The kind of chiller you need for your cold plunge depends on a several factors: how cold you want your plunge to get, whether you set it up indoors or outdoors, how hot a climate you live in, how often your plunge will be used, and how many people will be using it regularly.
Our ¼ horsepower tub cools to 39 degrees in optimal conditions(indoors, or outdoors if stored under cover, protected from the elements, and kept away from direct sunlight), has a cooling speed of 1-4 degrees per hour, and can accommodate 3-4 people per day.