Use published BTU/h as the primary cooling-capacity number and keep rating conditions attached to it.
1. What HP tells you
Horsepower is a machinery class, not a universal refrigeration-capacity conversion. Compressor, refrigerant, heat exchanger and rating method differ by product.
2. What BTU/h tells you
BTU/h maps directly to heat-removal rate. That makes it more useful for a water-cooling problem, but it still must be interpreted under its rating conditions.
3. Real examples
| Model | Nominal HP | Published BTU/h |
|---|---|---|
| Active Aqua AACH50HP | 1/2 HP | 4,020 |
| Penguin Standard | 1/2 HP | 5,000 |
| Penguin High Efficiency | 1/2 HP | 5,750 |
Those are meaningfully different outputs behind the same nominal HP label.
4. Rating conditions matter
Active Aqua publishes both BTU test conditions and separate performance-chart conditions. Its manual explicitly says refrigeration efficiency depends on ambient, installation, heat sources, pump and connecting parts. That is why a sourced BTU plus a rating note is better data than HP alone.
5. How to compare chillers
- BTU/h and test/rating note.
- Minimum/maximum flow.
- Operating water range.
- Indoor/outdoor rating.
- Electrical input.
- Connections and service support.
- Independent evidence from similar setups.
Primary technical references
6. Normalize the comparison before ranking products
BTU/h is a better starting point than HP, but even BTU/h should not be ranked blindly when the manufacturers used different test conditions. Keep the rating note attached to every number. A product with a larger published figure under warmer water or easier test conditions may not deliver the same advantage at cold-plunge temperatures.
| Metric | Useful for | Do not use it alone for |
|---|---|---|
| Nominal HP | Rough product class / naming | Cooling capacity |
| Published BTU/h | Heat-removal capacity at stated conditions | Exact low-temperature performance without rating context |
| Electrical watts | Circuit/load planning and energy arithmetic | Cooling output |
| Required flow | Pump/plumbing compatibility | Thermal sizing |
| Capacity curve/map | Understanding changing performance across conditions | Anything outside the map without uncertainty |
This is also why ChillSizer keeps a confidence grade. A sourced capacity number with a full performance map supports a tighter model than a single marketing number with no cold-water context.
Use comparable data
Nominal horsepower is not a standardized promise of delivered cooling at your water temperature. Compare published BTU/h, electrical input, rating conditions and low-temperature evidence. Two “1/2 HP” products can have meaningfully different published capacity and minimum-flow requirements.
Related system resources
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