What single inlet, single width means
A SISW centrifugal arrangement receives air from one inlet side of the wheel. The casing and drive arrangement determine how the fan connects to the duct and where the motor and service components sit.
Single inlet does not mean low pressure or a small installation. The wheel design, size, speed and casing determine the performance. Use the actual curve at the required duty rather than assigning capability from the acronym.
A drawing should identify the inlet, outlet, rotation view and service envelope. Our rotation guide explains why the viewing side needs to be stated.
What double inlet, double width means
A DIDW arrangement receives air from both sides of a wider wheel arrangement. It can be useful where the equipment design provides an appropriate approach flow to both inlets.
Both inlet paths need consideration. A wall, motor arrangement or upstream component that restricts one side can affect the flow distribution. The available space must include the required clearances and service access, not just the casing width.
The wider arrangement does not guarantee twice the installed airflow. Performance depends on the model characteristic and the connected system resistance.
DIDW fan vs SISW fan: compare the design inputs
| Factor | SISW | DIDW |
|---|---|---|
| Inlet arrangement | One inlet side. | Two inlet sides. |
| Approach-flow review | Clearance and flow to that inlet. | Clearance and flow to both inlets. |
| Pressure and efficiency | Use the selected model’s curves. | Use the selected model’s curves. |
| Chemical suitability | Check all exposed components. | Check all exposed components. |
Compare the same airflow, pressure basis, air conditions and operating modes. A difference between two particular products should not become a universal claim about every single- or double-inlet fan.
Difference between SISW and DIDW fan layouts
Map the air path from the connected equipment into the fan. Identify bends, transitions, screens and structures that could distort the approach. The layout should allow the inlet conditions required by the manufacturer.
For a double-inlet arrangement, do not assess only the more accessible side. The hidden side needs an appropriate air path too. Include the installation and removal route, inspection space and access to the drive components.
Poor approach flow can create fan system effect. A compact layout that prevents the intended inlet conditions can undermine a sound catalogue selection.
Apply the comparison to chemical extraction
Review the extracted substances, temperature, possible deposits and cleaning method. Identify the wheel, casing, seals, shaft and motor arrangement against those conditions. Check the proposed materials against the contaminants and operating conditions.
Use the chemical exhaust fan guide to prepare that exposure list. For FumeCare’s equipment, the Fumeflow selection guide is the enquiry route.
Retain the accepted model, drawing and curve. Those details allow a future replacement to be compared with the intended duty and installed connections.
Questions about sisw vs didw fan
Does DIDW always deliver twice the airflow of SISW?
No. Compare the actual fan curves and system duty. Inlet arrangement alone does not determine installed airflow.
Is SISW the same as backward-curved?
No. SISW describes the inlet and width arrangement. Forward or backward curvature describes the blade geometry.