Cold plunge running cost and chiller sizing: what it really costs to keep water at 45°F
A chiller is the part of a cold plunge that costs money every month. Here's how much electricity a plunge actually uses, what drives the number, and how to pick a chiller size that isn't too weak or too expensive.
Typical monthly electricity
| Setup | Water | Per month at 17¢/kWh |
|---|---|---|
| Insulated tub with lid, indoors or garage, 1/4 HP chiller | 70-100 gal | $8-$15 |
| Insulated tub with lid, outdoors in a mild climate, 1/3 HP | 80-120 gal | $12-$25 |
| Insulated tub outdoors in summer heat (90°F+ days), 1/2 HP | 100-120 gal | $25-$45 |
| Uninsulated stock tank, chiller, no lid, outdoors | 100-150 gal | $40-$80+ |
| Ice only, no chiller (stock tank or bathtub) | any | $0 electric; $5-$15 per bath in ice |
Chillers cycle on and off; the figures assume the compressor runs 20-50% of the time depending on insulation and ambient temperature. Multiply by your own electricity rate.
What drives the cost
- The lid. An open water surface loses heat (gains heat, in this case) fastest of all. A fitted insulated lid roughly halves running cost. Use it.
- Insulation. Purpose-built plunges (Plunge, Sun Home, Ice Barrel's insulated models, Morozko) have foam-insulated walls. A galvanized stock tank has none; the chiller runs constantly on a warm day.
- Ambient temperature. Pulling water to 45°F in a 65°F garage is easy. Doing it on a 95°F patio in July is where chillers struggle and bills climb.
- Target temperature. Each degree lower costs more. 50°F is plenty for the research-backed effects; 37°F is an ego number for most people.
- Water volume. More gallons take longer to chill initially but don't cost much more to maintain once cold, as long as the tub is insulated.
Chiller sizing
| Chiller | Suits | Where you see it |
|---|---|---|
| 1/4 HP | Up to ~80 gal, indoors or shaded; mild climates | Entry all-in-ones, add-on chillers for barrels |
| 1/3 HP | 80-120 gal; most residential plunges outdoors in temperate climates | The common mid-range size |
| 1/2 HP | 100-150 gal; hot climates; wants fast recovery between users | Premium plunges, commercial-leaning |
| 1 HP | 150+ gal or heavy daily use by several people | Commercial |
Two more specs matter as much as horsepower. Lowest set temperature: some chillers bottom out at 42-45°F; others reach 37°F. And built-in filtration and sanitation (pump, cartridge filter, ozone or UV), which decides how often you change water. See water care.
Running it in winter
In cold climates the chiller barely runs, but many plunges then need a heater to keep water from freezing, and all-in-one units with heat/cool are worth the premium there. Check the manual's minimum ambient temperature; most chillers stop working below about 40°F ambient, and ice in the lines ends the warranty.
Cost of ownership, all in
A $4,000 plunge used daily for three years, with $15/month electricity, two filter cartridges a year and water changes, costs roughly $4,700, or about $4.30 per plunge. A stock tank and ice costs less up front and more per session, and most people stop using it within a season because of the hassle; that calculus is in plunge vs ice bath vs cold shower. Picks are in best cold plunge tubs.