Ice vs Chiller Calculator: When Does a Chiller Pay Off?

Bagged ice is the cheap way into cold plunging until it is not. Every plunge needs the water pulled back down to temperature, and melting ice is the only thing doing that work, so the bill rises with every session you add. A chiller costs more on day one and then only the electricity to hold the water cold. Enter your tub, how often you plunge, what you pay for ice and what the chiller would cost, and this calculator shows the ice cost per plunge, the monthly cost of each option and how many months until the chiller has paid for itself. The key insight: the ice you need rises in step with the gap between your starting water and your target, so cooling from 12°C to 5°C takes more than twice the ice of cooling from 8°C. That is why a chiller pays back fastest for people who plunge cold and often through the summer.

How the calculator works

The ice figure is plain physics, the same method as our ice bath ice calculator. Cooling water by 1°C takes 4.186 kJ per kilogram, and a litre of water weighs about a kilogram. Each kilogram of ice soaks up 334 kJ as it melts, and its meltwater then warms from 0°C up to your plunge temperature. Divide the heat that has to come out of the water by what each kilogram of ice can absorb and you have the ice for one plunge. The melt allowance then covers heat that leaks in from the air, the sun and your body while the ice is working.

You buy ice in whole bags, so the cost per plunge is rounded up to whole bags. A month is taken as 52 weeks divided by 12. The chiller side is the price you enter plus the monthly electricity figure; it leaves out the pump, filters and sanitiser, because an ice-filled tub that you keep rather than empty needs those too.

Reading the answer

• Payback in months is the chiller price divided by what you save each month by not buying ice. If the chiller's electricity costs more than your ice, it never pays back and the calculator says so.
• Break-even plunges a week is the point where the ice bill matches the chiller's electricity. Plunge less often than that and ice stays cheaper to run, whatever the chiller cost.
• Seasons matter. The water you start from is colder in winter, so you need far less ice then. Run the calculator twice, once with a summer starting temperature and once with a winter one, to see the range across the year.

If the numbers point to a chiller, the next question is how big. Our chiller size calculator works that out from your tub and your climate.