## Common ground
All options describe automated devices designed to clean swimming pools, typically using suction or mechanical scrubbing.
## Options at a glance
**8421.21 – Underwater-only cleaners**
- **Defining trait:** Designed exclusively for underwater operation; cannot function above water.
- **Typical examples:** Submersible pool scrubbers with built-in filters.
- **Best fit when:** The robot is fully submersible and lacks any ground or surface mobility.
**8479.89 – Industrial-grade robots**
- **Defining trait:** Intended for industrial or commercial use, often larger, more robust, and capable of handling heavy-duty cleaning tasks.
- **Typical examples:** Large pool cleaners used in public pools or water parks.
- **Best fit when:** The robot is built for frequent, high-volume use in large or commercial pools.
**8509.80 – Household robots under 20 kg**
- **Defining trait:** Specifically for home use and limited to devices weighing less than 20 kg.
- **Typical examples:** Lightweight, cordless pool bots for residential pools.
- **Best fit when:** The product is designed for average homeowners and meets the weight threshold.
## Key differences
| Feature | 8421.21 | 8479.89 | 8509.80 |
|-----------------------|---------------------|----------------------|--------------------|
| Operating environment | Only underwater | Industrial/commercial| Household only |
| Size/weight | Not specified | Typically heavy | <20 kg |
| Primary use case | Residential/submersible | Public or large pools | Home use |
## How to choose
- Is the robot designed only for underwater use and cannot operate above ground? → 8421.21
- Is it built for commercial or industrial pools (e.g., public facilities)? → 8479.89
- Is it intended for home use and weighs less than 20 kg? → 8509.80
## Overlaps & pitfalls
- A household robot under 20 kg that is fully submersible could fit both 8421.21 and 8509.80.
- Industrial robots may also be underwater but are not intended for home use.
- **Priority note:** If the product is for home use and under 20 kg, prefer 8509.80. Otherwise, prioritize function (industrial vs. residential) and environment (underwater-only vs. general)