What Size Chiller for a Cold Plunge?
The honest answer is a BTU/hr number, not a horsepower guess. Pick your tub volume below for the exact figure, or open the calculator to factor in insulation, a cover and climate.
By volume
50-gallon plunge
~5,831 BTU/hr · 0.58 HP75-gallon plunge
~8,747 BTU/hr · 0.87 HP85-gallon plunge
~9,913 BTU/hr · 0.99 HP100-gallon plunge
~11,662 BTU/hr · 1.17 HP120-gallon plunge
~13,994 BTU/hr · 1.4 HP150-gallon plunge
~17,493 BTU/hr · 1.75 HP
~5,831 BTU/hr · 0.58 HP75-gallon plunge
~8,747 BTU/hr · 0.87 HP85-gallon plunge
~9,913 BTU/hr · 0.99 HP100-gallon plunge
~11,662 BTU/hr · 1.17 HP120-gallon plunge
~13,994 BTU/hr · 1.4 HP150-gallon plunge
~17,493 BTU/hr · 1.75 HP
Figures assume an insulated, covered tub and a 28°F pull-down in 2 hours. Open the full chiller calculator › to change those.
By horsepower (rough guide)
Chillers are sold by HP, but HP only loosely maps to cooling power (≈ 10,000 BTU/hr per HP). Use this to sanity-check, then size on BTU/hr for your actual tub:
| Chiller | ≈ BTU/hr | Typical tub (insulated) |
|---|---|---|
| 1/4 HP | ~2,500 | up to ~50 gal |
| 1/2 HP | ~5,000 | ~50–85 gal |
| 3/4 HP | ~7,500 | ~85–110 gal |
| 1 HP | ~10,000 | ~100–150 gal |
| 1.5 HP | ~15,000 | large or outdoor tubs |
An uninsulated or outdoor tub needs the next size up, sometimes two — the calculator applies those corrections for you.