FD fans sit on the clean side of the combustion process — pushing ambient or pre-heated air into boilers, fired heaters, kilns and burners at controlled pressure. Cleaner duty than ID, but the engineering bar is just as high: efficiency wins or loses operating cost, the curve must stay pressure-stable across turndown, and sound matters when the fan sits beside personnel. We build FD fans across the full envelope below — up to 2,00,000 CMH, 2,000 mmWC and 400 HP.
A Forced Draft fan sits upstream of the burner: pushing ambient or pre-heated combustion air into the furnace, holding positive pressure on the burner side, and delivering it stable enough for clean, steady flame across the whole load range.
Combustion air into the furnace, holding positive pressure on the burner side — in a balanced-draft boiler the chamber is held slightly negative, typically −5 to −10 mmWC.
Pressure stable across the operating range. Burners need consistent air for stable flame and emissions — so we size onto the falling portion of the curve, typically 5–15% right of the peak.
Ambient or pre-heated air, not flue gas — to 350 °C downstream of an air pre-heater. Wear protection is rarely needed; the focus shifts to efficiency, curve shape and noise.
Clean air does not make the duty easy. Efficiency sets the lifetime electricity bill, the curve must stay stable under burner back-pressure swings, and sound matters when the fan sits beside people. A 200 HP FD fan run several points below its best static efficiency wastes tens of MWh a year — over a 20-year life the efficiency choice can outweigh the original CAPEX.
FD fans run continuously at high power. At 8,000 h/yr, a 200 HP fan held a few points below its achievable efficiency burns money every hour it runs.
How we engineer it outBackward-curved / backward-inclined wheels for high static efficiency on standard duty; airfoil-bladed impellers for higher on airfoil high-efficiency builds where the operating hours justify the CAPEX.
Sized onto the flat or rising part of its pressure–flow curve, an FD fan can stall under back-pressure swings, oscillating the combustion-air supply and disrupting flame.
How we engineer it outWe engineer the duty point onto the falling portion of the curve — typically 5–15% right of the peak — for inherent stability, then prove the curve on the rig.
FD fans often sit in equipment rooms or next to operator stations, where blade-pass and low-frequency content carry into occupied space.
How we engineer it outDesigned to <85 dB(A) @ 1 m as standard; <80 dB(A) with inlet/outlet silencers and acoustic-treated casing; <75 dB(A) with a custom acoustic enclosure.
We don't sell a catalogue near-fit. The fan is engineered to your air temperature, pressure rise, turndown range and sound limit.
No catalogue fan forced onto your spec. Your operating point is engineered onto the falling, stable portion of the selected wheel — 5–15% right of the peak — and verified on the 200 HP VFD test rig before dispatch.
| Parameter | Standard | On application |
|---|---|---|
| Volume flow | up to 2,00,000 CMH | higher on enquiry |
| Static pressure | up to 2,000 mmWC | higher on enquiry |
| Inlet air temperature | up to 350 °C (pre-heated air) | higher on application with special metallurgy |
| Static efficiency | high (backward-bladed) — figures shared on enquiry | higher on airfoil high-efficiency builds |
| Sound level | <85 dB(A) @ 1 m | <75 dB(A) with acoustic enclosure |
| Drive power | up to 400 HP | higher with custom motor sourcing |
| Speed | 600–1,800 RPM typical | per duty + sound limits |
| Balance quality | ISO 21940 G6.3 | G2.5 / G1.0 on application |
The envelope above covers the great majority of industrial FD-fan duty. For duty beyond it, we engineer to spec and quote on enquiry. Most FD fans handle clean ambient air, so wear protection is rarely required; inlet temperature only matters on pre-heated-air service downstream of an APH, where it can reach 200–350 °C. Bearing life is a design target of L10h ≥ 40,000 h continuous, with longer L10 on application.
The same engineering language carries from your enquiry to the GA drawing to the nameplate — expressed in the standard AMCA conventions.
| Specification field | Options |
|---|---|
| Arrangement (AMCA 99) | Arr. 1 (overhung, fan bearings) / Arr. 4 (direct, motor on base) / Arr. 8 (overhung on common base) / Arr. 9 (overhung, motor side) / Arr. 10 (overhung, motor inside base) — selected by drive, access and temperature. |
| Width / inlet | SWSI (single width, single inlet) default for FD duty; DWDI (double width, double inlet) for high flow at moderate pressure. |
| Wheel type | Backward-curved or backward-inclined (default, best efficiency on clean air) / airfoil-bladed (highest-efficiency, large continuous-duty builds). |
| Class (by pressure / outlet velocity) | Class I / II / III selected from the duty point on the pressure-vs-outlet-velocity limits; higher class = heavier construction for higher pressure and tip speed. |
| Materials of construction | Mild steel + epoxy coating (standard) / stainless steel for humid coastal or corrosive chemical-plant air / IS 2062 or 16Mo3 casing for pre-heated air / aluminium impeller for ATEX Zone 2. |
| Drive | Direct-coupled / V-belt / VFD (default for turndown control). Drive up to 400 HP across the envelope; speed typically 600–1,800 RPM. |
| Discharge & rotation (AMCA orientation) | Rotation CW or CCW (viewed from drive side) with discharge angle per AMCA — e.g. TH/BH/UB/DB — set to match your duct take-off and installed footprint. |
| Accessories & acoustic scope | Inlet vane damper or VFD control; inlet silencer (cylindrical or splitter-type) for low-frequency content; outlet silencer and casing-wall acoustic lagging; acoustic enclosure for <75 dB(A); expansion joints and thermal scope for pre-heated-air service; drain and inspection doors. |
Every job's performance is verified at our works on the 200 HP VFD test rig, to the AMCA 210 / ISO 5801 method, before dispatch.
Utility boiler FD, cogen FD, industrial steam-boiler FD.
Kiln main-burner FD, calciner FD, raw-mill bag-house FD.
Reheating-furnace combustion air, blast-furnace stove blowers.
Process-boiler FD; fired-heater FD (the heater is API 560, the FD fan serving it is API 673).
Refinery fired-heater FD fans.
Drying-furnace and roaster FD fans.
Boiler FD for utility steam.
45 application/duty types engineered. Tell us yours.
What our marks mean, in the words that survive an audit.
Tested to the AMCA 210 / ISO 5801 method, in-house on our 200 HP VFD rig. Tested-to-method — not AMCA-certified.
ISO 9001:2015 — third-party certified. Our only third-party certification.
Self-declared per 2006/42/EC + 2014/35/EU (Module A). A self-declaration, not a notified-body certificate.
Self-declared, Zone 2/22, Category 3, per 2014/34/EU, where the area classification calls for it.
Designed and built to API 673 as project-specific scope.
ASME Sec IX qualified welders + WPS for every joint.
ISO 21940 — G6.3 minimum, G2.5 / G1.0 on application.
ISO 20816 evaluation; ISO 14694 for fan-specific limits.
| Stage | Standard duty | API-673 / engineered |
|---|---|---|
| Offer / quotation | 3 working days — always | 7–10 working days |
| GA drawing for approval | 2–3 weeks from PO | 3–4 weeks from PO |
| Manufacture + balance + paint | 6–10 weeks | 10–14 weeks |
| Performance test + witnessed FAT | ~1 week | 1–2 weeks |
| Order-to-dispatch (total) | 9–14 weeks | 14–20 weeks |
Shutdown-driven replacements: we have shipped fans within 6 weeks of a clean PO. Tell us your shutdown window and we commit to a dated plan.
The same engineering, viewed three ways — by fan family, by duty, and by industry. Follow the cross-references.
No model numbers needed. Give us the operating conditions — flow, static, gas temperature, composition, particulate, and any tender standard — and our application engineers size the fan and quote it. Attach a spec or GA if you have one.
+91 90110 09155 · mihir.jitamitra@gmail.com