Custom / Other
Natural Gas
Fuel Oil #1
Fuel Oil #6
Bituminous Coal
Wood (Dry)
Mass of air required per unit mass of fuel.
Percentage of air supplied above stoichiometric requirement.
Standard density at 0°C (Air ≈ 1.293).
Calculation Results
Total Mass Flow Rate:–
Combustion Air Required:–
Normal Volumetric Flow (Nm³/hr):–
Actual Volumetric Flow (Am³/hr):–
*Nm³ is calculated at 0°C, 101.325 kPa. Am³ is calculated at the input Flue Gas Temperature.
function updateStoich() {
var fuelType = document.getElementById("fuelType").value;
var stoichInput = document.getElementById("stoichRatio");
// Approximate mass/mass stoichiometric ratios
if (fuelType === "natural_gas") {
stoichInput.value = 17.2;
} else if (fuelType === "fuel_oil_1") {
stoichInput.value = 14.6;
} else if (fuelType === "fuel_oil_6") {
stoichInput.value = 13.8;
} else if (fuelType === "bituminous_coal") {
stoichInput.value = 11.5;
} else if (fuelType === "wood") {
stoichInput.value = 6.4;
} else {
stoichInput.value = "";
}
}
function calculateFlueFlow() {
// Inputs
var fuelCons = parseFloat(document.getElementById("fuelConsumption").value);
var stoichRatio = parseFloat(document.getElementById("stoichRatio").value);
var excessAir = parseFloat(document.getElementById("excessAir").value);
var flueTemp = parseFloat(document.getElementById("flueTemp").value);
var density = parseFloat(document.getElementById("gasDensity").value);
// Validation
if (isNaN(fuelCons) || isNaN(stoichRatio) || isNaN(excessAir) || isNaN(flueTemp) || isNaN(density)) {
alert("Please fill in all numeric fields correctly.");
return;
}
if (fuelCons <= 0 || density <= 0) {
alert("Fuel consumption and density must be greater than zero.");
return;
}
// Logic
// 1. Calculate Mass of Air Required (including excess)
// Air Mass = Fuel Mass * StoichRatio * (1 + ExcessAir/100)
var airMassFlow = fuelCons * stoichRatio * (1 + (excessAir / 100));
// 2. Calculate Total Flue Gas Mass
// Mass Balance: Mass In = Mass Out (Fuel + Air = Flue Gas)
// Note: This neglects ash dropout for solid fuels, assuming all goes up stack for worst-case flow calc
var totalMassFlow = fuelCons + airMassFlow;
// 3. Calculate Normal Volumetric Flow (Nm3/hr)
// V = m / rho
var normalVolFlow = totalMassFlow / density;
// 4. Calculate Actual Volumetric Flow (Am3/hr)
// Using Ideal Gas Law correction for temperature: V2 = V1 * (T2/T1)
// T must be in Kelvin. T_std = 273.15 K (0°C)
var tempKelvin = flueTemp + 273.15;
var stdKelvin = 273.15;
var actualVolFlow = normalVolFlow * (tempKelvin / stdKelvin);
// Display Results
document.getElementById("resultsArea").style.display = "block";
// Formatting numbers
document.getElementById("resMassFlow").innerText = totalMassFlow.toLocaleString(undefined, {maximumFractionDigits: 1}) + " kg/hr";
document.getElementById("resAirFlow").innerText = airMassFlow.toLocaleString(undefined, {maximumFractionDigits: 1}) + " kg/hr";
document.getElementById("resNormalFlow").innerText = normalVolFlow.toLocaleString(undefined, {maximumFractionDigits: 1}) + " Nm³/hr";
document.getElementById("resActualFlow").innerText = actualVolFlow.toLocaleString(undefined, {maximumFractionDigits: 1}) + " Am³/hr";
}
How to Calculate Flue Gas Flow Rate
Calculating the flue gas flow rate is a critical step in the design and maintenance of industrial boilers, furnaces, and HVAC systems. Accurate flow rate data is essential for sizing stacks, selecting pollution control equipment (such as scrubbers or precipitators), and ensuring compliance with environmental emission standards.
The flue gas flow rate depends primarily on the type of fuel burned, the rate of fuel consumption, and the amount of excess air supplied to the combustion process to ensure complete burning. The calculator above provides a simplified mass-balance approach to estimate both mass and volumetric flow rates.
The Core Formula: Combustion Mass Balance
The fundamental principle behind calculating flue gas flow is the conservation of mass. The mass of the flue gas leaving the stack equals the sum of the mass of the fuel and the mass of the air entering the combustion chamber.
MassFlue Gas = MassFuel + MassTotal Air
Step 1: Determine Total Air Required
Combustion requires oxygen, which is supplied by air. Every fuel has a "Stoichiometric Ratio"—the exact amount of air required to chemically burn the fuel completely with no leftovers. However, in the real world, we add "Excess Air" to ensure the fuel burns cleanly without producing excessive carbon monoxide or soot.
The total air mass is calculated as:
MassAir = Fuel Rate × Stoichiometric Ratio × (1 + Excess Air %)
Example: Natural gas typically requires about 17.2 kg of air for every 1 kg of fuel. If you run 20% excess air, you multiply by 1.2.
Step 2: Calculate Volumetric Flow
While mass flow (kg/hr) is constant throughout the system, volumetric flow changes with temperature. Engineers distinguish between:
Normal Cubic Meters (Nm³/hr): The volume of the gas at Standard Temperature and Pressure (usually 0°C and 1 atm).
Actual Cubic Meters (Am³/hr): The volume of the gas at the actual stack temperature.
Hotter gases expand and take up more space. We convert Normal flow to Actual flow using the ratio of absolute temperatures (Kelvin):
QActual = QNormal × ((TStack + 273.15) / 273.15)
Typical Stoichiometric Air/Fuel Ratios
If you do not have a specific chemical analysis of your fuel, you can use these approximate mass-to-mass ratios for estimation:
Natural Gas: ~17.2 kg air / kg fuel
Fuel Oil (#1 or #2): ~14.6 kg air / kg fuel
Bituminous Coal: ~11.5 kg air / kg fuel
Dry Wood: ~6.4 kg air / kg fuel
Why Temperature Correction Matters
The difference between Normal and Actual flow is significant. A flue gas exiting at 200°C will occupy nearly twice the volume it would at standard conditions. Sizing a fan or duct based on Nm³ instead of Am³ would result in equipment that is severely undersized, leading to backpressure issues and poor combustion efficiency.