Genset Stack Chimney: Design, Fabrication, Installation & AMC
CPCB-formula stack heights, MS / SS 304 / SS 316L fabrication, dispersion-aware DG room design, back-pressure compliant routing. Single vendor for site survey, fabrication, installation, certification and AMC across Bhiwadi, Delhi-NCR and Rajasthan.
Replacing a corroded MS stack? Adding a chimney after RPCB / HSPCB notice? We have done both this month.
I'm Here Because...
Pick your scenario and jump to the specific section that answers it.
New DG, need chimney design
Generator commissioning soon. You need an SPCB-compliant stack height, BOQ and indicative budget for the chimney along with foundation.
→ CPCB Stack Height CalculatorSPCB / RPCB notice for inadequate stack
You got a notice citing chimney height under CPCB formula. You need a corrective design, fast install and inspection-ready documentation.
→ Compliance & InspectionExisting MS stack rusting through
Visible corrosion, joint leaks, possibly hot spots on insulation. You need replacement (often with SS 304 / SS 316L).
→ Material Selection GuideMulti-DG plant, need shared stack
2-4 DGs at the same site. You want a multi-flue chimney, separate manifolds, common platform.
→ Stack ConfigurationsDG making excess back pressure
Higher EGT, derated load, black smoke. Existing stack has too many bends or wrong diameter. You need a back-pressure recalc and redesign.
→ Back Pressure & SizingJust budgeting, need indicative price
CFO/owner wants a ballpark for the next CAPEX cycle. You need ranges by stack height, material and kVA tier.
→ Indicative PricingCPCB Stack Height Formula (How Tall Should Your Chimney Be?)
CPCB and state PCBs require minimum stack height calculated as a function of DG capacity and tallest nearby building. Most enforcement notices in NCR are issued because the chimney was sized by eye, not by formula.
CPCB Formula (for DG sets > 800 kW)
H = 14 × (Q)0.3
Where H = stack height in metres above ground level
Q = SO2 emission rate in kg/hour (proxy via fuel sulphur and consumption)
For DG sets up to 800 kW: H = (height of building) + 6 m minimum, OR per state PCB notification (some states require + 8 m).
Quick Reference Table (Indicative Stack Heights)
| DG Capacity (kVA) | Typical Building (Roof Level) | Min. Stack Height Above Ground | Above Roof |
|---|---|---|---|
| Up to 62.5 kVA | 10 m (G+2) | 16 m | 6 m |
| 63 - 125 kVA | 10 m (G+2) | 17 m | 7 m |
| 126 - 250 kVA | 13 m (G+3) | 21 m | 8 m |
| 251 - 500 kVA | 15 m (G+4) | 24 m | 9 m |
| 501 - 1000 kVA | 18 m (G+5) | 28 m | 10 m |
| 1001 - 1500 kVA | 20 m (G+6) | 31 m | 11 m |
| 1501 - 2500 kVA | 25 m (G+7) | 35 m | 10-12 m |
These are illustrative minimums. State PCBs (RPCB, HSPCB, DPCC, UPPCB) may impose stricter requirements - especially in NCR's notified ozone-non-attainment zones. We verify against your specific PCB notification before fabrication.
Material Selection: MS vs. SS 304 vs. SS 316L
The single biggest cost driver. Pick wrong and you either overspend or have to replace the stack in 2-3 years.
| Material | Best Used For | Expected Life | Cost Index | Avoid If... |
|---|---|---|---|---|
| MS (Mild Steel) + heat-resistant paint | Standby DG < 250 kVA, low runtime, inland dry sites | 5-7 years | 1.0× (base) | Coastal site, > 8 hrs/day DG, dual-fuel DG (sulphur condensate) |
| SS 304 | Mid-size DG 125-500 kVA, regular weekly runs | 10-15 years | 2.2-2.6× MS | High-sulphur HSD area, condensate-prone site |
| SS 316L | Industrial DG > 500 kVA, prime/peak runtime, dual-fuel or gas DG, coastal / chemical zone | 15-25 years | 3.0-3.8× MS | Tight CAPEX and DG runs < 100 hrs/year |
| MS + SS 316L liner (composite) | Cost-balanced industrial use, mid runtime | 12-18 years | 2.0-2.4× MS | Tight headroom (composite wall thicker) |
| RCC or brick (industrial) | Multi-DG > 1500 kVA plants, > 30 m height | 25-40+ years | Quoted per project | Single small DG, retrofit on existing roof |
Stack Configurations We Fabricate
From single-DG vertical stacks to multi-DG common platforms with separate flues.
Free-standing on its own concrete foundation. No guy wires needed. Suited to single DG > 250 kVA where ground-level erection is possible.
Lighter wall, anchored via 3-4 sets of guy wires at calculated heights. Cost-effective for stacks 18-28 m on industrial roofs / open ground.
Tied to building structure via brackets and structural cradles. Common for rooftop DGs in NCR commercial complexes.
2-4 separate inner flues sharing an outer windshield. Used for multi-DG plants where each DG runs on its own duct but visually one stack is preferred.
Bracketed against a building wall. Used when rooftop space is constrained. Tower bracket spacing engineered for wind load.
Sections fabricated at workshop, bolt-joined at site. Reduces crane time and is preferred when site access is constrained (narrow lanes / no welding clearance).
Back Pressure: Why Your Stack Must Be Sized, Not Guessed
Excess exhaust back pressure derates the engine, raises EGT, increases fuel consumption and shortens turbo life. OEM limit is typically 75-100 mm WC (water column). A chimney too narrow or with too many bends silently destroys an engine.
- • Stack diameter smaller than engine exhaust manifold outlet
- • More than 3 bends (each 90° bend ≈ 5-7 m of straight pipe equivalent)
- • Long horizontal run before going vertical
- • Reducer / size step too sharp
- • Silencer below recommended size
- • Insulation damp / sagging (raises friction)
- • Bird mesh clogged with soot
- • Calculate exhaust gas mass flow from engine spec sheet
- • Pick stack ID to keep gas velocity 25-35 m/s at full load
- • Limit bends to 2 (3 max), use long-radius elbows only
- • Add expansion bellows after each long straight section
- • Pair silencer to engine residential / industrial spec
- • Verify total back pressure ≤ 75% of OEM limit (safety margin)
- • Provide back-pressure test point and gauge for AMC
Indicative Chimney Pricing (Market Reference)
First-cut market bands for CFO/PMC budgeting. Final commercial offer depends on stack height, material, bend count, foundation, structural design and site access.
| DG kVA Tier | Typical Stack Spec | MS + Paint | SS 304 | SS 316L |
|---|---|---|---|---|
| Up to 62.5 kVA | 100-150 mm ID, ~16 m, single bend | ₹35-55 K | ₹80 K-1.2 L | ₹1.1-1.6 L |
| 63-125 kVA | 150-200 mm ID, ~17 m | ₹55-90 K | ₹1.3-1.9 L | ₹1.7-2.5 L |
| 126-250 kVA | 200-250 mm ID, ~21 m, guy-wire or self-supported | ₹1.0-1.5 L | ₹2.2-3.0 L | ₹2.8-4.0 L |
| 251-500 kVA | 250-350 mm ID, ~24 m, self-supported | ₹1.8-2.8 L | ₹3.5-5.0 L | ₹4.5-6.5 L |
| 501-1000 kVA | 350-450 mm ID, ~28 m | ₹3.5-5.5 L | ₹6-9 L | ₹8-12 L |
| 1001-1500 kVA | 450-550 mm ID, ~31 m | ₹6-9 L | ₹10-14 L | ₹14-19 L |
| 1501-2500 kVA | 550-750 mm ID, ~35 m, may need multi-flue | ₹10-15 L | ₹16-24 L | ₹22-32 L |
Pricing includes: fabrication, transportation within 100 km of Bhiwadi, erection by certified team, insulation + cladding, foundation drawing, test certificate. Excludes: RCC foundation civil work, crane charges for > 25 m heights, structural cradle for building-supported variant, GST, and any PCB statutory fees.
Compliance, Documentation & PCB Inspection Pack
What CPCB and your state PCB will actually ask for during a Consent-to-Operate renewal or surprise inspection.
Stack height formula for > 800 kW; minimum dispersion height; provision for sampling port at 1.5×D from bend or 5×D from top.
RPCB, HSPCB, DPCC, UPPCB issue their own stack height notifications, some stricter than CPCB. Our design references the latest version at design date.
Commission for Air Quality Management notifications often raise stack and emission requirements during GRAP. Our design accounts for the higher of CPCB or CAQM applicable rules.
IS 6533:1989 = design of steel chimneys; IS 875:1987 = wind load code. All our structural calculations reference these.
Each OEM (Cummins, Greaves, Kirloskar, Mahindra, Volvo) publishes maximum allowable back pressure. We design for ≤ 75% of OEM limit to leave margin for fouling.
Threaded sampling port at calculated location with safe access ladder + platform. Without this, PCB inspector cannot draw a stack sample and your CTO renewal stalls.
Documentation Pack We Hand Over
- • Stack height calculation per CPCB / state PCB formula with annexed gazette reference
- • Wind-load and seismic calculation (IS 875 / IS 1893)
- • Material test certificate (MTC) for plate or pipe used
- • Welding NDT report (for site-welded joints > 10 mm thickness)
- • Back pressure calculation showing margin to OEM limit
- • Foundation drawing & reinforcement schedule
- • Lightning protection & aviation marking (if > 30 m)
- • Sampling port location drawing
- • Annual stack monitoring AMC log template
Chimney AMC: What Most People Skip Until A Notice Arrives
Stack maintenance is rarely scheduled until something fails. Three things kill a chimney early: condensate at the base, sagging insulation and over-tensioned guy wires.
Basic AMC
Annual visual + climbing inspection, structural integrity check, paint touch-up, bird mesh cleaning, condensate drain check.
Indicative: ₹18-30 K / year per stack
Standard AMC popular
Basic + half-yearly back pressure test, insulation/cladding check, guy-wire tension calibration, NDT spot-check on welds.
Indicative: ₹35-55 K / year per stack
Comprehensive AMC
Standard + minor patch / weld repairs + cladding sheet replacement + annual PCB sample drawing coordination + stack emission report support.
Indicative: ₹65-95 K / year per stack
Where We Have Installed
Each occupancy type has its own constraints. Knowing them upfront saves redesign.
Manufacturing & RIICO Factories
Self-supported SS 304 / SS 316L stacks. Often combined with DG room canopy and fire pump installation.
Hospitals
Roof-mounted, super-silent silencer, SS 316L for proximity to oxygen plant and laboratory ventilation.
Hotels & Hospitality
Aesthetic concealment routing, internal duct insulation upgraded for sound, exterior cladding finish.
IT Park / Commercial High-Rise
Building-supported stacks routed via service shaft. Wind load + seismic checked per IS 1893 + IS 875.
Chemical & Pharma
Mandatory SS 316L. Sampling port and condensate trap engineered for sulphur capture.
Residential / Group Housing
Roof-mounted, residential silencer grade, lower stack height per CPCB < 800 kW rule (roof + 6 m).
Telecom Towers & Data Centres
Multi-DG common stack, knock-down design for tight access. Often dual-fuel DG which mandates SS 316L.
Logistics & Warehousing
Self-supported guy-wire stacks on independent foundations. Cost-effective for large warehouse perimeter DGs.
Related Services & Tools
Chimney sits inside the DG room compliance picture. Here is the rest of the stack.
Continue Exploring Alpha Diesels
Authorized Greaves Cotton (diesel generators) and Kirloskar Pneumatic (air compressors) dealer. 25+ years serving North India.
Equipment We Work With
Service Coverage Across Industrial Hubs
Frequently Asked Questions
Common questions about CPCB stack height, materials, pricing and AMC
Still Have Questions?
Our team is ready to help you with any queries
Get a Chimney Quote & Site Visit
Share your DG kVA, roof height, distance to nearest tall building and preferred material. We will revert with an indicative stack design, CPCB reference and a site visit slot.
Pricing on this page is indicative market range for first-cut budgeting only. Final commercial offer requires site visit, structural check and current state PCB notification verification.