Free tool
Cold plunge chiller calculator
Work out the cooling energy your plunge needs, the chiller capacity to pull it down in time, and what it costs to hold 4–8 °C all day. Insulation and a cover change the answer more than tank size does.
New to cold water? Read our ice bath temperature guide for the ranges operators actually run.
Tank volume
Temperatures
Build & operation
Water volume
784L
0.78 m³ of water.
Cooling energy
10.7kWh
Heat to remove for the pull-down, at 85% system efficiency.
Chiller capacity
3.00kW
Calculated requirement 2.70 kW including holding load.
Pull-down time
~3.6hrs
With the recommended chiller, from the starting temperature.
Holding energy
0.1kWh/day
Electrical energy to hold target against ambient heat gain (COP 3).
Cost per day
€0.23
Holding load plus an amortised weekly pull-down.
Modelled estimates. Real figures move with guest load, water changes, pump run time and how long the cover stays off — the things SenseStack measures continuously in the tank.
How the numbers are worked out
Cooling energy
Water needs 1.163 Wh per litre per °C. Multiply by the temperature drop and divide by 85% to allow for real-world losses in the loop.
Holding load
The tank is treated as a cube with a U-value of 0.35 (insulated and covered) up to 1.3 W/m²K (bare and open), against the ambient temperature difference.
Chiller sizing
Capacity must cover the pull-down within your chosen window plus the continuous holding load, rounded up to the next standard chiller size.
Running cost
A chiller moves roughly three units of heat per unit of electricity (COP 3). Daily cost is the holding energy plus one pull-down spread across a week.
Sizing is a one-off. Staying in band is every day.
A correctly sized chiller still drifts out of the 4–8 °C band on a busy Saturday, after a water change, or when a cover is left off overnight. SenseStack measures the water continuously and shows one readiness state per asset, so staff know before a guest does — and you can see how many hours a month you actually spent in band.
Common questions
What size chiller does a cold plunge need?
Size the chiller for two jobs: pulling the water down from ambient within an acceptable window, and holding it against daily heat gain. As a rule, 1 kW of cooling removes about 860 litre-degrees per hour, so a 500 litre tank dropping 10 C needs roughly 5.8 kWh of cooling and about 1.5 kW of capacity to do it inside four hours.
How long does a cold plunge take to cool down?
Pull-down time equals the cooling energy required divided by chiller capacity, allowing for around 85% real-world efficiency. Most commercial plunges take three to eight hours from ambient. A lid and insulation cut both the pull-down load and the holding load significantly.
What temperature should a cold plunge be?
Most operators run between 4 C and 8 C. Below 4 C the water approaches its density limit and guest tolerance drops sharply; above 10 C the plunge stops delivering the cold shock guests expect. SenseStack treats 4 to 8 C as the standard ready band for plunge assets.
How much does it cost to run a cold plunge?
Running cost is driven by holding load rather than pull-down. An uninsulated 500 litre tank in a 18 C room can lose enough heat to require 4 to 8 kWh a day of cooling, while the same tank insulated and covered may need under 2 kWh. At Irish commercial rates of about EUR 0.35 per kWh that is the difference between roughly EUR 2.50 and EUR 0.60 a day.