Two questions arrive before anyone buys anything, usually after the first two minutes in cold water have convinced them. How cold should it be, and how long should I stay in.
A third one arrives about two weeks after delivery, usually at seven in the morning, and it is the angriest of the three: why is this thing running constantly and still showing 62°F.
Here are all three, with the actual numbers rather than somebody's morning routine.
How cold
45 to 59°F, which is 7 to 15°C. That is the band nearly every published trial sits inside. Colder is not automatically better and, more to the point, colder is not what was studied.
If you are starting, sit at the top of that range. 55 to 59°F is genuinely cold, entirely unpleasant for the first fifteen seconds, and far more likely to still be happening in March than 40°F is.
How long
The floor across the pooled trials was thirty seconds. Most protocols ran two to five minutes.
So thirty seconds counts. Two minutes is a solid session. Beyond about five minutes you are into territory the research has very little to say about, and the risk profile changes rather than the benefit growing.
Why your chiller cannot hold temperature
Four things decide whether a chiller keeps up.
- Volume. More water, more heat to move.
- Insulation. An insulated tub with a lid on is an entirely different job from an open one.
- Sun. An uninsulated tub catching afternoon sun can need a whole size more than the same tub in shade.
- Ambient temperature. A chiller in an 85°F backyard works considerably harder than one in a 60°F garage.
The mistake almost everyone makes is buying one size down. It runs constantly, never quite arrives, and feels faulty. It is not faulty, it is outmatched.
The ladder
| Tub | Output | Draw |
|---|---|---|
| Small, insulated, indoor | 5,000 BTU/hr | 3.9 A |
| Around 80 to 100 gallons | 7,500 BTU/hr | 3.9 A |
| Around 100 to 150 gallons | 10,000 BTU/hr | 7.2 A |
| Same, but pulls down faster | 11,500 BTU/hr | 7.2 A |
| Over about 150 gallons | 15,000 BTU/hr | 11 A |
Two of those deserve a note. The high efficiency units get more cooling out of an identical electrical draw: 5,750 BTU from the same 3.9 amps as the standard 5,000, and 11,500 from the same 7.2 amps as the standard 10,000. If the running cost matters more than the purchase price, that is where to look.
The electrical side is the easy part
Every chiller in the range runs on a standard 110 to 120 volt outlet, drawing between 3.9 and 11 amps depending on the unit. No electrician, no dedicated circuit, no 240 volt supply.
Two rules, though. Do not run one on an extension cord. And site it somewhere that can get wet, because they produce condensation.
The thing that kills chillers
They are outdoor rated above 32°F only. Below that they have to be disconnected and fully drained.
Water left standing in a titanium coil through a hard frost expands, and that is the end of the unit. It is a fifteen minute job in November and it is the single most common avoidable failure in this category.
Keeping the water clean
Cold water is not self-cleaning, it is just slow. A filter on the return catches hair and debris, and a washable 150 micron filter handles most of it. Some units add ozone sanitation, which reduces how often you drain.
The practical rhythm most owners settle into: skim anything floating before you get in, rinse before you get in rather than after, keep the lid on when it is not in use, and drain and refill on a schedule rather than when it looks bad.
Where we talk you out of something. Do not reflexively buy the biggest one. 15,000 BTU draws 11 amps, costs more every hour it runs, and at around 56 dBA it is not silent, which matters if the tub is under a bedroom window. A well insulated single-person plunge in a garage is held comfortably by the 7,500 BTU unit and you will barely notice it working. Oversizing is a quieter mistake than undersizing, but it is still a mistake. Tell us the volume, where it sits and how cold you want to hold it, and we will size it with you before you order rather than after.