stack height requirements (stack height norms)
Also known as: chimney height requirement · exhaust stack height
Stack height requirements are the mandatory minimum heights that CPCB sets for the exhaust stacks of diesel generators and other combustion equipment, so that emissions disperse high enough to protect ground-level air quality. They are enforced as a condition of the plant's consent.
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What is stack height requirements?
Stack height requirements are the minimum chimney or exhaust heights mandated for combustion sources — diesel generator sets, boilers, thermal oxidisers, pyrolysis flue stacks — so that the emitted gases are released high enough to disperse and dilute before reaching ground level. A taller stack carries the plume further from people and lets wind dilute pollutants, lowering the ground-level concentration of the emissions even when the total mass emitted is unchanged. Stack height is therefore a dispersion control, working alongside, not instead of, emission limits.
In India the CPCB specifies stack heights for DG sets on a sliding scale tied to the set's capacity (in kVA), with a commonly used formula-based minimum and a stated minimum height above the building or ground. Larger sets require taller stacks. For process emission sources the stack height is set in the consent conditions, often referencing the surrounding building heights so the plume clears the roofline and does not create a ground-level pollution pocket. These requirements sit within the broader air-pollution framework (the Air (Prevention and Control of Pollution) Act, 1981 and the ambient air quality standards) administered by the SPCBs.
The requirement matters because an undersized stack can cause a plant to fail ground-level ambient air quality even when its emission concentrations at the stack are within limits — the pollutants simply do not disperse and accumulate near the boundary, triggering complaints and notices. It can also re-entrain exhaust into the plant's own air intakes. Getting stack height wrong is a common and avoidable consent non-compliance.
For an Indian entrepreneur the guidance is to confirm the required stack height for each combustion source against the applicable CPCB norm and the consent conditions before fabrication, taking into account the kVA of each DG set and the height of surrounding buildings. Build to the specified height (do not shorten stacks to save cost or for aesthetics), and verify the as-built heights are documented in the consent file. Where stacks serve emission sources, pair the correct height with the required monitoring so both the dispersion and the concentration sides of compliance are covered.
Common questions about stack height requirements
Plain-English answers to what people most often ask.
What are stack height requirements?
How is DG set stack height decided in India?
Why does stack height matter for compliance?
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