Start with water volume and the hottest realistic ambient condition, then define target temperature and acceptable pull-down time. Add insulation, sun, lid, user heat, pump flow, pipe restriction, and ventilation. Compare BTU/h and operating envelopes; horsepower labels alone do not establish performance in your setup.
Quick comparison
| Input | Why it matters | Conservative move |
|---|---|---|
| Volume | More water stores more heat | Use actual fill, not shell volume |
| Ambient | Raises heat load | Design for hottest week |
| Target | Larger delta needs more capacity | Avoid marketing-only floor |
| Insulation | Cuts ongoing load | Insulate tub, lid, hoses |
| Airflow | Rejects condenser heat | Keep clearance and clean coils |
What should a sizing quote contain?
Ask the seller to state assumptions: gallons, starting and target temperature, ambient air, sun, insulation, pump, and expected hours. A promise without these inputs is not a sizing calculation.
- Compare BTU/h at relevant conditions.
- Confirm the unit is outdoor-rated if exposed.
- Plan freeze protection.
- Include filtration pressure drop.
Sources and evidence labels
Official sources support product facts; research sources support broader safety or physiology context; community-pattern links identify recurring owner questions and are not treated as product proof.
- officialPenguin chiller sizing guide
- officialPenguin 1/2 HP specifications