How to size a cold plunge chiller

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.

Every chiller listing in this category says 'quiet' and exactly one publishes a figure. Thirty to forty decibels is genuinely quiet - roughly a library, well under a household refrigerator - and whether or not the figure is generous, publishing a number you can be held to is a different act from printing an adjective.

This matters more than it sounds in a small space. A chiller sitting next to a balcony door in a one-bedroom apartment runs for hours, often overnight, and a unit that turns out to be as loud as a window air conditioner is one you stop using.

The published range of 41 to 55 F is a range rather than a floor, which is a slightly weaker claim than the single-figure floors elsewhere. At 1,200 W and a 105-gallon rating it is otherwise a conventional half-horse unit: twenty-two cents an hour at full draw, same as the PlungeFit.

Two hundred and thirty gallons at 37 F is the largest published capability in this roundup, and it is the only unit that plausibly pairs with the 216-gallon tubs elsewhere on this site. Sizing a chiller under its tub is the most common expensive mistake in this category: an undersized unit runs continuously, never reaches setpoint, and costs more in electricity than the right one would.

The wattage is not published, which on a 1 HP unit is a real gap. The TURBRO in this roundup is also 1 HP and publishes 1,030 W, so the order of magnitude is not a mystery - but we are not going to attribute another manufacturer's figure to this one, so the cost-to-run component scores zero and the score reflects it.

At 83 pounds this is by far the heaviest chiller here, which is why the caster wheels are a specification rather than a nicety. It is also why the external filter matters: a 20-micron cartridge you can change without moving the unit is the difference between maintaining it and not.

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.