Shark BU3521
Shark Clean & Empty Cordless Stick Vacuum
Model: BU3521
Your comprehensive guide to operation and maintenance.
1. Product Overview
The Shark Clean & Empty Cordless Stick Vacuum is designed for versatile and convenient cleaning across various floor types. It features an innovative auto-empty system, lightweight maneuverability, and advanced filtration for a cleaner home environment.

Figure 1: Shark Clean & Empty Cordless Stick Vacuum with included accessories and auto-empty base.
2. Setup and Assembly
Before first use, ensure all components are present and the battery is fully charged.
2.1 Unboxing and Component Identification
- Cordless Vacuum Unit
- Auto-Empty Base
- PowerFins Multi-Surface Brushroll Nozzle
- 8" Duster Crevice Tool
- Pet Multi-Tool
- Removable DC-Jack Battery Pack
2.2 Assembly
- Insert the wand into the PowerFins Nozzle until it clicks securely.
- Insert the handheld vacuum into the top of the wand until it clicks.
- Place the assembled vacuum onto the Auto-Empty Base. Ensure it is properly seated for charging and emptying.

Figure 2: Proper assembly of the cordless vacuum components.
2.3 Initial Charging
Connect the Auto-Empty Base to a power outlet. Place the vacuum onto the base. The battery indicator lights on the vacuum unit will illuminate to show charging progress. A full charge takes approximately 5 hours. The vacuum is designed to be Always Charged and Always Ready when docked.

Figure 3: Vacuum docked on the auto-empty base for charging and automatic emptying.
3. Operating Instructions
3.1 Powering On and Selecting Cleaning Mode
To power on the vacuum, press the power button located on the top of the handheld unit. The redesigned LED display will show battery status and cleaning mode. You can cycle through three cleaning modes: ECO, AUTO, and BOOST, using the mode selection button.
- ECO Mode: Provides extended runtime for everyday cleaning.
- AUTO Mode: Automatically adjusts suction power and brushroll speed based on floor type for optimized cleaning.
- BOOST Mode: Delivers maximum suction for tough messes and deep cleaning.

Figure 4: Close-up of the LED display showing battery status and cleaning mode selection.
3.2 Multi-Surface Cleaning
The PowerFins multi-surface brushroll provides continuous cleaning contact, digging deep into carpets and directly engaging hard floors. In AUTO mode, the vacuum intelligently adjusts to different floor types.

Figure 5: The vacuum transitioning between carpet and hard floor, demonstrating multi-surface cleaning capability.
3.3 Using as a Handheld Vacuum
The vacuum easily transforms into a lightweight handheld unit for above-floor cleaning. Simply press the release button to detach the handheld vacuum from the wand.

Figure 6: Detaching the handheld vacuum unit for versatile cleaning.
3.4 Attaching Accessories
Attach the Duster Crevice Tool for cleaning hard-to-reach areas or the Pet Multi-Tool for removing pet hair and embedded dirt from upholstery and other surfaces.

Figure 7: Using the Duster Crevice Tool to clean narrow spaces.

Figure 8: The Pet Multi-Tool effectively removing pet hair from furniture.
3.5 LED Headlights
The powerful LED headlights on the nozzle illuminate hidden debris, making it easier to spot and clean dirt in dimly lit areas or under furniture.
4. Maintenance
4.1 Auto-Empty System Operation
The Shark Clean & Empty system automatically empties the vacuum's dust cup into the sealed base after every clean. This minimizes dust exposure and keeps your hands clean.

Figure 9: Illustration of the auto-empty system, showing debris transfer from vacuum to base.
4.2 Emptying the Auto-Empty Base
The auto-empty base has a larger capacity dust bin that requires less frequent emptying. When the bin is full, simply unclip it and dispose of the contents. The system is designed to lock away dirt, dust, allergens, and odors.
Video 1: Demonstration of the Shark Clean & Empty Cordless Stick Vacuum in use, showing its lightweight design and the automatic emptying feature when docked. The video highlights the ease of use and the self-emptying process into the base.
4.3 HEPA Filtration and Anti-Allergen Complete Seal
The system captures and traps over 99.97% of dust and allergens, ensuring cleaner air in your home. The Anti-Allergen Complete Seal technology prevents dust and allergens from escaping back into the air.

Figure 10: Visual representation of the HEPA filtration and Anti-Allergen Complete Seal system, highlighting its ability to trap dust and allergens.
4.4 Self-Cleaning Brushroll
The PowerFins brushroll is designed with self-cleaning technology to prevent hair wrap, making maintenance of the brushroll simple and hassle-free.

Figure 11: Comparison showing the effectiveness of the self-cleaning brushroll in preventing hair wrap.
4.5 Quiet Mode
The auto-empty base includes a Quiet Mode option, allowing you to dock and charge the vacuum silently, with the emptying process occurring at a later, more convenient time.
5. Troubleshooting
If you encounter any issues with your Shark Clean & Empty Cordless Stick Vacuum, please refer to the following common solutions:
- No Power/Not Charging: Ensure the power cord is securely plugged into the wall outlet and the auto-empty base. Verify the vacuum is correctly seated on the charging dock. Check the battery pack for proper insertion.
- Reduced Suction: Check the dust cup and auto-empty base for fullness and empty if necessary. Inspect the brushroll for any obstructions or tangled hair. Ensure all connections (nozzle to wand, wand to handheld) are secure. Clean the HEPA filter as per maintenance instructions.
- Brushroll Not Spinning: Check for clogs in the nozzle or wand. Ensure the brushroll is free from obstructions.
- Auto-Empty Not Working: Ensure the vacuum is properly docked and the base is powered on. Check the base's dust bin for fullness.
For more detailed troubleshooting or persistent issues, please visit the official Shark support website or contact customer service.
6. Specifications
| Feature | Specification |
|---|---|
| Brand | Shark |
| Model Name | Clean & Empty |
| Model Number | BU3521 |
| Special Feature | Spotless Cleaning, High Precision Sensors, Lightweight, Cordless, HEPA |
| Filter Type | HEPA Filter |
| Capacity | 1.3 Liters (Auto-Empty Base) |
| Runtime | Up to 40 minutes (in ECO mode, measured at hand vacuum) |
| Charging Time | 5 Hours |
| Power | 180 watts, 25 Amps |
| Battery Type | Lithium-Ion |
| Item Weight | 11.24 pounds |
| Product Dimensions | 14.69"L x 10.43"W x 43.5"H |
7. Warranty and Support
For warranty information, product registration, and customer support, please visit the official SharkNinja website or refer to the warranty card included with your product. Online resources often include FAQs, troubleshooting guides, and replacement part ordering.
You can find more information and support at www.sharkclean.com.
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