How to Make Ice for an Ice Bath: Freezer Limits, Blocks and Bags

This page is about getting the ice. For how much you need, use the calculator and tables in how much ice for an ice bath; for machines, see the best ice makers for ice baths.

Your freezer is the bottleneck.

Every pound of water you freeze has to give up its heat through the freezer's coils, and a home freezer can only do that so fast. Amana's chest-freezer guidance is no more than 2 to 3 lb of unfrozen food per cubic foot of freezer space in 24 hours, and to let the freezer cool overnight before a big load. Load more and the freezer warms; Amana says it can then take several hours to stabilize. Applied to water, that sets a hard daily limit:

The guideline is written for food, and your own freezer's manual is the authority, but the takeaway holds: a freezer is a good place to store ice and a slow place to make it. For comparison, a 100 lb/day cube machine makes five to ten times what a 5 to 7 cubic foot freezer should freeze in a day.

Blocks or cubes: same cooling, different timing.

A pound of ice absorbs the same heat whatever its shape. Shape only changes how fast it gives that cooling to the water. A 6.3 lb block has about 200 to 220 square inches of surface. The same 6.3 lb as 0.9-inch machine cubes is about 260 cubes with roughly 1,270 square inches, about six times the surface. More surface melts faster.

• Cubes or crushed ice pull the temperature down fast, then they're gone.
• Blocks drop it slowly and keep working through a longer session or between sessions.
• Both together is the efficient routine: cubes or bagged ice to reach the target, a block or two to hold it.

So "blocks keep the plunge colder" is half true. They keep it colder for longer. They don't make it colder per pound.

Home methods, from best to worst.

1. Silicone block molds. The most ice per freezer slot and per minute of your time. The Haldane 4 pack below makes about 25 lb per batch. Fill a little short of the rim: water expands about 9% as it freezes.
2. Rigid food-grade jugs or bottles, frozen sealed. Leave about a tenth of the jug empty for expansion. You can drop sealed jugs straight into the tub: the meltwater stays inside, which keeps your water care steady and keeps debris out, and you refreeze them. They chill more slowly than loose ice because the plastic sits between the ice and the water. Never use glass in a tub you sit in.
3. Flat zip-top freezer bags. Slabs stack well and freeze faster than one deep container, because they're thin. Double-bag them; a split bag in the freezer is a sheet of ice on everything else.
4. Ice cube trays. Fine for drinks. For a tub, the number of trays and hours makes them a non-starter.
5. Balloons. Skip them. They can burst in the freezer, each one holds far less than a mold, and you end up fishing bits of latex out of the tub.

Getting ice without making it.

Bagged ice is the simplest supply for one or two plunges a week. Read the bag: Reddy Ice sells 5, 7 and 16 lb bags, and Home City Ice sells a 20 lb bag. A 100-gallon chill from 60 to 50°F is about eight 7 lb bags or three 20 lb bags.

An ice machine makes sense once you're buying bags every few days. The catch is the bin, which on these machines is not refrigerated. A machine whose bin holds about one full chill saves the most handling.

Store it so it lasts.

• Bag it. Machine ice fuses into a slab in the bin; bagging it in 10 lb units keeps it easy to handle and makes your ice math simple.
• Use the freezer for storage, not production. Ice that's already frozen adds little load: cooling it from 32 to 0°F takes about a tenth of the energy it took to freeze it. Bagged ice and finished blocks can fill the space.
• Older freezer ice is a little stronger. Ice at 0°F absorbs about 10% more heat per pound, on its way to becoming 50°F water, than ice at 32°F. That's the real size of the "let your ice age in the freezer" tip: worth having, not worth planning around.
• Keep it out of the sun until you use it. A cooler in the shade holds a session's worth of bags while you set up.

When to stop making ice.

Add up a week. A 100-gallon tub kept full and topped up 4°F a day uses about 145 lb of ice; refilled from 60°F every day it's about 360 lb. A big chest freezer doing nothing else can about keep up with the top-up routine; no home freezer keeps up with daily refills. At that point the choice is a cube machine with a drain, or a chiller that cools the water directly. Sauna Marketplace sells the Coldture Water Chiller Pro and a Penguin chiller kit, and our chiller sizing guide shows what a tub needs.

FAQ

How do I make ice for an ice bath at home?

Freeze water in large silicone block molds or rigid jugs a few days ahead, no more than 2 to 3 lb of water per cubic foot of freezer per day. Bag and store it until you have enough for one chill.

What's the best way to make lots of ice for an ice bath?

For more than about 20 lb a day, a cube ice machine with a big bin is far faster than a typical home freezer. For a few bags a week, buying bagged ice is simpler than making it.

Are ice blocks better than ice cubes for an ice bath?

Per pound they cool the same. Cubes chill faster; blocks melt slower and hold the temperature longer, so a mix works well: cubes to get down, a block to stay there.

How long does a 6 lb ice block take to freeze?

The Haldane molds list 12 to 24 hours. Expect the long end or more in a full freezer or with several molds at once.

Can I freeze water bottles for an ice bath?

Yes, in rigid plastic with about a tenth left empty for expansion. Sealed bottles keep meltwater out of the tub and can be refrozen, but they chill slower than loose ice. Never use glass.

How much ice can my freezer make in a day?

About 2 to 3 lb of water per cubic foot, based on Amana's guidance for adding unfrozen food to a chest freezer. A 7 cubic foot chest freezer handles about 14 to 21 lb a day.