What does EnerTherm Engineering do?

EnerTherm Engineering is a UK-based industrial engineering company that designs and delivers thermal process solutions, energy auditing services, and bespoke thermal equipment for manufacturing and process industries. Services include energy audits, pinch analysis, process modelling, thermal design simulation, and project management.

What thermal products does EnerTherm Engineering manufacture?

EnerTherm Engineering manufactures process heaters, heat exchangers, thermal oxidisers, incinerators, condensers, dehydrators, and the Omni Vision industrial energy intelligence platform. All products are custom-designed for specific industrial applications and process requirements.

Does EnerTherm Engineering provide energy auditing services?

Yes. EnerTherm Engineering provides comprehensive energy audits, heat loss audits, and pinch analysis to identify energy waste, quantify potential savings, and prioritise capital investments in industrial facilities across sectors including chemical, pharmaceutical, food & beverage, and manufacturing.

What industries does EnerTherm Engineering serve?

EnerTherm Engineering serves chemical processing, pharmaceutical, food & beverage, oil & gas, power generation, automotive, textile, paper & pulp, general manufacturing, waste management, agriculture, healthcare, and mining & metals industries.

Where is EnerTherm Engineering located?

EnerTherm Engineering is headquartered in the United Kingdom and provides engineering services and thermal equipment to clients internationally.

Can EnerTherm Engineering help with industrial decarbonisation?

Yes. EnerTherm Engineering specialises in waste heat recovery system design, process optimisation for energy reduction, and net zero carbon roadmapping. They also provide ISO 14001 and ISO 50001 compliant energy management strategies.

does EnerTherm Engineering offer CFD simulation and thermal modelling?

Yes. EnerTherm Engineering provides Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) for thermal equipment design. These simulations validate heat transfer performance before fabrication, reducing costly physical prototyping.

What is a thermal oxidiser and does EnerTherm Engineering supply them?

A thermal oxidiser is an industrial system that destroys volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) through controlled high-temperature combustion. EnerTherm Engineering designs and manufactures regenerative, recuperative, and direct-fired thermal oxidisers for chemical, pharmaceutical, and manufacturing industries.

Does EnerTherm Engineering design custom process equipment?

Yes. EnerTherm Engineering provides bespoke engineering design of process vessels, heat exchangers, reactors, and thermal treatment systems from concept through to fabrication-ready drawings, as well as rapid prototyping and pilot plant commissioning.

What is EnerTherm Engineering's Omni Vision platform?

Omni Vision is EnerTherm Engineering's industrial energy intelligence platform. It provides turnkey utility metering, CO2 tracking, and AI-powered production KPI intelligence for industrial compliance monitoring and operational optimisation.

[Combustion Systems]

Free tool

Combustion Air & Flue Gas Calculator

Calculate the required combustion air flow rate and resulting flue gas production for industrial combustion systems using metric units.

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Built by our engineers

Part of EnerTherm's free calculator suite — the same methods we use on live industrial projects.

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[CALCULATOR]

Fuel

Fuel preset

Composition (mol %)

Normalised to 100% internally, so a total slightly off changes the proportions, not the result.

CH₄

C₂H₆

C₃H₈

C₄H₁₀

CO₂

N₂

Σ = 100.00 % — totals 100% ✓

Fuel flow rate (Nm³/h)

Combustion air

Specify air by

Excess air %Air ratio λMeasured O₂Measured CO₂

Excess air %

Air temp °C

Air RH %

Flue temp °C

SO₃ conv. %

CO (incomplete) %

Flue temp sets the temperature at which flue-gas properties (cp, density) are evaluated. SO₃ conversion drives the acid dew point.

Fuel properties

Molar mass17.277 g/mol

HHV52.22 MJ/kg

LHV47.12 MJ/kg

HHV (vol)40.25 MJ/Nm³

LHV (vol)36.32 MJ/Nm³

Stoich AFR16.22 kg/kg

Stoich air9.67 Nm³/Nm³

CO₂max (dry)11.94 %

Wobbe index52.1 MJ/Nm³

Rel. density0.596

Results

Thermal input

10,090kW (LHV)

Flue-gas flow

12,151Nm³/h wet

Excess air

15.0% (λ 1.15)

O₂ dry

2.99%

CO₂ dry

10.24%

Flue mean cp

1.110kJ/kg·K

Water dew pt

56.2°C

Acid dew pt

—no S

Flame temp

1,816°C equil.

Flame temp is the equilibrium adiabatic value with dissociation — the realistic peak. Frozen (no-dissociation) upper bound: 1,847 °C. Equilibrium flame NO ≈ 3,112 ppm (peak; kinetically frozen downstream — indicative only). Flame temp is informational and does not affect the flow results.

Flue-gas composition

Species	Wet mol %	Dry mol %	Mass %
CO₂	8.554	10.238	13.475
H₂O	16.451	—	10.608
N₂	71.642	85.749	71.835
O₂	2.502	2.994	2.865
Ar	0.851	1.019	1.217
Total	100.00	100.00	100.00

Wet includes water vapour; dry excludes it (renormalised). Mass % on the wet basis.

Dew points & materials

Water dew point56.2 °C

H₂SO₄ dew point— (no sulphur)

SO₃ conversion—

Safe metal temp≥ 66 °C

No sulphur in the fuel — acid dew point does not apply. Keep surfaces above the water dew point for a non-condensing design.

Flue-gas properties

Thermal input (LHV)10,090 kW

Thermal input (HHV)11,180 kW

Flue-gas flow (wet)12,151 Nm³/h

Flue-gas flow (dry)10,152 Nm³/h

Flue-gas mass flow15,146 kg/h

Combustion air11,124 Nm³/h

MW wet27.938 g/mol

MW dry29.892 g/mol

Density (0°C, wet)1.2465 kg/Nm³

Density @200°C0.7196 kg/m³

cp @200°C1.131 kJ/kg·K

Mean cp (→25°C)1.110 kJ/kg·K

Flue gas (wet)0.272 Nm³

Flue gas (mass)0.339 kg

Air moisture0.00 mol/kmol air

H₂O partial p16.67 kPa

[READ_THE_NUMBERS]

Results are indicative

Figures assume typical conditions and the stated method. For measured, guaranteed numbers on your plant, our engineers run site surveys, heat loss audits, and full process models.

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Send us the result — we'll tell you what it means for your plant.

[ABOUT_THIS_TOOL]

Industrial Combustion Air & Flue Gas Estimation

This online tool is designed for plant engineers, boiler operators, and combustion system designers in the UK industrial sector. It provides rapid, accurate estimates of the combustion air required for stable burner operation and the resulting flue gas flow rates generated by the process. Accurately sizing these streams is critical for specifying forced-draft fans, induced-draft fans, ductwork, and stack dimensions, ensuring compliance with UK environmental and safety standards.

Governing Equations and Methodology

The calculator determines mass flow rates based on conservation of mass and the stoichiometric requirements of the selected fuel type. The total combustion air mass flow rate is calculated using the stoichiometric air-to-fuel ratio ( $A F R_{s t}$ ) and the operating excess air percentage:

\overset{m}{˙}_{ai r} = \overset{m}{˙}_{f u e l} \times A F R_{s t} \times (1 + \frac{Excess Air %}{100})

Assuming complete combustion, the total mass flow rate of the wet flue gas is the sum of the fuel mass input and the combustion air mass input:

\overset{m}{˙}_{f l u e} = \overset{m}{˙}_{f u e l} + \overset{m}{˙}_{ai r}

Inputs, Outputs, and System Assumptions

To perform the calculations, the tool requires the following inputs:

Fuel Type: Select from common industrial fuels (e.g., Natural Gas, Gas Oil, or Heavy Fuel Oil), which determines the default stoichiometric air-to-fuel ratio.
Fuel Flow Rate: The mass flow rate of the fuel input, entered in kilograms per hour ( $kg/h$ ).
Excess Air Percentage: The percentage of air supplied above the theoretical stoichiometric requirement (%).

The tool returns the following outputs:

Combustion Air Mass Flow Rate: The required mass flow of air in kilograms per hour ( $kg/h$ ).
Flue Gas Mass Flow Rate: The total mass flow of combustion products in kilograms per hour ( $kg/h$ ).

Calculations assume complete combustion with zero unburnt carbon, standard atmospheric air composition, and nominal stoichiometric ratios (e.g., $17.2 kg_{air} / kg_{fuel}$ for standard UK natural gas).

Worked Industrial Example

Consider an industrial package boiler operating in a UK food processing plant burning natural gas at a rate of $250 kg/h$ with an excess air level of $15%$ .

First, the combustion air mass flow rate is calculated using the stoichiometric ratio of $17.2 kg_{air} / kg_{fuel}$ :

\overset{m}{˙}_{ai r} = 250 kg/h \times 17.2 \times (1 + \frac{15}{100})

\overset{m}{˙}_{ai r} = 4945 kg/h

Next, the total wet flue gas mass flow rate is determined by adding the fuel mass flow to the air mass flow:

\overset{m}{˙}_{f l u e} = 250 kg/h + 4945 kg/h

\overset{m}{˙}_{f l u e} = 5195 kg/h

These mass flow rates can then be used by plant engineers to size the burner's combustion air fan and verify the carrying capacity of the existing exhaust stack.

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Frequently asked questions

Excess air is introduced to ensure complete combustion of the fuel, preventing the formation of hazardous carbon monoxide (CO) and soot. While stoichiometric combustion is theoretically perfect, real-world burners require extra oxygen to guarantee that every fuel molecule encounters sufficient oxygen within the combustion zone. However, excess air must be minimised to prevent thermal efficiency losses from heating unnecessary nitrogen.

Industrial natural gas burners typically operate with an excess air level of 10% to 20%, which corresponds to approximately 2% to 4% residual oxygen ($O_2$) in the dry flue gas. Modern low-NOx burners may require different excess air profiles to control flame temperatures and minimise thermal NOx formation. Operating below these levels risks incomplete combustion, while operating above them reduces boiler efficiency.

To convert the flue gas mass flow rate (kg/h) to an actual volumetric flow rate ($m^3/h$), you must divide the mass flow rate by the density of the flue gas at its actual operating temperature. Flue gas density decreases significantly as temperature increases, meaning volumetric flow rates at the stack are much higher than at standard conditions. This conversion is critical for correctly sizing exhaust ductwork, dampers, and induced-draft fans.

The stoichiometric air-to-fuel ratio is determined by the chemical composition of the fuel, specifically the ratio of carbon, hydrogen, and oxygen atoms. Natural gas, which is primarily methane, has a high hydrogen-to-carbon ratio and requires approximately 17.2 kg of air per kg of fuel. Heavy fuel oils contain more complex hydrocarbons and typically require less air per unit mass, averaging around 13.8 kg of air per kg of fuel.