Grizzly cold plunge: the cooler build

What a Grizzly cold plunge is

A Grizzly cold plunge is a large rotomoulded hard cooler, made by Grizzly Coolers, used as a cold plunge tub. You sit in it with your knees bent and the water at your neck. A cooler is built to hold ice for days, so it makes a well-insulated tub with a gasketed lid, and its maker now sells it for the job: Grizzly’s pages say you can “sink into the 450 as an ice bath” and call the 350 “a full-body ice bath”.

It is one of the builds in the DIY cold plunge tub, and the tidiest, because nothing has to be sealed or framed.

We have not built one. The sizes are Grizzly’s, read on its site on 6 October 2026. Everything else comes from fourteen build threads on the r/coldplunge forum, dated 2023 to 2026.

Grizzly 350 or 450: the cold plunge cooler sizes

Grizzly sells two coolers big enough to sit in.

The number that decides it is the inside width. The 350 is 21.75 in wide inside, and commenters on r/coldplunge call that snug through the shoulders. One buyer, 5 ft 9 in and 195 lb, marked the width out against a wall, sat in it, and chose a wider tub. The 450 is nearly ten inches wider, and its owners say it has plenty of room.

Both are about 46 in long inside, which is under four feet. Nobody lies down in one.

The 350’s advantage is its 29 in outside width. Grizzly says it “fits through a standard doorway”. The 450 is 38.5 in wide and will not go through most inside doors. Other tubs are sized up in our guide to cold plunge dimensions.

The older Grizzly 400

Most build guides online are for the Grizzly 400, which is no longer in Grizzly’s catalogue. If you find one second-hand, two things differ. It has one drain, so the return hose needs a hole drilled through the wall. And a seller of plumbing kits for these coolers puts its insulation at about 1.5 in, against about 2.1 in for the 450. A 6 ft 4 in owner finds the 400 comfortable side to side and short for getting their head under.

Parts list for a cooler cold plunge

Parts with a button are on Amazon, whose prices we don’t print. Buy one cooler, not both. Here is one owner’s itemised list from 2024 for a 450: cooler $1,260, chiller $650, pump $105, filter housing $35, four cartridges $35, electrics $50, plumbing $70 and ozone $60, which comes to $2,265.

How owners plumb it

Some owners want both hoses on one side with the return high up, which means drilling a bulkhead through the wall. On a 450 the wall is about 2.1 in thick, and two owners say the bulkhead fitting used in the old 400 guides is too short for it. Both ordered a longer one made to size.

The Active Aqua 1/4 HP that most of these builds use removes 3,010 BTU an hour, by its maker’s spec. The maker recommends it for 40 to 92 gallons, which covers a 350 and falls short of a 450 filled to the brim, and approves it for indoor use only. Owners run it on both. How owners box and vent the chiller is in the DIY cold plunge chiller. If you are choosing one, the sums are in our guide to chiller sizing and our picks are in the best cold plunge chillers.

How well a cooler holds the cold

This is what you pay for, and owners back it.

One owner saw worse: a used 400 in a 65°F garage went from 37°F to 44°F overnight. The pipes and the filter had no insulation, and there was a puddle of condensation under them in the morning.

Without a chiller there is no filter either. The owner in Texas changed the water every couple of weeks until adding one.

What went wrong

• A 450 warped in the sun. One owner in Colorado says a new 450 warped within hours in direct sun, and that Grizzly agreed to replace it. One report, but keep yours in shade.
• Hot plumbing. An owner whose pump, filter and chiller sit in the sun saw the water rise from 40°F to 50°F in four hours of circulating.
• The lid seals too well. One 450 owner says the gasket pulls a vacuum and the lid takes real force to open.
• Lid height. A 450 with its lid swung fully open stands 61 in high, by one owner’s tape. Check for shelves and overhangs.
• Ozone in the wrong place. Put it after the chiller, on the return.
• Freezing weather. One owner left a 450 outside all winter with up to an inch of ice on the water and had no trouble. The advice in the same thread is to bring the chiller indoors before it freezes.

Is a cooler cold plunge worth it?

Against a stock tank build, no, not on price. The stock tank route in our DIY cold plunge tub guide comes to $1,000 to $1,300, and the difference is the cooler. A Grizzly costs $1,250 to $1,550 more than a 100 gallon tank.

What that buys is the insulation, a sealed lid and a tub that needs no frame, no foam and no sealant. Owners who chose it over a chest freezer say the same thing: nothing to sand, seal or rewire, and it cleans easily.

Against a finished tub it is closer. An owner in 2023 priced the ready-made version of this build at about $3,000 and saved $800 by building it. Another, at about $2,400, says they “probably spent more time doing it than the savings is worth”.

Buy a Grizzly for this if you want a hard, lidded, insulated tub outdoors and you enjoy plumbing. If you only want cold water tomorrow, start with a cold plunge in a bathtub or one of the cheap cold plunge tubs.

Common questions