Every cold plunge has to answer the same question: how do you get the water cold and keep it there? There are two answers, ice or a chiller, and they lead to very different buying decisions.
This article does the math on both. For the rest of the cold plunge decisions, start with the cold plunge buying guide.
Short answer: ice is cheap to start but heavy to keep up, roughly 50 lbs to drop a 95-gallon tub by 10°F. A chiller costs more upfront and runs on electricity, but it holds the temperature without any hauling.
The ice math
Melting ice absorbs about 334 joules per gram, and warming water takes about 4.18 joules per gram per degree Celsius (standard physics values).
Worked example: cooling about 95 gallons (360 kg) of water from 60°F to 50°F, a drop of about 5.6°C, takes roughly 8,400 kJ. Each kilogram of ice absorbs about 334 kJ melting plus about 42 kJ warming to 50°F. That’s about 22 kg, or roughly 50 lbs of ice, before counting heat leaking in from the air, the tub, or your body.
| Tub size | Drop of 10°F (about 5.6°C) | Approximate ice needed |
|---|---|---|
| 95 gallons | 60°F to 50°F | about 50 lbs |
| 105 gallons | 60°F to 50°F | about 55 lbs |
These are lower bounds. Real use takes more, especially outdoors in summer.
The chiller math
A chiller trades ice for electricity. Renu lists the Cold Stoic 2.0’s chiller at 0.25 HP and 450W. If it ran nonstop for 24 hours, that’s 10.8kWh, about $1.98 at the 2026 U.S. average of 18.34¢/kWh (EIA). It cycles off once the water reaches temperature, so daily use is usually less.
Chillers also differ in speed:
| Tub | Chiller (per listing) | Cooling |
|---|---|---|
| The Plunge Original | Not stated in HP | To 37°F, 8–10°F per hour |
| Renu Cold Stoic 2.0 | 0.25 HP, 450W | To 39°F |
| Renu Siberian Pro | 0.8 HP | To 37°F |
| Nurecover Plunge + Chiller | 0.3 HP | 70°F to 41°F; 12–24 hours from ambient |
Which one fits you
You get a low entry cost with ice, and nothing to plug in. You give up convenience: every session means buying or making ice.
You get the same temperature every day with a chiller, plus filtration in most models. You give up a much larger upfront cost and a circuit, usually a dedicated 120V/15A.
My rule of thumb: if you plunge more than twice a week, a chiller usually wins on time and hassle. If you plunge occasionally, start with ice and see whether the habit sticks. The ice bath buying guide covers that route.
For four chiller tubs side by side, see our cold plunge comparison.
Bottom line: ice is a running cost you carry; a chiller is a running cost you plug in. Frequency decides which is cheaper for you.
Sources
- Physics LibreTexts, “Phase Change and Latent Heat” (latent heat of fusion of water, 334 kJ/kg), accessed October 2, 2026: libretexts.org
- U.S. Energy Information Administration, Electric Power Monthly, Table 5.6.A (residential average 18.34¢/kWh, June 2026 data), via energyfactbook.com, accessed October 1, 2026
- Chiller specifications: The Plunge, Renu Therapy, and Nurecover listings, checked September–October 2026