Keep Your Water Cold
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The Initial Cool-Down
Before we discuss the options for keeping your water cold, I’d like to offer a practical suggestion for the initial cool-down: use ice. Chest freezers are efficient, but they are not fast. While you can just let your chest freezer do the work, it could take several days of continously running.
Adding ice for your first time cool down, and on refills after cleaning and maintenance saves wear on your equipment and extends the compressor’s life. How much ice is needed depends upon the initial water temperature, your target water temperature, and volume of water. See my free ice bath calculator here:
https://chestfreezercoldplunge.com/icebathcalc/
Overview
One of the best things about having your own cold plunge is being able to use it whenever you want, without having to think about it. That means keeping your water consistently within your preferred temperature range.
If you have a chiller-based cold plunge, your chiller already has a built-in temperature controller, so you don’t need an external one. But if you’re converting a chest freezer into a cold plunge, you’ll need a way to control its cooling. The chest freezer’s built-in thermometer is great for keeping your food frozen, but is not suitable for cold plunge use.
There are three basic approaches.
1. Manually Plugging and Unplugging
This is the simplest option, and it doesn’t cost anything. Just plug in your freezer when you want to cool the water and unplug it when it’s cold enough. You’ll need a separate thermometer.
The problem? Unless you’re diligently monitoring the temperature, your water can end up too warm or, worse, frozen into a solid block of ice. Neither accomplishes your goal.
I don’t recommend this method.
2. Using a Timer
A timer allows your chest freezer to run at specific times of the day. This can be useful if you’re operating on solar power or have other reasons to limit when your freezer runs.
The challenge is that cooling needs vary depending on ambient temperature, pump operation, and frequency of use.
You might get everything dialed in during the summer, only to need to readjust it when the weather changes. If you live in a climate with wide swings in temperature or humidity, this can become problematic.
Some people use an old-school mechanical timer with a dial. It would be best to use a timer that is programmable with days of the week and can keep the time if the power goes out. You’ll need to find one that is rated for use with an appliance.
For most people, a timer creates more work than necessary.
3. Using a Temperature Controller (Recommended)
A temperature controller automatically turns your chest freezer on and off to maintain your desired water temperature.
This is by far my preferred approach. Once properly configured, it keeps your cold plunge ready whenever you are.
Here are three controllers I recommend, depending on your budget and needs.
Inkbird – Best Budget Option
The Inkbird ITC-308 is an inexpensive, popular temperature controller. It’s available in both standard and Wi-Fi versions. Keep in mind that these controllers can and do fail- some sooner than later.
- Inkbird ITC-308 – Standard: https://amzn.to/3DF2A6h
- Inkbird ITC-308 – Wi-Fi: https://amzn.to/35tgbBR
Be sure to purchase the version with the silicone-covered temperature probe. Although Inkbird rates its metal probe as waterproof, I’ve seen too many failures involving prolonged underwater use to recommend it.
We’ve also seen controller failures even with the correct probe. In some cases, a failure can leave the freezer running continuously.
That’s a serious concern. As ice forms, the compressor may continue working, and expanding ice can crack the liner or damage the freezer walls and interior components. Sometimes the damage can be subtle. You may not notice a small crack, but that can lead to water getting inside of the chest freezer walls. The result can be catastrophic failure.
Inkbird provides a one-year warranty, so if it fails within that time, contact the manufacturer about a replacement. Given the low price, purchasing a new unit is often the most practical solution once the warranty expires.
The Wi-Fi version is convenient because it makes programming easier, but remote control isn’t particularly necessary for most people.
Watch my YouTUbe video on programming the Inkbird:
https://youtu.be/tSmU7nSQBnw
Aqua Logic – Best Dedicated Temperature Controller
Aqua Logic Temperature Controller:
https://amzn.to/4hAZOSy
Aqua Logic manufactures professional-grade temperature controllers for aquariums and other aquatic applications.
This was the very first piece of extra equipment I purchased for my chest freezer cold plunge. I used it for seven years without a single failure. I’ve recommended it to countless people over the years, and have not seen a single report of a failure.
It’s also considerably easier to program than the standard Inkbird.
If you want a high-quality, dependable controller without additional bells and whistles, this is an excellent choice.
CP Brain – Best All-in-One Control System
CP Brain: https://www.cpbrain.com/
Use discount code JOHN for 10% off.
The CP Brain was developed by a member of my Chest Freezer Cold Plunge Facebook community. I’ve been using one since 2025, and it’s an excellent solution for people who want more than temperature control.
In addition to controlling your freezer, it includes programmable outlets for scheduling pumps and other equipment, a built-in ozone generator, and an optional lid safety sensor.
It costs more than a basic temperature controller, but it can replace several separate devices and simplify your overall setup.
Watch my CP Brain video review:
How to Set Your Temperature Controller
There are two important settings:
Target Temperature: The temperature you want your water to reach.
Differential (also called hysteresis or deadband): How many degrees the water can warm up before your freezer turns back on.
For example, with a target of 45°F and a differential of 2°F, the freezer turns off at 45°F and turns back on when the water reaches 47°F.
My recommendation is a 2°F differential (approximately 1.1°C).
A 1°F differential can cause excessive cycling of your compressor. A 3°F differential creates wider temperature swings and longer cooling cycles. Most people use somewhere between 1°F and 3°F, but I wouldn’t recommend exceeding 4°F.
Fail-Safe: Use an Independent Temperature Alarm
Regardless of which temperature controller you choose, I strongly recommend installing a completely separate temperature sensor with high and low alarms.
I’ve seen too many failures that could have been prevented from becoming catastrophic with an early warning.
Here’s the independent Wi-Fi temperature alarm I’ve been using:
Set your alarm thresholds a couple of degrees outside your normal operating range. For example, if your target is 45°F with a 2°F differential, you might set your low alarm to 43°F and your high alarm to 49°F.
If your controller fails and the water begins cooling or warming, you’ll have an opportunity to catch the problem before it becomes serious.
Final Thoughts
The goal is simple: Keep your cold plunge consistently cold, easy to maintain, and ready whenever you are.
Choose a controller that meets your needs, use an independent temperature alarm, and eliminate as much unnecessary maintenance as possible.
And remember, before entering your chest freezer cold plunge, always disconnect the electrical power. Read my important article on unplugging your cold plunge:
https://chestfreezercoldplunge.com/unplug/
For guidance on choosing your water temperature and how long to stay in, read my article “How Cold and How Long?”