What the research used
The largest pooled analysis of cold water immersion for muscle soreness found the best results with water at about 11–15 °C for 11–15 minutes (Machado et al., Sports Medicine 2016). That is warmer and longer than many routines you see online. The studies do not show that colder water works better for recovery; colder water mainly makes the same minutes harder. Cold plunge benefits sums up what the research does and does not show, including the findings on strength training.
How cold the equipment goes
The plunge tubs with built-in chillers we looked at list minimum water temperatures between about 0 and 4 °C (32.5 to 39 °F), most of them around 3 °C (37 °F). A chiller's display is a setting, not a measurement of the whole tub: check it with a separate thermometer.
Choosing a temperature
- Starting out: begin around 15 °C (59 °F) with short dips, and go colder over weeks only if you want to.
- After training: the recovery studies used 11–15 °C; if building muscle is your goal, keep plunges away from the hours right after strength training.
- Below 10 °C (50 °F): the water feels far more intense, so keep the time short.
- Time and temperature go together: the colder the water, the shorter the plunge. Get out if you shiver hard, feel numb or dizzy.
What each degree colder costs
| Water | Per month, indoors at 72 °F | Per month, outdoors in July | Cool-down of a fresh fill |
|---|---|---|---|
| 59 °F | 60 kWh · $11.03 | 63 kWh · $11.61 | 0.3 h |
| 55 °F | 62 kWh · $11.29 | 65 kWh · $11.93 | 1 h |
| 50 °F | 63 kWh · $11.62 | 67 kWh · $12.32 | 1.9 h |
| 45 °F | 65 kWh · $11.94 | 69 kWh · $12.72 | 2.9 h |
| 41 °F | 67 kWh · $12.21 | 71 kWh · $13.03 | 3.8 h |
| 37 °F | 68 kWh · $12.47 | 73 kWh · $13.35 | 4.8 h |
Model estimate: insulated tub and lid, a 4,500 BTU/h chiller (about 1,320 W of cooling) with a COP of 2 and a 50 W pump, two 3-minute plunges a day; electricity at $0.18/kWh (United States average). Outdoors uses the July average in Chicago, in the shade. The cool-down starts from 61 °F tap water.
With an insulated tub and a good lid indoors, holding 3 °C instead of 15 °C adds surprisingly little: in our model about 13% more electricity, because little heat gets through good insulation and the circulation pump uses about as much as the cooling. The bigger difference is the cool-down of a fresh fill, minutes at 15 °C and hours at 3 °C, and, outdoors in summer, the heat the chiller has to fight. Stock tanks and uninsulated barrels behave very differently: see DIY cold plunge. The running cost calculator works it out for your tub and prices.
Measuring the water
- Measure in the middle of the tub, at the depth where you sit, not at the chiller's inlet.
- Stir or run the circulation before you measure: with the pump off, the coldest water sinks and the surface reads warmer.
- Check the thermometer now and then in iced water, which sits at 0 °C (32 °F).
Safety
The first minute in cold water brings a gasp and a racing heart (cold shock): get in slowly, keep your head out and breathe calmly. Never plunge alone or after alcohol. If you have a heart condition or high blood pressure, or are pregnant, ask your doctor first. More in the safety guide.