Chillers – How to Size a Chiller for Your DIY Cold Plunge
Introduction
If you have been thinking about building a cold plunge for home, or (especially) commercial use, correctly sizing the chiller is essential.
A chiller is like the heart of your DIY cold plunge, and sizing it correctly will make the difference between a setup that you love and one that disappoints.
An undersized chiller will not be able to keep your water cold enough, or if it does, it will run constantly, becoming very expensive to operate.
A significantly oversized chiller will keep your water cold, but it may be more expensive than what is necessary.
The best practice is to size a chiller based on the worst-case use scenario. That means keeping the water at your target temperature during the hottest summer months.
When in doubt, get the next bigger-sized chiller!
I am an official reseller for Penguin Chillers, and if you’re in North America and looking for a new chiller, I can help you with sizing.
Most chillers are advertised with HP, which is horsepower. However, HP will not tell you how fast a chiller can actually cool the water or the coldest temperature it can reach.
When shopping for a chiller, there are a few key ratings to look at.
- The coldest possible temperature
- The BTU rating, and
- The power used (watts and amps).
Keep in mind that the coldest temperature listed is in IDEAL conditions. The following variables impact a chiller’s performance, regardless of its temperature range and BTUs.
For more information about BTUs, see this article:
For cold plunges, chillers below 1/4 HP are not recommended because they generally will not get your water cold enough and will have to run very frequently to work at all, which not only makes them more expensive, but also shortens their life span.
Also, keep in mind that the quality of chillers, including how they are designed and the materials used, can make a significant difference.
How Chillers are Rated
In the consumer market, chillers are typically rated with HP (Horsepower). However HP does not tell you how much (or how well) a chiller will work.
The number to look at is the BTU rating of the chiller. BTU stands for British Thermal Units, which is defined as “the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.” If you have a gas grill for your outdoor summer cookouts, you’ll know it is rated in BTUs.
BTUs are also used to measure how much heat can be removed from water with a chiller. Two chillers with the same HP might have very different BTU rating.
Keep in mind that some chillers might perform slightly or significantly lower than their listed BTU rating. Penguin has tested countless chillers from other manufacturers over the years. Some very popular brands have performed as much as 20-25% below their rated BTU.
Questions to Ask
Here are the questions I ask my clients to determine the best chiller for their cold plunge.
- What size (volume) tank do you have?
This is a good place to start, but is ONLY the starting variable. Most DIY cold plunges use tanks with fewer than 400 gallons. If that is the case, the general guidelines are below, but definitely consider all of the other variables if you don’t want to end up with a chiller that performs poorly.
50 – 200: 1/4 HP to 1 HP
200 – 400: 1 HP to 1.5 HP
400 – 600: 1.5 to 2.5 HP
600 – 1,000: 2.5 HP+ - What material is the tank made of (plastic, metal, etc.)
This variable is not critical, but it does make a difference if your tank is not insulated. Metal transfers heat much faster than plastic. If your tank is uninsulated and gets direct sun exposure, the water will heat up faster in a metal tank than in a plastic tank. - Is your tank insulated? If yes, what kind of insulation did you use, how thick is it, and how was it applied?
2 – 3 inches of insulation is recommended. The highest standard is a 2-part, closed-cell, high-density spray foam insulation with moisture/vapor barrier properties. Going with the next higher-sized chiller will help if your tank is not insulated, especially with direct sun exposure. If you’ve used Great Stuff (the spray can from local hardware stores) to insulate your tank, go with the next size up. - What is your target water temperature?
Not all chillers are capable of cooling to the same temperature. Some aquarium chillers have a low temperature rating of 50 – 55°F. Others are in the 40°F range, and some can bring the water to 34 – 39°F.
The low temperature range needed depends on your goals and how the cold plunge will be used.
Remember that a chiller’s temperature range is given under “ideal conditions.” Anything less than ideal can result in warmer water temperatures. - Where will your cold plunge be located indoors (spare bedroom, studio, retail facility, etc.) or outdoors (garage, covered patio, backyard, etc.)?
There can be a significant difference between having your chiller inside and outside. All chillers work on a performance curve with regard to the ambient temperature. Usually the sweet spot in the bell curve is between 70 – 78°F. When it is either warmer or (ironically) colder than that range, the chiller must work harder. - Here are additional questions to ask about your cold plunge location:
a. What is the highest temperature during the hottest month of the year?
b. What is the lowest temperature during the coldest month of the year?
c. What is the average humidity during the hot months?
d. How many hours of direct sunlight will your cold plunge receive?
A chiller outside in Arizona during July will perform very differently from a chiller inside a climate-controlled room. A chiller outdoors in central Texas or south Louisiana (locations with high humidity) will perform very differently than a chiller in northern California, where the humidity is much lower.
If you have temperatures regularly above 80°F, a 1/2 HP or 3/4 HP chiller is a good place to start. - Regarding the usage of your cold plunge:
a. What time of day will it be used? (mornings, afternoons, evenings, etc.)
b. How many people will be using it, and for how long?
c. Will you use your chiller as part of a contrast therapy protocol with a sauna or hot tub?
If your cold plunge is outside and you only use it once daily in the morning, the relatively cooler evening temperature will help the chiller do its job. If you use your cold plunge several times throughout the day when temperatures are generally warmer, going with the next-sized chiller is a good idea.
Each person using a cold plunge can increase the water temperature by 1 – 2 (or more!) degrees F. If you have many people plunging within a short time, having a more powerful chiller will help keep the water closer to your desired temperature.
If you plan to do many rounds of contrast therapy, a more powerful chiller will be helpful. I’ve seen the water temperature in a tub with a low-powered chiller increase by 10 degrees F after 40 minutes of several rounds of going directly between a traditional Finnish sauna and the cold plunge.
I stopped by a local facility in Austin to see their contrast therapy setup with a cold plunge and sauna. Someone had just finished a 45-minute session. The temperature in the Mozoko Forge (which was set to 33°F) was at 45°F after several rounds of the person going back and forth between the sauna. The Morozko uses a chest freezer compressor, which is not anywhere near as powerful (or fast) as a chiller, but also keep in mind that chillers do take time to bring down the water temperature. Most chillers I’ve seen in commercial settings over the years are seriously undersized.
If you plan to have many people using the cold plunge throughout the day, especially with contrast therapy, you’ll need a chiller powerful enough to bring the water back to baseline fast enough between each scheduled time. - How far away from the tank will your chiller be located?
The best practice for simple DIY cold plunges is to keep the chiller, pump, and filter as close to the tank as possible. If you are building a permanent tank (ex., pouring concrete or using masonry), you might prefer to have your equipment farther away. If it is more than 10 feet away, you’ll need to consider the pipe size and how well it will be insulated. - Do you have a plan for your pump/filter yet? If yes, which ones are you using?
All pumps will have a certain flow rate (gallons per minute/hour) and a certain amount of pressure that they create, which is measured in pounds per square inch (PSI).
All chillers have minimum and maximum flow rates in order to work correctly. If the flow rate is too low or too high, the chiller will not work efficiently or at all. With Penguin Chillers, we know that a flow rate between 500 gph to 1,800 gph will work.
Chillers also have a maximum pressure limit. Too much pressure (for example, using some pumps meant for swimming pools) can damage the chiller. The Danner pumps recommended above all work with Penguin Chillers.
If you want to use a different pump than Danner with a Penguin Chiller, please contact us so that we can make sure the flow rate and pressure will work.
Penguin Chillers
Penguin Chillers are designed, built, and serviced in the US. They range from 1/2 HP up to 2.5 HP for the consumer market. More powerful chillers are available for commercial applications. Countless hundreds of people in the US and Canada are using Penguin chillers for their DIY cold plunges.
If you decide to buy a Penguin Chiller from me, you’ll receive the same price, service, lead time, and warranty as you would buying directly from Penguin. You’ll also receive my help in answering questions about designing and setting up your system. Your patronage helps me support our global cold plunge community- and my family- and is appreciated.
You can find more information about Penguin chillers and links to pricing here:
https://ChestFreezerColdPlunge.com/chillers
If you have specific questions, fill out the contact form (see the main navigation menu at the top).