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Roof Fans | DWT-I & DWT-II | YONGFAN
Building Envelope · Rooftop Exhaust

Roof Fans: Centrifugal vs. Axial for Building-Envelope Ventilation

Roof fans operate directly on the building envelope: they exhaust heat, moisture and stale air directly to the outside or pull from ducted risers without consuming internal floor space.

Compare YONGFAN DWT-I (centrifugal, 1,560 to 41,000 m³/h, 38 to 407 Pa static) and DWT-II (axial, 2,400 to 50,000 m³/h, 11 to 245 Pa static) roof fan families across airflow, static pressure, horizontal vs. vertical discharge, noise levels, and roof curb weather protection.

2 Key Series DWT-I Centrifugal · DWT-II Axial
Airflow Range 1,560 – 50,000 m³/h
Static Pressure 11 – 407 Pa Static
Weather Protection IP54 · Curb Cap · Backdraft Damper
Choose a Roof Fan Review Selection Principles
Industrial rooftop ventilation fan installation with weatherproof roof curb
Rooftop Aerodynamics Centrifugal (DWT-I) & Axial (DWT-II) · Weatherproof Envelopes
01 / Engineering Foundation

A Roof Fan is Both a Ventilation Device and a Roof Penetration

A roof fan must deliver required airflow against system resistance while withstanding wind loads, heavy rain, UV exposure, backdraft infiltration, and roof deck vibrations.

When air is exhausted through the roof, the fan is exposed directly to outdoor weather conditions. That creates engineering requirements that do not exist for an indoor in-line fan: weatherproof cowl design, reliable motor sealing (IP54 minimum), corrosion-resistant casing materials, gravity or motorized backdraft dampers to prevent cold air backdraft, and structural curb mounting that protects the roof waterproofing membrane.

Within this environment, the core aerodynamic question is whether the rooftop exhaust path is ducted (with substantial static pressure resistance from vertical risers, branch ducts, and dampers) or unducted / low-resistance (extracting directly from the open high-bay space beneath the roof deck).

YONGFAN solves both scenarios with the DWT Family: DWT-I provides centrifugal pressure capability (up to 407 Pa) with horizontal exhaust; DWT-II provides high-volume axial displacement (up to 50,000 m³/h) with vertical upward discharge.

Commercial rooftop exhaust fans and flashing curb
Rooftop curb flashing, gravity backdraft damper, and weather cap design.

Weatherproof Envelope Design

Spun aluminum or heavy FRP weather cap shields the motor and opening from torrential rain, driven snow, and intense solar UV radiation.

Protection: IP54 motor & seamless rain cowl

DWT-I: Ducted Static Pressure

Centrifugal impeller develops 38 to 407 Pa static pressure, overcoming multi-floor duct risers, bends, filters and branch balancing dampers.

DWT-I Duty: 1,560–41,000 m³/h · Up to 407 Pa

DWT-II: High Volumetric Flow

Axial impeller with adjustable pitch blades displaces massive heat and fume volumes (up to 50,000 m³/h) from open industrial high-bays.

DWT-II Duty: 2,400–50,000 m³/h · Up to 245 Pa

Discharge Plume Control

DWT-I discharges horizontally around the perimeter; DWT-II discharges vertically upward, projecting contaminated exhaust away from fresh air intakes.

Plume: Horizontal perimeter vs. Vertical jet

DWT Roof Fan Selection Rules

Determine whether your rooftop exhaust is ducted or free-inlet, then match required static pressure and discharge plume direction.

01 DWT-I: Centrifugal / Higher Static ΔP
02 DWT-II: Axial / Massive Free Flow
03 Vertical vs. Horizontal Plume
04 Curb Interface & Backdraft Damper
02 / Technical Metrics

DWT-I vs. DWT-II: Airflow, Static Pressure & Acoustic Comparison

Both families operate on published static pressure (ΔPs). Review the distinct operating ranges and sound performance before model sizing.
Spectrum 01 / DWT-I Centrifugal

DWT-I Performance Scope

1,560 to 41,000 m³/h airflow and 38 to 407 Pa static pressure across Ø300 to Ø900 mm diameters (No.3 to No.9). Motor powers range from 0.04 to 7.5 kW with noise levels from ≤52 to ≤81 dB(A).

Spectrum 02 / DWT-II Axial

DWT-II Performance Scope

2,400 to 50,000 m³/h airflow and 11 to 245 Pa static pressure across No.3 to No.10 (Ø300 to Ø1000 mm). Motor powers range from 0.04 to 5.5 kW with noise levels from ≤58 to ≤84 dB(A).

Spectrum 03 / Mechanical Envelope

Roof Curb & Damper Package

Pre-engineered curb mounting flanges, gravity-actuated backdraft dampers to eliminate wind driven infiltration, and protective bird/insect screens built standard.

Published Static Pressure (ΔPs) Comparison Across DWT Models

Both families are rated and published on a static pressure basis.

DWT Static Head Ranges
DWT-I Centrifugal Roof Fan
38 – 407 Pa Static
1,560–41,000 m³/h · Horizontal Discharge · ≤52–≤81 dB(A)
DWT-II Axial Roof Fan
11 – 245 Pa Static
2,400–50,000 m³/h · Vertical Discharge · ≤58–≤84 dB(A)
1. Exhaust Airflow m³/h capacity requirement
2. Static Pressure Pa duct loss vs. open roof
3. Fan Architecture Centrifugal (I) vs. Axial (II)
4. Curb & Damper Flashing dimension & backdraft
03 / Product Lineup

Choose the Roof Fan Family by Pressure and Discharge Direction

Detailed technical breakdown of DWT-I centrifugal and DWT-II axial roof fans.
Family 01 · DWT-I Centrifugal · Up to 407 Pa Static

DWT-I Centrifugal Roof Fan

The DWT-I Centrifugal Roof Fan is designed for rooftop exhaust systems with moderate to higher static pressure resistance resulting from duct networks, vertical risers, dampers, and filters.

Documented performance covers 1,560 to 41,000 m³/h airflow and 38 to 407 Pa static pressure across diameters from Ø300 to Ø900 mm (No.3 to No.9). It features a backward-curved centrifugal wheel, horizontal perimeter discharge cap (with upward discharge option available), and lower sound emissions from ≤52 to ≤81 dB(A). Ideal for commercial offices, institutional buildings, schools, and workshops with ducted exhaust.

Airflow & Static Pressure
1,560 – 41,000 m³/h · 38 – 407 Pa
Frame Sizes & Power
Ø300 – Ø900 mm (No.3–9) · 0.04 – 7.5 kW
Acoustic Profile
≤52 – ≤81 dB(A) sound pressure
Standard Discharge
Horizontal perimeter (upward optional)
Plume Separation Caution: If exhausting greasy kitchen fumes or toxic laboratory air, confirm whether horizontal discharge is acceptable under local building codes or if an upward high-velocity plume is required.
View DWT-I Product Details Request DWT-I Sizing
DWT-I Standard Frame Scope
DWT-I-No.3 ~ 4 Ø300 – Ø400 mm 1,560 – 4,200 m³/h
DWT-I-No.4.5 ~ 6 Ø450 – Ø600 mm 3,800 – 14,000 m³/h
DWT-I-No.7 ~ 8 Ø700 – Ø800 mm 12,000 – 28,000 m³/h
DWT-I-No.9 Ø900 mm 24,000 – 41,000 m³/h

*All models include curb base, rain cowl, bird screen, and IP54 motor.

Family 02 · DWT-II Axial · Up to 50,000 m³/h Flow

DWT-II Axial Roof Fan

The DWT-II Axial Roof Fan is the high-flow solution for industrial buildings, warehouses, manufacturing facilities, logistics centers, and large open-plan structures where high ventilation rates must be exhausted against low system resistance.

Published performance spans 2,400 to 50,000 m³/h airflow and 11 to 245 Pa static pressure across sizes from No.3 to No.10 (Ø300 to Ø1000 mm) with motor power from 0.04 to 5.5 kW. It features an axial impeller with adjustable-pitch aerofoil blades, standard vertical discharge blowing hot air away from the roof, and sound levels from ≤58 to ≤84 dB(A).

Airflow & Static Pressure
2,400 – 50,000 m³/h · 11 – 245 Pa
Frame Sizes & Power
No.3 – No.10 (Ø300–1000 mm) · 0.04 – 5.5 kW
Acoustic Profile
≤58 – ≤84 dB(A) sound level
Standard Discharge
Vertical upward discharge plume
Low-Resistance Duty Boundary: DWT-II is optimized for low-pressure environments (≤245 Pa). If significant ductwork or filtration is connected, static pressure drops can cause stalling; specify DWT-I instead.
View DWT-II Product Details Request DWT-II Sizing
DWT-II Standard Model Scope
DWT-II-No.3 ~ 4 Ø300 – Ø400 mm 2,400 – 5,500 m³/h
DWT-II-No.5 ~ 6 Ø500 – Ø600 mm 5,000 – 16,000 m³/h
DWT-II-No.7 ~ 8 Ø700 – Ø800 mm 14,000 – 32,000 m³/h
DWT-II-No.9 ~ 10 Ø900 – Ø1000 mm 28,000 – 50,000 m³/h

*Vertical discharge with gravity damper to prevent rain ingress.

04 / Selection Matrix

Roof Fan Family Routing & Comparison Table

Cross-reference YONGFAN DWT-I and DWT-II roof fans by application duty, documented aerodynamic boundary, and first technical input to confirm.
Product Family What It Solves Published Capability First Input to Confirm Specification Action
DWT-I Centrifugal Roof Fan Medium ΔP
Ducted or moderate-resistance rooftop exhaust with lower noise requirement
1,560–41,000 m³/h · 38–407 Pa Static · ≤52–≤81 dB(A)
 Required airflow, static pressure, and discharge direction Configure DWT-I
DWT-II Axial Roof Fan High Flow
High-flow, low-resistance roof exhaust in industrial halls & warehouses
2,400–50,000 m³/h · 11–245 Pa Static · ≤58–≤84 dB(A)
 Required airflow, building static resistance, and vertical plume clearance Configure DWT-II
Rule 01

Duct Resistance Criterion

If the fan connects to branch ductwork, risers or filters, choose DWT-I Centrifugal (up to 407 Pa). If unducted high-bay, choose DWT-II Axial.

Rule 02

Discharge Plume Strategy

DWT-I provides horizontal perimeter discharge. DWT-II provides vertical upward discharge projecting heat away from roof membranes.

Rule 03

Acoustic Boundaries

DWT-I operates at lower noise levels (≤52–≤81 dB(A)) suitable for commercial/institutional roofs near occupied areas or property boundaries.

Rule 04

Curb & Weather Flashing

Always verify roof curb dimensions, structural flashing interface, and gravity backdraft damper operation to eliminate air infiltration when idle.

05 / Procurement Protocol

Project Data Required for Roof Fan Selection

Provide design airflow, static pressure calculation, roof curb dimensions and discharge direction before requesting fan sizing.
STEP 01

Airflow & Static Pressure

Specify design airflow (m³/h) and calculated static pressure (Pa) including duct, riser, and curb losses.

STEP 02

Discharge Orientation

Choose horizontal perimeter discharge (DWT-I standard) or vertical upward discharge (DWT-II standard).

STEP 03

Curb & Weather Flashing

Confirm existing or planned roof curb dimensions (W×L×H mm), roof slope, and wind load rating.

STEP 04

Accessories & Electrical

Specify gravity backdraft damper, bird screen, isolator springs, 380V/50Hz supply, and noise limits.

Engineering Checklist

12 Parameters for Roof Fan Selection

Send your available project data. YONGFAN application engineers will verify aerodynamic operating curves, motor power margins, and curb dimension submittals.

1. Design Airflow (m³/h or CFM)
2. Required Static Pressure (Pa)
3. Ducted System vs. Open High-Bay
4. Operating Air Temperature (°C)
5. Discharge Direction (Horizontal / Vertical)
6. Roof Curb Dimensions (W×L×H mm)
7. Roof Pitch / Slope Angle
8. Ambient Wind & Weather Exposure
9. Noise Limit at Property Line (dB(A))
10. Power Supply (380 V / 50 Hz 3-Phase)
11. Backdraft Damper & Bird Screen
12. Normal Ventilation vs. Smoke Exhaust
06 / Manufacturing Consistency

YONGFAN Roof Fan Manufacturing & Weather Sealing Checks

FRP/spun aluminum cowl spinning, impeller dynamic balancing, weather sealing verification, and full electrical run-testing ensure durable rooftop operation.
Precision Fabrication

Impeller Dynamic Balancing

Centrifugal and axial rotating assemblies are dynamically balanced to ISO standards, preventing vibration transfer to building roof structures.

Weatherproof Testing

Water & Wind Ingress Checks

Rain cowl assemblies, gravity damper seals, and motor enclosure gaskets are tested to verify weather resistance under heavy wind-driven precipitation.

Motor Sealing

IP54 Sealed Motors

Weather-isolated motors with sealed bearings and corrosion-resistant hardware ensure reliable long-term outdoor operation without degradation.

Traceability

100% Inspection & Submittals

Final inspection covers curb flange dimensions, wiring boxes, cowl fasteners and packaging. Serial-number tracking and CAD curb details are provided.

Bespoke Project Engineering: Custom curb adapters, non-standard voltages, special anti-corrosive coatings, and upward discharge conversions available. Configured Dispatch: Lead times quoted based on model, frame size, motor build, quantity and project specifications.
07 / Engineering Knowledge

Roof Fans Frequently Asked Questions

Direct engineering answers regarding DWT-I vs DWT-II differences, discharge directions, backdraft prevention, and sound ratings.

What is the main difference between DWT-I and DWT-II?

DWT-I is a centrifugal roof fan for ducted or moderate-resistance systems (up to 407 Pa) with horizontal discharge and lower sound. DWT-II is an axial roof fan for high-flow, low-resistance industrial buildings (up to 50,000 m³/h) with vertical discharge.

Which YONGFAN roof fan provides higher pressure?

DWT-I provides the higher published static pressure envelope at 38–407 Pa. DWT-II operates from 11–245 Pa.

Which roof fan provides higher airflow?

DWT-II reaches 50,000 m³/h at frame size No.10. DWT-I reaches 41,000 m³/h at No.9.

Why does discharge direction matter on a roof?

Horizontal discharge (DWT-I) is compact and weather-tight for general ventilation. Vertical discharge (DWT-II) projects hot, humid or contaminated fumes high into the airstream, preventing re-entry into nearby HVAC outdoor air intakes.

How is rain prevented from entering through the roof fan?

Weather cowls shed precipitation away from the opening, and integrated gravity-actuated backdraft dampers close automatically when the fan shuts down.

What is the noise difference between DWT-I and DWT-II?

DWT-I is published at ≤52 to ≤81 dB(A), while DWT-II is published at ≤58 to ≤84 dB(A).

Can DWT roof fans be mounted on pitched roofs?

Yes, but an appropriately angled roof curb or transition base must be constructed to ensure the fan base sits level for proper bearing life and rain sealing.

What motor protection is standard on DWT fans?

Motors are IP54 rated for outdoor rooftop service, protected by the cowl enclosure and pre-wired with weatherproof terminal connections.

Can DWT fans handle emergency smoke exhaust?

Dedicated high-temperature fire-rated builds (e.g. 280 °C / 30 min) can be engineered and certified upon request; confirm fire duty in the project RFQ.

08 / Application Boundaries

Roof Fans Are Specialized Building Envelope Equipment

Specify a dedicated roof fan when discharging directly through the roof deck to eliminate plant-room floor space and avoid adapting indoor duct equipment to outdoor weather.
Boundary 01 / Indoor Ductwork

In-Line Duct Fans

If the fan sits inside a ceiling plenum or plant room before discharging through louvers, use DTF Axial or SWF Mixed-Flow.

Boundary 02 / Extreme Static Loss

Indoor Centrifugal Scrolls

If system resistance exceeds 407 Pa (complex multi-floor riser networks), locate a heavy-duty 4-72 Centrifugal Fan indoors.

Boundary 03 / Wall Exhaust

WEX Wall Fans

If exhausting horizontally through an exterior wall instead of penetrating the roof, use WEX / BWEX Wall Fans.

Boundary 04 / Hazardous Gas

Explosion-Proof Builds

If flammable vapor or combustible dust is present in the exhaust air, specify certified Explosion-Proof Ventilation Fans.

09 / Engineering Handoff

Select the Right Roof Fan for Your Building

You do not need to calculate rooftop static curves alone. Send your design airflow, calculated static pressure, roof structure details and weather exposure — our application engineers will confirm the optimal DWT-I or DWT-II model and provide complete curb submittals.

Design Airflow (m³/h / CFM) Static Pressure (Pa) DWT-I (Centrifugal) vs. DWT-II (Axial) Horizontal vs. Vertical Discharge Roof Curb Dimensions (W×L mm) Backdraft Damper & Bird Screen 380 V / 50 Hz 3-Phase
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HVAC application engineers reviewing rooftop fan equipment schedules
Direct Application Engineering Support
Static-pressure curve verification, curb flashing drawings, sound ratings & CAD/BIM submittals.
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