhaust temperature.

Combustion-air temperature

°F

Used for current and target conditions.

Current dry-basis excess O₂

% O₂

Enter the analyzer’s dry-basis oxygen reading.

Enter a reading to view converted values.

Utility billing unit

Use the same unit shown on the fuel bill.

Average current natural-gas usage

SCF/month

Use a representative operating period.

Natural-gas cost

$/1,000 SCF

Use the applicable commodity and delivery cost for screening.

02 Proposed comparison conditions

Target flue-gas temperature

°F

Enter a proposed comparison value. This is not a recommendation.

Target dry-basis excess O₂

% O₂

Enter the proposed dry-basis oxygen reading.

Enter a reading to view converted values.

The calculator opens with an illustrative industrial example. Its values are not an operating recommendation.

Screening estimate

Calculated change

Enter measured and target conditions, then calculate the comparison.

Estimated reduction

Estimated annual natural-gas reduction

—SCF/year

Estimated annual gas-cost reduction

—per year

Current calculated HHV stack efficiency: —
Target calculated HHV stack efficiency: —
Efficiency-point change: —
Estimated monthly target usage: —
Current equivalent dry excess O₂: —
Target equivalent dry excess O₂: —
Current calculated excess air: —
Target calculated excess air: —

Stack-loss breakdown

Energy lost through the stack, expressed as a percentage of the representative natural-gas higher heating value (HHV).

Loss component	Current % of fuel HHV	Target % of fuel HHV	Change percentage points
Dry flue gas	—	—	—
Water vapor	—	—	—
Total stack loss	—	—	—

Safety boundary

Overly aggressive air reduction can increase carbon monoxide, unburned fuel, instability, and safety risk. This calculator does not recommend an oxygen or excess-air setpoint. Qualified combustion personnel must confirm target conditions with appropriate safety testing.

What this estimate excludes

This screening estimate models stack losses for representative natural gas under steady-state, complete-combustion conditions. It does not include wall and opening losses, cooling losses, stored heat, product heat, burner cycling, production changes, air infiltration effects, carbon monoxide, unburned hydrocarbons, or equipment and installation costs. Results are not a combustion setpoint, engineering guarantee, or safety recommendation.

The model interprets measured oxygen as combustion excess air and cannot distinguish true burner excess air from downstream air infiltration.

Methodology and assumptions

What the model includes

Natural gas reacts with oxygen to produce carbon dioxide and water. Nitrogen and unused oxygen are heated and leave through the stack, while water produced by combustion leaves as vapor in a noncondensing system and carries substantial latent heat.

The calculator estimates dry-gas and water-vapor stack losses on a higher-heating-value basis. It does not calculate all furnace or process losses, so “stack efficiency” is intentionally narrower than overall furnace efficiency.

Representative natural-gas assumptions

Carbon mass fraction: 0.720
Hydrogen mass fraction: 0.238
Nitrogen mass fraction: 0.031
Oxygen mass fraction: 0.011
Higher heating value: 22,900 Btu/lb
Mean dry-gas heat capacity: 0.24 Btu/(lb·°F)

These published representative-fuel assumptions do not describe every utility gas supply exactly. Natural gas contains methane plus smaller amounts of other hydrocarbon and nonhydrocarbon compounds.

Billing conversions use 1 CCF = 100 SCF, 1 therm = 100,000 Btu, and 1 MMBtu = 1 Dth = 1,000,000 Btu. Converting an energy billing unit to SCF requires the utility gas heating value entered with the scenario.

Engineering references

Take the next step

Replace the example with a measured site assessment.

Share the equipment, operating profile, measurements, and fuel cost with our team. We can help define what should be measured before any investment decision.

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