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What Size Chiller for a 50-Gallon Cold Plunge?
Direct answer first, then the heat-load math and how insulation, cover and climate change it.
| Insulated & covered (indoor) | 5,831 BTU/hr · 0.58 HP |
|---|---|
| Uninsulated, outdoor summer | 10,933 BTU/hr · 1.09 HP |
| Assumptions | 28°F pull-down in 2 h |
| Est. running cost | ~$4.44/mo · ~$53/yr (~0.9 kWh/day @ $0.17/kWh) |
Corrections the calculator applies: no insulation ×1.5, no cover ×1.2, outdoor in hot summer ×1.25 (they stack). HP ≈ BTU/hr ÷ 10,000.
Size it for your setup
Chillers near 5,831 BTU/hr
0.5 HP · 5,750 BTU/hr · 37F min
0.5 HP · 5,115 BTU/hr
0.5 HP · 37-104F
FAQ
What size chiller for a 50 gallon cold plunge?
Plan on about 5,831 BTU/hr (roughly 0.58 HP) to pull a 50-gallon insulated, covered tub down 28°F in 2 hours. That figure sizes the harder job, the first pull-down from a warm fill; holding an already-cold tub takes a fraction of it. An uninsulated tub sitting outdoors in summer is the worst case and needs closer to 10,933 BTU/hr (about 1.09 HP), so insulation and a cover effectively let you buy a smaller chiller. If you are happy to wait longer for the initial chill, a lower-powered unit still gets there, just more slowly.
How much does a 50-gallon cold plunge cost to run?
Around $4.44 a month (about $53 a year, or roughly 0.9 kWh a day) at $0.17/kWh, assuming about 6 hours of compressor time a day to hold temperature. Real usage swings with your climate and how well the tub is sealed: a cover alone can cut the run time noticeably because most of the heat a plunge fights is warmth creeping back in from the air and sun, not the water itself. Running it in a cool garage instead of open sun makes a bigger difference than most people expect.
Do I need ozone or filtration on the chiller?
Neither changes the size you need, but both change how often you drain the tub. Filtration pulls out the skin cells and oils you shed each session, and ozone oxidises what is left without leaving a chemical smell or residue, so the pair keeps one fill clean for weeks instead of days. If you plunge alone and keep it covered you can skip them and just change the water more often; if the tub is shared or used daily they are worth it. The spec table flags which chillers include each.