DG exhaust stack height: the CPCB formula, from the actual source

The minimum exhaust stack height for a diesel generator in India is the height of the building it sits beside plus 0.2 times the square root of its kVA rating: H = h + 0.2 × √kVA. A 125 kVA set at a 10 m building needs a 12.24 m stack; a 500 kVA set needs 14.47 m. That single formula settles most DG stack questions up to 800 kW — and above 800 kW a completely different rule takes over. Here is where each comes from, verbatim.

TL;DR

• Formula: H = h + 0.2√kVA — H is total stack height (m), h is building height (m)
• Source: CPCB guideline, Emission Regulations Part IV [COINDS/26/1986-87]
• Legal force: Note 6 of G.S.R. 771(E), 11 Dec 2013 — genset stack height “shall be governed as per CPCB guidelines”
• Engines above 800 kW: separate rule — max of 14×Q^0.3, 6 m above building, or 30 m
• The result is a minimum; your SPCB consent conditions can demand more, and they win
• Calculate yours here

Where the formula actually comes from

Ask three vendors for the source of the stack formula and you’ll get three vague answers. The paper trail is short once you actually pull it:

1. The formula appears in CPCB’s Environmental Standards compilation, section 22.0 “Diesel Generator Sets: Stack Height,” attributed by CPCB itself to Emission Regulations Part IV [COINDS/26/1986-87]. It is a CPCB guideline, not a numbered gazette rule — an important nuance.
2. The legal hook is Note 6 of G.S.R. 771(E), dated 11 December 2013 (the notification that set emission standards for diesel gensets up to 800 kW): “Stack height (in metres), for genset shall be governed as per Central Pollution Control Board (CPCB) guidelines.” That one sentence is what turns the guideline into an enforceable consent condition.
3. Your State Pollution Control Board writes it into your consent to operate — which is where it becomes your problem, and where a stricter site-specific figure can lawfully override the formula.

The CPCB’s own ready-reckoner

Alongside the formula, CPCB prints illustrative bands — useful for a quick sanity check:

For higher ratings, CPCB directs that the same formula be applied. Note what the bands quietly confirm: the increment above the roof is modest — 1.5 to 3.5 m for everything up to 300 kVA. The stack calculator applies the exact formula and draws the elevation for your inputs.

What changes above 800 kW

Engines rated above 800 kW are expressly excluded from the ≤800 kW regime and fall under G.S.R. 489(E), dated 9 July 2002, which prints its own stack rule for sets commissioned after 1 July 2003. The stack must be the maximum of:

• 14 × Q^0.3 metres, where Q is the plant’s total SO₂ emission in kg/hr,
• 6 m above the building where the set is installed,
• 30 m.

Notice the shift: kVA disappears entirely. The tall-stack requirement is driven by sulphur chemistry and dispersion, not electrical rating — which is why no honest online calculator can compute it from kVA alone, and why big-genset stacks are engineered projects with structural design, guying or self-support, aviation clearance where applicable, and crane logistics.

The case study: the six 1010 kVA sets we installed for the Reserve Bank of India at Belapur, Kharghar and Nagpur each sit under that >800 kW regime — delivered with 30-metre exhaust stacks, the floor the 2002 notification sets. The 2021–22 execution files still hold the crane records from the Nagpur lifts.

The mistakes we see on real sites

1. Measuring from the ground when the set is beside a building. The formula’s h is the building’s height; the stack must clear the roof by 0.2√kVA, not merely exist.
2. Treating the formula as a maximum. It is the minimum. If your consent letter says more, the consent letter wins.
3. Forgetting the stack when relocating a genset. Move a 250 kVA set from a ground-mounted yard (h = 0) to beside a 12 m building and the required stack grows by 12 metres.
4. Ignoring routing engineering. Backpressure limits, condensate drains, rain caps, expansion joints and supports are what make a stack survive — a pipe of the right height that chokes the engine is still a failed installation.

Getting it built

We fabricate and erect DG exhaust stacks as part of turnkey installation work — from a 3-metre roof extension on a retail set to the 30-metre RBI class. Send the genset rating and a photo of the site on WhatsApp, and you’ll get a straight answer on what your consent will require.

Sources: CPCB, Environmental Standards compilation §22.0 (formula, bands, COINDS/26/1986-87 attribution); G.S.R. 771(E) of 11 December 2013, Note 6 (legal hook, ≤800 kW); G.S.R. 489(E) of 9 July 2002 (>800 kW stack rule; Note 4 excludes ≤800 kW units). All documents verified in full — not quoted from secondary blogs. State consent conditions prevail over the formula minimum.