What a cold plunge chiller costs to run

Two hundred and eighty watts is the number that decides this category. At the current US residential average it costs about five cents an hour at full draw, and even running continuously for a month - which no chiller does - the absolute ceiling is around thirty-eight dollars. The 1,200 W units in this roundup are four times that.

The listing's own comparison is a good one: about the same as a home freezer. That is a useful mental model, because a chiller works the same way and cycles the same way. It draws its rated power while the compressor is running and almost nothing while it is not, and how often it runs depends on your lid discipline, your room temperature and how well your tub is insulated.

The published floor is 41 F, which is warmer than the 37 to 39 F claimed by the bigger units. For most people that is irrelevant - the commonly recommended starting band is 50 to 59 F and experienced plungers usually settle around 45 to 50 F - but if you specifically want to get below 40, this will not do it.

This is an aquarium and hydroponics chiller, and that is the case for it rather than against. Aquarium chillers have been made to the same job for decades, they are expected to run unattended for years, and the titanium evaporator exists because someone else's fish were going to be swimming in the water. That is a longer track record than the cold-plunge-specific category has existed for.

At 190 W it is the second-cheapest to run here, about three and a half cents an hour at full draw. The rated volume range of 40 to 92 gallons is the constraint - this is not enough compressor for a 216-gallon tub, and it will run continuously trying.

The one thing it does not publish is a floor temperature. Aquarium chillers are specified by cooling capacity and volume rather than by a target temperature, which is a different but perfectly reasonable convention, and it means you are sizing by gallons instead of by degrees. Match it to a tub under 92 gallons and it is the right tool.

The submersible pump is what makes this the bathtub answer. A chiller normally needs a tub with inlet and outlet ports; a bathtub has neither. Dropping a pump into the water and running two hoses over the rim is inelegant and it works, and it is the cheapest route to a cold plunge for anyone who cannot give up floor space for a tub at all.

Six hundred watts is eleven cents an hour at full draw, comfortably mid-range here. The 79-gallon rating is a good match for a standard bathtub, which holds somewhere between 40 and 80 gallons at plunge depth.

The reusable metal mesh filter rather than disposable cartridges is a genuine running-cost detail that gets ignored because it is not electricity. Cartridge filters are a recurring purchase; a rinsable metal screen is not, and over a year that difference is larger than the difference in power draw between two chillers.

This is what a complete chiller spec sheet looks like: 1,030 W rated power, 9,553 BTU/h maximum cooling capacity, AC 110 to 120 V at 60 Hz, a 36 to 86 F range, and a stated cooling time with the starting temperature named. Every one of those is checkable, and together they let you predict what the unit will do in your room rather than hope.

The BTU figure is the one nobody else publishes and the one that actually lets you size a chiller properly. Horsepower is a compressor rating, not a cooling rating, and the relationship between the two varies by design. BTU per hour is the heat actually removed, which is the number that matters when you are deciding whether it can hold 132 gallons at 40 F in a warm garage.

At 1,030 W it is nineteen cents an hour at full draw - lower than both 1,200 W half-horse units here despite being a full horsepower, which is either better efficiency or a difference in how the figures were derived. The three-stage filtration is named by micron rating rather than described, and the ozone generator is a real sanitation method rather than a marketing word.