The chest freezer cold plunge conversion, part by part

Read this first

What the conversion actually is

Strip the forum threads away and the build is four jobs, each needing a different part.

1. The box. A chest freezer supplies the insulated shell and the refrigeration. This is the part no maker will rate for water, and the part this site will not score. 2. The liner. A waterproof insert that keeps chlorinated water off the freezer’s own interior and stops the conversion from being a slow leak into an electrical appliance. 3. The setpoint. A plug-in temperature controller with its probe in the water, switching the freezer on and off, because a freezer left on its own dial does not make a plunge. 4. Circulation and treatment. Water that sits still in a warm garage goes off, so the build needs a pump moving water through a filter and a sanitizer dosing it.

The liner listings are candid about the shape of this. Both of them tell you to add the BoxPlunge filter and control box, both marked not included - and neither is sold on Amazon at all, which is why the controller and filtration picks here come from the controller roundup and the filter roundup instead. The maker sells a complete DIY kit on its own site at several times what the bare liner costs, and a finished plug-in unit at an order of magnitude more.

Why the box cannot be left on its own dial

This is the part of the build people underestimate, and the freezer listings make it obvious once you read the thermostat range rather than the capacity. One of the best-disclosed 7 cubic foot boxes on Amazon, read on 6 November 2026, publishes an adjustable range of roughly -7.6 F to 10 F. The second figure is the important one: at its warmest setting that freezer is 22 degrees below freezing. Left alone it does not produce a cold plunge, it produces a block of ice with nobody in it. Nothing is wrong with the appliance - it is a freezer being a freezer.

So the setpoint has to come from outside the box. A plug-in controller reads the water with a probe, cuts power to the freezer when the water hits your number and restores it when the water drifts up. Two published figures decide which controller: whether the probe is submersible, because a bead on a wire taped to a cabinet wall is not reading your water, and the maximum load it can switch. Match the second to the circuit rather than to the appliance: no chest freezer listing we read publishes a rated wattage at all, and a controller rated for 1,200 W or 1,800 W clears any 110 V household freezer because the branch circuit upstream is the real limit. The full controller comparison is here.

One exception is worth knowing about if you are still choosing a box. A handful of chest freezers are sold as dual-mode, with a published fridge range as well as a freezer range - one 14.5 cubic foot listing read the same day publishes 32 F to 46.4 F in fridge mode and -14.8 F to 10.4 F in freezer mode. A box like that will hold plunge temperature on its own dial with no controller in front of it, which removes a part and a probe from the build. It will not make ice in that mode, because the mode that reaches below freezing is the other one.

What size, and will you fit in it

Chest freezers are sold by storage volume in cubic feet, which is not a figure anybody shopping for a plunge thinks in. The conversion is exact arithmetic rather than an estimate: a cubic foot is 1,728 cubic inches, a US gallon is 231 cubic inches, so a cubic foot is 7.48 gallons.

Two warnings about that table. The gallon column is the rated storage volume converted, not the water you will put in: a liner takes up some of it, you need freeboard so the plunge does not overflow when you get in, and your own body displaces the rest. And no chest freezer listing we read publishes an interior dimension of any kind. The 7 cubic foot box above publishes a cabinet 20.23 inches deep, which puts the inside somewhere under 20 inches wide - narrow for an adult to sit down in, and the sort of thing you discover after delivery. The liner’s published compatibility band is the only fit guide in the whole build, and it tells you the liner fits the box, not that the box fits you. Measure your own shoulders against a 20 inch gap before ordering anything, and see how plunge sizing actually works.

What it costs to run, from the only figures measured in plunge service

Every running cost on this site is computed from a published figure at the current US average residential rate of 18.34 cents per kWh, and the chest freezer category almost never gives you one. Of the three boxes we read, one publishes about 0.92 kWh a day, one publishes a dollar figure a year with no electricity rate behind it, and one publishes nothing at all. Worse, the figures that do exist are measured in food service - an empty, sealed box at zero Fahrenheit - not with a hundred gallons of water being pulled down from room temperature, held at a setpoint, opened daily and warmed by a body.

The liner’s manufacturer is the one party that publishes energy for the actual use, and the figures are specific: 338 kWh a year for a 14.3 cubic foot freezer and 175 kWh a year for the filtration. Recomputed at the rate this site uses rather than the rate its own page assumes:

That is about 25.8 cents a day to own a cold plunge that holds temperature around the clock, and it is a genuinely low number - the insulated, sealed, lid-closed box is doing exactly what a chest freezer is good at. Treat it as the best case rather than the bill. It is the maker’s figure for its own installation, not a measurement of yours, and a garage at 95 F in August is not the condition it was derived in.

Forty-eight hours, and you still buy ice for the first fill

The maker publishes the one expectation no forum post sets: water may take 48 hours or more to reach low temperatures, 72 hours for the largest box, and it recommends using ice on the first fill to get there. It also recommends unplugging the water pump during that initial cool-down, because a pump adds heat to the water it is circulating. After that first pull-down the picture inverts - the same page says that once cold, the box holds water at freezing temperatures without added ice, which is the thing an uninsulated tub and a 42 F chiller cannot do at all.

That is the honest case for this build. Not that it is cheap, and not that it is better, but that it reaches and holds a temperature band the purpose-built category mostly does not serve. Of the cooling devices tracked on this site, four publish a 42 F floor, one publishes 37 F and one publishes 32 F. If you want water in the low thirties with ice forming at the edges, there is one product on this site that publishes a floor low enough, and a freezer does it by design.

The gap between a kit and a liner, in the maker’s own words

This is the paragraph to read twice, and the evidence for it comes from the company that sells the liner rather than from us. On its finished units, that company publishes three separate electrical provisions: the electronics automatically disconnect whenever the lid is opened, with a click you can hear and a thermostat display that goes dark; all the electronics are GFCI protected; and the unit ships with a water-safe GFCI plug. Having fitted all three, the same page still tells owners to unplug before getting in, and calls its own lid cutoff a redundant measure.

A liner and a generic plug-in thermostat give you none of the three. You get a waterproof insert and a device that switches a mains outlet on and off next to a hundred gallons of water, with no lid interlock, no GFCI unless the outlet already has one, and no interlock between the pump and the lid. That is the real difference between buying a conversion kit and assembling one from parts, and it is not a difference in temperature or in cost. If you build this, put it on a GFCI-protected circuit, unplug everything before you get in, and treat the lid as an electrical switch rather than a lid.

One more published detail worth carrying across. The maker says the interior of its own units is enameled coated metal, designed to be skin-safe, waterproof and corrosion-proof. The liner listings on Amazon describe their product only as smooth and waterproof and name no material at all, so if the material is what you are buying for, that figure lives on the manufacturer’s site and not on the listing you are ordering from.

Why the freezer is still not scored here

Every product on this site gets scored on what its manufacturer publishes for the use we are recommending it for. A chest freezer fails that test on its face: no maker rates one for holding standing water that a person gets into, none publishes a volume rating for water, a draw under that load, a seal specification for it or a warranty that survives it. So the freezer is not in the picks on this page, it carries no score, and there is no buy link for one anywhere on this site. That position has not changed and this page does not soften it - the DIY page states it in full.

What has changed is that one part of the build now has a manufacturer behind it. The liner is sold for this exact conversion, publishes a compatibility band, and its maker publishes energy, cooling time and safety provisions for a freezer used as a plunge. That is checkable, so it is scored. The box it goes inside is not, and the scores on this page are scores of parts rather than a verdict on the build.

If the temperature floor is not the point, buy the other thing

Most people who search for this build are looking for a cheaper plunge, and on live prices that is not what it is. A chest freezer in the size the liners are made for sits in the same price bracket as a complete tub-and-chiller bundle - and the bundle arrives in one order with a chiller, a pump, a filter and a tub, from a maker that rates the whole thing for water. The liner, the controller, the filter housing, the cartridge and a circulation pump are all additional to the box.

Note that last item, because nothing in this build moves water on its own. A filter housing is a canister, not a pump, and no standalone circulation pump is tracked on this site, so budget for one on top of everything in the picks above. If what you actually want is 40 F water with the least money and the fewest parts, start with the cheapest setups that publish figures or a tub and chiller pairing. Come back to the freezer when the thing you want is ice.