DIY Cold Plunge: Bathtub, Chest Freezer, Stock Tank or Portable Tub?

Your bathtub: the cheapest way to start

The bathtub you already have is the simplest way to try an ice bath: there is nothing to buy except ice. Its limits show up fast. It holds a lot of water, and every gallon you want to chill needs its share of ice, so it takes whole bags just to drop the temperature a few degrees. Bathrooms tend to be warm, and a bathtub has no lid and no insulated wall, so the water warms up while you get ready. Finally, you lie back in a bathtub more than you sit, and it is rare to be able to sit up straight with the water at shoulder height.

To use less ice, fill only as much as you need, start with the coldest tap water you can get and add the ice at the last moment. Measure the temperature instead of guessing. A bathtub is still a good way to find out whether the routine suits you before buying dedicated gear, and it has one advantage the other options do not always have: the drain is already there.

Converted chest freezer: why we advise against it

The idea gets shared a lot: fill a chest freezer with water and run it to keep the water cold without buying more ice. It is the only DIY option that chills on its own, which explains its popularity. But it puts water, a person sitting in that water and an appliance plugged into a wall outlet all in the same space. A freezer is not designed for anyone to get into the water it holds, and a mistake in the wiring, a seal or the installation becomes an electrical risk for the person in the water. The unit is also heavy, and hard to move once it is filled.

For that reason, we advise against building this setup yourself. If you are set on it, an electrician's opinion is essential before any water goes in, for the appliance as well as the outlet and the circuit that powers it. The same rule applies to any electrical appliance placed near water, chillers included: the installation has to be suitable, and a professional is the one to judge that. Also think about the weight of the full setup, which needs a level floor that can carry the load.

Stock tank or rain barrel: plenty of volume, everything else to add

A large rigid plastic container, such as a livestock stock tank, or a rain barrel gives you a lot of volume with no frame to assemble. These containers are made for outdoor use and hold water without any trouble. Their limits lie elsewhere. They are heavy and bulky: once in place, they stay put and take up a corner of the backyard all year. Above all, they come without a fitted lid or any insulation. The water then follows the air temperature and the sun, and ice melts quickly behind a single exposed wall.

So you have to add everything yourself: a rigid lid that really closes, insulation around the wall, a base under the bottom, and a way to drain it without spilling. A rain barrel, tall and narrow, also means climbing in and out over the top, with a stable step. These options suit people who enjoy DIY projects and have a backyard, much less someone with a balcony.

Portable insulated tub: foldable and covered, but no chiller

A portable insulated tub is designed for this use. The one in the kit is round, black, foldable and held up by 6 support tubes; only the top ring inflates, forming the rim and serving as a neck rest. It measures 33.5 in (85 cm) across and 29.5 in (75 cm) tall on the outside (31.1 x 26.8 in, or 79 x 68 cm, on the inside), holds 87 gallons and weighs 8.4 lb empty. Its wall has 3 layers, with an aluminum-lined foam in the middle. An insulated lid closes it, a water-filled cushion lets you sit up straight, and a drain hose with a valve, plus a plug in the bottom, let you empty it.

Its limit is clear: it has no chiller and is not designed to take one. So the ice does the cooling, just as in a bathtub. The lid and the insulated wall are there to slow down warming, with no duration promised: in summer, the water still warms up, which is why shade and a closed lid matter. Once drained and dried, the tub folds into a zippered carry bag.

How much ice do you need, whatever the option?

Without a machine, none of these setups lets you skip the ice, and the amount can be calculated. Melting 1 lb of ice absorbs about 144 BTU, while cooling 1 lb of water by 1 °F takes about 1 BTU. That gives the formula: ice (lb) = W x (starting temp - target temp) / (144 + target temp - 32), where W is the weight of the water in pounds (about 8.3 lb per gallon) and temperatures are in °F. For 66 gallons, which is the tub filled with room left for the person, that works out to:

• From 68 °F to 59 °F: about 29 lb of ice
• From 68 °F to 54 °F: about 48 lb
• From 68 °F to 50 °F: about 61 lb
• From 59 °F to 50 °F: about 31 lb

These figures are a physical minimum, with no losses at all. In practice you need more, because the air, the ground and the sun keep warming the water: keep the lid closed and add the ice just before the plunge. Starting with cooler water changes everything: to reach 50 °F, it takes 61 lb from 68 °F but 31 lb from 59 °F. The Ice Bath Tub shop sells a single portable insulated tub with a lid, as a complete kit (what's in the box: the tub and its 6 tubes, lid, dust cover, pump, cushion, drain, patches and carry bag), shipped free from stock in your region.

Safety: the same rules for any home setup

See a doctor before your first cold plunge if you have heart disease, high blood pressure, a heart rhythm disorder, a circulatory disorder (including Raynaud's syndrome), diabetes or epilepsy, if you are pregnant or if you are on medical treatment. Never take an ice bath alone: someone present and attentive stays close by. Get in slowly, breathe calmly, start with 1 to 2 minutes and keep your head above water. Cold shock can happen in water at 59 °F or below: it takes your breath away and speeds up your heart, one more reason to get in slowly. Get out right away if you feel dizzy or have chest pain, numbness or uncontrollable shivering. No alcohol, no drugs and no medication that makes you drowsy.

Ice baths are off-limits to children, and any water stored at home is a drowning risk for them. Close the lid when not in use, empty the container when no one is watching it and never leave a child nearby without an adult; a bathtub or tank without a lid calls for the same care. Keep any electrical appliance away from the water unless an electrician has approved the installation. Finally, set the tub on a level floor that can carry the load: 87 gallons of water weigh about 730 lb, plus the person.