Start with your location and boiler rating. Dimensions update as you type.
Project location & height
Use a planning baseline or enter your approved height.
GPCB consent must be checked for your site. This is an indicative planning value, not a statutory minimum.
Your entered height is retained. The tool does not verify approval.
Boiler & fuel details
For a single boiler and its clear gas outlet.
Tonnes of steam per hour.
Leave blank to estimate fuel consumption from the steam/fuel ratio. Changing fuel resets consumption and fuel-specific assumptions.
Engineering assumptions & vendor data
Defaults are preliminary assumptions, not certified fuel properties. Workbook coal assumptions; fuel quality and excess air vary.
Total wet gas at stack exit temperature and pressure, not Nm³/s.
Applied to diameter, not flow.
View calculation breakdown
- Fuel mass flow
- 3,333.33 kg/h · Estimated from steam/fuel ratio
- Normalised dry gas flow
- 8.33 Nm³/s
- Normalised wet gas flow
- 9.47 Nm³/s
- Actual wet gas flow Q
- 15.71 m³/s
- Diameter before allowance
- 1.291 m
- Allowance and rounding
- 10% on diameter; round up to 0.05 m
Qₙ,dry = fuel × dry factor ÷ 3,600. Qₙ,wet = Qₙ,dry ÷ (1 − water fraction). Q = Qₙ,wet × (T + 273.15) ÷ 273.15 × 101.325 ÷ P. D = √(4Q ÷ πv). Normal conditions: 0°C, 101.325 kPa absolute.
- Statutory height is unverified. Emissions dispersion, nearby buildings, industry-specific rules and CTE/CTO conditions are outside this estimate.
- Gas flow uses preliminary fuel and water-vapour assumptions. Replace these with total wet gas flow from the boiler vendor for design.
- Exit velocity after allowance and rounding is below 10 m/s. Review draft and dispersion with the design engineer.
Your engineering summary
Enter your details to download the PDF. We also email you a copy.
Understand the estimate
From steam demand to chimney dimensions.
Choose the height basis
Enter your desired or consented height, or use an indicative regional baseline. A city selection identifies the location; it cannot establish statutory compliance.
Estimate the gas flow
Steam capacity and fuel assumptions estimate mass consumption. Dry gas volume, water vapour, temperature and pressure determine actual wet flow. Vendor flow can replace this estimate.
Size the clear outlet
The continuity equation Q = A × v gives the clear internal diameter. An explicit diameter allowance and upward rounding produce the preliminary result.
Questions before you start.
Is this a PCB-approved chimney height?
No. The 33 m Gujarat, 60 m Maharashtra and 70 m Karnataka values are requested planning baselines, not verified statewide mandates. Other states use a 30 m placeholder baseline. The latest project consent, industry rules, emissions and site context determine statutory requirements.
What does the calculated internal diameter mean?
It is the preliminary clear gas passage at the chimney outlet. It does not include lining, insulation, air gaps or RCC shell thickness. These need separate engineering design.
Can I use actual boiler vendor data?
Yes. Open Engineering assumptions & vendor data and enter actual total wet gas flow in m³/s at stack exit conditions. It bypasses the estimated fuel and gas factors.
Does it size the boiler or cover a common chimney?
Boiler TPH is an input; this tool does not select boiler capacity, size the ID fan or calculate a multi-boiler common stack. It estimates a chimney for one boiler. Common-stack arrangements require an engineering review.
Why are sulfur inputs not included?
The simplified tool does not calculate SO₂ dispersion height. A qualified engineer must assess emissions and statutory height separately. No default sulfur content or regulatory approval is assumed.
Method & reference notes
Fuel ratios and dry gas factors primarily follow BrajProjects’ RCC chimney height and ID calculation workbook. Lignite, moisture allowances and fuel-specific velocities are added planning assumptions and require engineering review. The BEE table provides combustion context; it does not certify this model.
- CPCB: general environmental standards ↗
- Bureau of Energy Efficiency: Guide Book 2, Energy Efficiency in Thermal Utilities, Chapter 2 (Boilers), Table 2.4
Model 1.0.0 · Reference review: 5 October 2026. No structural design, compliance approval or pricing is provided.