1. Introduction
This manual provides comprehensive instructions for the safe and efficient installation, operation, and maintenance of your VENTS-US VK 125-5 Inch Centrifugal Inline Duct Fan. Please read this manual thoroughly before installation and use, and retain it for future reference. The VK 125 fan is designed for various ventilation applications requiring high static pressure and reliable air movement.
2. Safety Information
WARNING: To reduce the risk of fire, electric shock, or injury to persons, observe the following:
- Read all instructions before installing or servicing this fan.
- Installation work and electrical wiring must be done by qualified person(s) in accordance with all applicable codes and standards, including fire-rated construction codes.
- Sufficient air is needed for proper combustion and exhausting of gases through the flue (chimney) of fuel-burning equipment to prevent back-drafting. Follow the heating equipment manufacturer’s guideline and safety standards such as those published by the National Fire Protection Association (NFPA), and the American Society for Heating, Refrigeration and Air Conditioning Engineers (ASHRAE), and the local code authorities.
- When cutting or drilling into wall or ceiling, do not damage electrical wiring and other hidden utilities.
- Ducted fans must always be vented to the outdoors.
- Do not use this fan with any solid-state speed control device unless specifically approved for use with this fan.
- This unit has an ungrounded plug. To reduce the risk of electric shock, connect to properly grounded outlets only.
- Mount with the lowest moving parts at least 8 ft (2.5 meters) above floor or grade level.
3. Product Overview
The VENTS-US VK 125 is a 5-inch centrifugal inline duct fan designed for efficient air movement in demanding ventilation systems. Its robust construction and powerful motor ensure reliable performance.
Key Features:
- Airflow Capacity: Up to 235 CFM under 0" of static pressure, 214 CFM under 0.2" of static pressure.
- Motor: Quiet external rotor motor with thermal overload protection, consuming 114 W of power.
- Casing: Constructed from high-quality, UV-resistant plastic (flame rating - 5VA) for durability and corrosion resistance.
- Installation: Includes mounting brackets and a pre-wired power cord for quick and simple setup.
- Applications: Suitable for bathroom exhaust, kitchen ventilation, living areas, whole-house ventilation, duct boosting, workshops, and smoking areas.
- Safety & Quality: ETL listed and HVI certified for dependable, tested performance.

Figure 3.1: Front view of the VENTS-US VK 125 inline duct fan.

Figure 3.2: Side view of the VK 125 fan, showing mounting brackets and power cord.

Figure 3.3: View of the centrifugal impeller, designed for high static pressure applications.
Product Videos:
Video 3.1: A 360-degree view of the VENTS-US VK 125 inline duct fan, showcasing its design and components.
Video 3.2: Detailed product overview video for the VENTS-US VK series inline centrifugal duct fans, highlighting features and applications.
4. Specifications
Technical specifications for the VENTS-US VK 125 fan:
| Specification | Value |
|---|---|
| Brand | VENTS |
| Model Name | VK 125 |
| Size | 5" Centrifugal Duct Fan |
| Air Flow Capacity | 235 Cubic Feet Per Minute (CFM) |
| Wattage | 114 watts |
| Voltage | 120 Volts |
| Noise Level | 7 Sones |
| Product Dimensions | 8.69"D x 10.63"W x 9.81"H |
| Item Weight | 6.69 pounds |
| Finish Type | Plastic |
| Motor Type | Outrunner |
| Installation Type | Mounted |
| Indoor/Outdoor Usage | Indoor |
| Control Method | App (Note: Requires compatible external control system, not included) |
| Specification Met | UL 705 |

Figure 4.1: VK 125 Dimensions Diagram.
5. Installation
The VENTS-US VK 125 fan is designed for straightforward installation. Always ensure power is disconnected before beginning any installation work.
Installation Steps:
- Plan Placement: Determine the optimal location for the fan within your ducting system. The fan can be mounted at any angle and at any point along the duct run. Consider accessibility for future maintenance.
- Mounting: Use the included mounting brackets to secure the fan to a stable surface (e.g., ceiling joist, wall stud, or dedicated support structure). Ensure the fan is mounted securely to prevent vibration and noise. Refer to Figure 4.1 for dimensions and mounting points.
- Duct Connection: Connect the fan to your ductwork using appropriate duct clamps or aluminum tape to ensure airtight seals. The fan is compatible with 5-inch diameter ducts. Ensure the airflow direction arrow on the fan casing aligns with your desired ventilation path.
- Electrical Connection: The fan comes with a pre-wired power cord. Connect the fan to a standard 120V AC power outlet. Ensure the outlet is properly grounded. If hardwiring is required, consult a qualified electrician.
- Testing: Once installed, restore power and test the fan's operation. Check for proper airflow and listen for any unusual noises.
Note: For optimal performance and to prevent rain ingress, install the fan behind shutters if used in an exterior wall application.
6. Operation
The VENTS-US VK 125 fan operates by drawing air through one duct opening and expelling it through the other, creating a continuous airflow. Once properly installed and connected to power, the fan will operate when the power supply is active.
- Power On/Off: The fan's operation is controlled by the power switch or control system it is wired to.
- Airflow Direction: Ensure the fan is installed with the airflow direction arrow pointing towards the desired exhaust or supply path.
- Speed Control (Optional): If a compatible speed controller (not included) is installed, adjust the fan speed as needed for your ventilation requirements.
7. Maintenance
Regular maintenance ensures the longevity and efficient operation of your VENTS-US VK 125 fan. Always disconnect power before performing any maintenance.
Maintenance Schedule:
- Quarterly (or as needed): Inspect the fan impeller and housing for dust and debris buildup. Clean with a soft brush or cloth. Do not use harsh chemicals or abrasive materials.
- Annually: Check all electrical connections for tightness and signs of wear. Inspect duct connections for leaks and ensure they are securely sealed.
- Motor: The external rotor motor features long-life ball bearings and is designed to be maintenance-free. No lubrication is required.
If the fan requires repair, contact qualified service personnel. Do not attempt to repair the unit yourself.
8. Troubleshooting
If you experience issues with your VENTS-US VK 125 fan, refer to the following troubleshooting guide:
| Problem | Possible Cause | Solution |
|---|---|---|
| Fan does not operate | No power supply Loose electrical connection Thermal overload protection activated | Check power outlet and circuit breaker Verify all wiring connections (consult electrician if unsure) Allow fan to cool down; check for obstructions in airflow |
| Low airflow | Duct obstruction Leaky duct connections Fan impeller dirty | Inspect ductwork for blockages Seal all duct connections properly Clean the fan impeller (see Maintenance section) |
| Excessive noise or vibration | Loose mounting Impeller imbalance due to dirt Foreign object in fan housing | Ensure fan is securely mounted Clean impeller thoroughly Inspect fan for any foreign objects and remove them |
If the problem persists after attempting these solutions, contact VENTS-US customer support.
9. Warranty and Support
VENTS-US products are manufactured to high-quality standards and are backed by a manufacturer's warranty. Specific warranty terms and conditions may vary. Please refer to the warranty card included with your product or visit the official VENTS-US website for detailed information.
For technical support, service, or to inquire about replacement parts, please contact VENTS-US customer service through their official website or the contact information provided with your purchase documentation.





