Best Metal Tubs for Ice Baths: Galvanized, Stainless or Poly

Metal tubs, measured.

Stock tanks ship nested two or three inside each other, so the "2 x 2 x 6" you bring home can be any of two or three sizes. Here's the spread, from the makers' own tables.

Size it to your body, not the gallons.

A 2-foot tank is 23.5 to 24 inches tall. Sitting upright, the average man's shoulders are about 23.7 inches above the floor and the average woman's about 22.2, according to the US Army's ANSUR II body survey of 6,068 adults (worked out from standing shoulder height, stature and sitting height). So in any 2-foot stock tank you recline, and reclining takes length.

• Length. Lying back far enough to get your shoulders under 20 inches of water with legs straight takes about 59 inches for an average man, 54 for an average woman and about 65 for the biggest 5 percent of men. A 4-foot tank means knees up for nearly everyone. A 6-foot tank fits most adults stretched out, even the smallest tank in the nest.
• Width. Seated hip width averages 14.9 inches for men and 15.7 for women, with the widest 5 percent past 17 and 18. Steel tank walls run straight down, so even a 20.5-inch "C" tank clears nearly every pair of hips. Shoulders are the tighter fit: men's average 20.1 inches across, and about a third of the men in the survey are wider than 20.5. If you're broad, get the A or B tank.
• Nest size. Behlen's 2 x 2 x 6 runs from 70.25 x 26.5 inches down to 65.75 x 20.5. Tarter's runs from 131 to 167 gallons. Ask the store which one is on the floor, or bring a tape measure.
• Real fill. An oval 68 x 24 inches holds about 6.5 gallons per inch of depth. At 20 inches that's 131 gallons, and with a 180-pound adult inside (roughly 20 gallons displaced) about 110 gallons of water. That's 57 pounds of ice to go from 60 to 50°F, or 114 pounds from 70 to 50°F, before sun and air add their share. Our ice calculator does the rest.
• Weight. 170 gallons of water is about 1,418 pounds. In use with an adult inside, a 2 x 2 x 6 puts roughly 110 pounds per square foot on the ground. Prescriptive deck guides are built around 40 pounds per square foot and leave hot tubs out entirely, so set it on the ground, gravel or a slab.

Galvanized, stainless or poly.

Galvanized steel

Steel sheet with a zinc coating. Tarter's tanks use 20-gauge galvanized bottoms, 21-gauge sides and a G90 coating, which is 0.90 ounces of zinc per square foot of sheet across both sides: about 21 microns (0.0008 inch) on each surface. That zinc is the whole rust protection, and it wears away sacrificially. Galvanized tanks are cheap, stable in sun and wind, and come in the long sizes plunging needs. They're sold for livestock, planters and drink coolers, with one-year warranties from both Behlen and Tarter.

Stainless steel

No coating to wear through. Stainless shows up as complete plunges rather than bare tanks: the Finnmark SoulCold uses a 304 stainless interior. For tubs that sit in chlorinated water all the time, galvanizing-industry guidance names Type 316 stainless as the material that holds up, so with 304, follow the maker's water-care procedure rather than improvising with pool chemicals.

Poly

A structural foam tank like the Rubbermaid Brute 150 can't corrode, has no bottom seam, and its spec covers water from 32 to 120°F. Its sloped walls make a backrest. If you like the stock tank idea but not the chemistry lesson, it's the better buy, and our budget cold plunge guide covers it in detail.

Aluminum and "tin"

Old "tin" washtubs are galvanized steel, and common ones, like Behrens' 16-gallon round tub, are a foot bath, not a plunge. Marine-grade aluminum appears in the galvanizing industry's list of materials suited to chlorinated water, but aluminum tubs big enough to sit in are hard to find.

Zinc and your water chemistry.

Every water care choice you make in a galvanized tank is also a choice about the coating. Here's what the coating cares about.

• pH. The American Galvanizers Association says galvanized steel performs best between pH 5.5 and 12 and that pH 3 to 5.5 is corrosive. Most tap water sits inside that window. Acidic "pH down" products push the other way, so test before you dose.
• Soft water. The same group says soft water (under 17 ppm hardness) is much more corrosive to galvanized steel than hard water, because the protective mineral scale never forms. If your house has a softener, fill from a spigot that bypasses it, if you have one.
• Chlorine. Galvanizing-industry guidance says hot-dip galvanized steel isn't acceptable for continuous immersion in chlorinated water and puts zinc loss in that service at 10 to 50 or more microns a year. Against a 21-micron G90 skin, that's somewhere between about five months and two years before bare steel. A tablet floater parked against the wall concentrates it in one spot. If you want chlorine, line or coat the tank first (paint or epoxy over zinc is the "duplex" system the industry recommends for harsh conditions) or buy poly.
• Hydrogen peroxide. Peroxide is an oxidizer, and its safety data sheets list zinc among the metals to keep it away from; a 25% peroxide sheet names 304L and 316L stainless and polyethylene as suitable containers and rules out zinc. Those sheets are written for concentrated product, not the 50 to 100 ppm a plunge uses, but the zinc still gives the peroxide something to react with besides what's in the water. Dilute each dose in a bucket of tank water, pour it into the middle rather than down the wall, and dose by peroxide test strip, not by calendar. Our peroxide guide has the dosing chart.
• Brass and copper. The Steel Tube Institute puts copper and brass far from galvanized steel on the galvanic series and warns that severe corrosion can follow when they're joined in an electrolyte, which tap water is. The zinc is the metal that loses. Use plastic or galvanized fittings on the drain, and isolate any metal chiller connection.

Seams, plugs and the last inch.

On Tarter's tanks the bottom is a rolled joint, not a weld: Tarter describes a four-ply double-lock seam sealed with Pliogrip adhesive, rolled three times around the bottom before the sealer goes on, and says it water-tests three or four sets of tanks a day. That crimp holds the water in, and it's a crevice where water sits against the metal, so it's where leaks and corrosion tend to show up first.

• Inspect before the first fill and every water change: look along the bottom seam inside and out for white crust, rust or weeping.
• Keep the base dry. Set the tank on a level pad that drains, like gravel or pavers. A puddle under the tank keeps the outside of the seam wet too.
• Drain it; don't tip it. A full 2 x 2 x 6 weighs about 1,400 pounds. Dragging or tipping a full tank strains the same seam.
• Know your plug. Behlen's 2-foot tanks have a drain plug that takes a 3/8-inch ratchet; Behlen lists the plug for its 2-foot tanks only. Tractor Supply lists a 0.75-inch threaded plug on the CountyLine WT226CL. Farm King lists a 1-inch plug on the Tarter Oval Mega 300. Tarter sets its plugs in the side about an inch above the bottom, so keep a sponge or wet-vac for the last inch.

Outdoor freezing and indoor sweating.

Water expands about 9 percent as it freezes (USGS), and a full tank that freezes solid has nowhere to put that. If you're not plunging through a hard freeze, drain the tank and leave the plug out so rain doesn't refill it. If you are, keep it covered and keep a hole open; our winter freezing guide covers insulation and de-icers. A stock tank de-icer is a heater in the water: plug it into a GFCI-protected outlet, and unplug it and lift it out before anyone gets in.

Indoors, a thin steel wall full of 45°F water sits below the dew point of many rooms, so it sweats. Put a metal tub on a floor that can take water. A steel wall adds almost no insulation either; a cover and insulation keep the cold, not the metal.

The picks.

For the other complete plunges, stainless or not: browse cold plunges at Sauna Marketplace.

FAQ

What is the best metal tub for an ice bath?

For one person on a budget, a 2 x 2 x 6 ft galvanized oval stock tank: long enough to recline with your shoulders under, about 110 gallons of water in use. For metal that needs no coating care, a stainless plunge such as the Finnmark SoulCold.

What size metal tub do I need for an ice bath?

In a 2-foot-tall tank you recline, which takes about 59 inches of length for an average man and 54 for an average woman. That makes a 6-foot tank the right choice for most adults and a 3 x 2 x 8 the large option for two people or very tall plungers.

Can I use chlorine in a galvanized stock tank?

Not if you want the coating to last. Industry figures put zinc loss in chlorinated water at 10 to 50 or more microns a year against about 21 microns of zinc per side on G90 steel. Coat or line the tank first, or use poly.

Can I put hydrogen peroxide in a galvanized tub?

Yes, with care. Dilute each dose in a bucket first, pour it mid-tank, and dose by test strip, since peroxide also reacts with zinc. Never mix it with chlorine or anything else.

Will a galvanized stock tank rust?

Eventually, starting where the zinc goes first: the bottom seam, scratches and spots where chemicals sat. Keep pH between 5.5 and 12, avoid softened water, skip chlorine and brass fittings, and keep the base dry.

Is a tin tub the same as a galvanized tub?

Usually, yes: "tin" washtubs are galvanized steel. Common ones, like Behrens' 16-gallon tub, are far too small to sit in; a plunge needs a 2-foot-tall stock tank.

Can I use an aluminum tub for an ice bath?

Marine-grade aluminum handles chlorinated water better than zinc, according to galvanizing-industry guidance, but aluminum tubs large enough for an adult are hard to find. Stainless and poly are the practical alternatives to galvanized.

Does a metal tub keep the water colder?

No. A thin steel wall adds almost no insulation, and it sweats indoors. Covers, insulation and shade keep water cold; see our budget cold plunge guide for what ice and chillers take to run.

Can I leave a galvanized tank outside in winter?

Drain it if you're not using it, and leave the plug out. If you plunge through winter, cover it and keep a hole open, and unplug and remove any de-icer before getting in.