Tools · Compliance
How tall must your DG exhaust stack be?
The CPCB formula, straight from the source document — enter the genset rating and building height, and get the minimum stack height your consent conditions will be measured against.
H = h + 0.2 × √kVA
H total stack height (m) · h height of the building where the set is installed (m) · kVA total generator capacity
Source: CPCB, Emission Regulations Part IV [COINDS/26/1986-87], as reproduced in CPCB's Environmental Standards compilation §22.0. Legal hook: Note 6, G.S.R. 771(E), 11 Dec 2013 — stack height for gensets "shall be governed as per CPCB guidelines."
The result is the CPCB minimum for genset engines up to 800 kW — State Pollution Control Board consent conditions can require more, and they prevail. Engines above 800 kW follow a different rule entirely (see the FAQ). Stack routing, supports, rain caps and condensate drains are fabrication engineering — we build those too.
The CPCB's own ready reckoner
| Generator set | Total stack height |
|---|---|
| Up to 50 kVA | Building height + 1.5 m |
| 50 – 100 kVA | Building height + 2.0 m |
| 100 – 150 kVA | Building height + 2.5 m |
| 150 – 200 kVA | Building height + 3.0 m |
| 200 – 250 kVA | Building height + 3.5 m |
| 250 – 300 kVA | Building height + 3.5 m |
Worked example
A 125 kVA set beside a 10 m building: H = 10 + 0.2 × √125 = 10 + 0.2 × 11.18 = 12.24 m — the stack must rise at least 2.24 m above the building. A 500 kVA set at the same site: H = 10 + 0.2 × 22.36 = 14.47 m.
Above 800 kW, the rules change
Engines above 800 kW fall under G.S.R. 489(E) (9 July 2002): the stack must be the maximum of 14 × Q0.3 metres (Q = SO₂ emission in kg/hr), 6 m above the building, or 30 m. That is fuel-chemistry territory, not a lookup — and it is exactly the regime under which we engineered and erected 30-metre stacks for the Reserve Bank of India.
Stack height, answered
Frequently asked questions
Is H = h + 0.2√kVA a law or a guideline?
It is a CPCB guideline — Emission Regulations Part IV (COINDS/26/1986-87) — but it carries legal force indirectly: Note 6 of G.S.R. 771(E) dated 11 December 2013 says stack height for gensets "shall be governed as per Central Pollution Control Board (CPCB) guidelines." State boards write it into consent conditions, which is where it becomes enforceable on your site.
Does the formula apply to very large DG sets?
Not above 800 kW engine rating. Those sets fall under G.S.R. 489(E) of 9 July 2002, where the stack must be the maximum of: 14 × Q^0.3 metres (Q = total SO₂ emission in kg/hr), 6 m above the building, or 30 m. That needs fuel and sulphur data, not just kVA — which is why this calculator stops at the ≤800 kW regime and why large installations (like the 30 m stacks we built for RBI) are engineered, not looked up.
Can my State Pollution Control Board demand more than the formula?
Yes. The CPCB figure is explicitly a minimum, and SPCB consent conditions or local requirements (CAQM in the NCR, for example) can and do impose stricter site-specific heights. Treat the calculator result as the floor you will never be allowed to go below — then confirm against your consent to operate.
My building is taller than 30 m — does the formula still hold?
Not on its own. For a small set on a tall building, 0.2√kVA can work out to barely a metre above the roof. Cummins’ installation bulletin (3243795) applies building height + 6 m as the minimum once the building exceeds 30 m — mirroring the "6 m above the building" term of the statutory >800 kW rule. The calculator applies that floor automatically and tells you when it has.
Is height the only exhaust dimension that matters?
No — diameter and routing matter as much, because they set exhaust back pressure. Practice is to size ducting for roughly 35–40 m/s gas velocity and keep a ~20% margin to the engine’s back-pressure limit; a single 90° elbow restricts like 5–8 m of straight pipe. For scale: V-engine sets run two exhaust lines into a Y after the silencers, and the common pipe is already 14 inch at 1000 kVA, growing to 18 inch at 2000 kVA. Exceed the back-pressure limit and the engine pays in fuel economy, exhaust temperature and life. That is fabrication engineering, not a formula — it is part of our exhaust stack scope.
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