If you’ve just purchased a hot tub, or simply have a few questions as to how to regulate the water temperature, you’re in the right place.
In this blog post, I hope to answer a few common questions as they relate to the temperature of the water in your hot tub.
Table of Contents
- The maximum temperature for a hot tub
- What’s too hot?
- What’s too cold?
- What’s the ideal hot tub temperature?
- Winter vs. summer temps
- Daytime vs. nighttime temps
- Temps to conserve energy when not in use
- Why you should never turn your hot tub off
What is the maximum temperature for a hot tub?
104° Fahrenheit is the maximum hot tub temperature limit according to guidelines set by both the CDC and Consumer Product Safety Commission (CPSC). 104° Fahrenheit is the maximum temperature hot tub manufacturers set for UL-certified hot tubs on the market.
For healthy adults, you shouldn’t exceed a maximum hot tub temperature of 104° Fahrenheit, even if for some reason your hot tub model has the ability to do so.
The dangers of staying in a hot tub that’s too hot
If your hot tub is too hot, this can cause you to feel light-headed, dizzy, or nauseous.
Prolonged exposure to temperatures of 110° Fahrenheit and above can cause death through what’s called hyperthermia, which could lead to fainting or heat stroke.
Nothing to mess with, which is why we’ve seen more hot tub temperature regulation over the past 20 years.
People who should avoid high hot tub temperatures
- Small children: Some sources recommend that children under five years old should not be allowed in water over 95° Fahrenheit, and keeping kids out of a hot tub is a good idea in general.
- Pregnant women should avoid higher water temperatures to prevent possible harm to the fetus.
- People with high blood pressure
- People with heart conditions
What are hot tub high limit switches?
Modern hot tubs have what are called high limit switches that will automatically shut off your hot tub’s heater to prevent the temperatures from exceeding 120° Farenheit.
What causes an HL error code on a hot tub?
A hot tub will likely flash an ‘HL’ error code if the HL switch senses water approaching 112° Farenheit; If the heater barrel reaches 120° Farenheit, the code will display permanently (for makers like Arctic Spas) until the water cools off.
An HL error code can be due to a blockage around the heat pump or filter; if water can’t circulate, or your cover is insulating a little too well on a hot day, this can cause your hot tub to overheat.
Never use a hot tub if these error codes are showing. This is not to say that people don’t attempt to remove these chips to exceed that number by a few degrees, but it is not recommended and can likely void your warranty.
Hot tub thermometers
If you ever want a better gauge of your hot tub temperature, another idea is to purchase a separate water thermometer like this.
These are great, especially for older hot tubs where the sensor may not always be giving an accurate reading.
What is the minimum temperature for hot tubs?
In general, the minimum temperature for most hot tub manufacturers is somewhere around 85° to 90° Fahrenheit.
While most people feel comfortable with temperatures between 100° and 104° Fahrenheit, in the summers when it’s hot, you can set it at a lower temperature.
Most heaters have settings as low as 80°. For a temperature below that, you have to either turn off the heater and let the hot tub cool naturally (assuming the ambient temperature is below that) or cool the water using a cooling system I’ll discuss below.
What’s the ideal hot tub temperature?
A safe hot tub water temperature for adults is anywhere in the 99° Fahrenheit to 102° Fahrenheit range under normal conditions. Most hot tubs
This ultimately depends on personal preference, with many people opting for lower temperature settings in the summer vs. winter months.
Hot tub temperatures in winter vs. summer
In the wintertime, as a general rule, it’s typically much more efficient to leave your hot tub somewhere around 95° Fahrenheit when not in use.
However, during the summer many people use their hot tub for cooling off.
If you prefer a lower temperature during the summer months, a good range is generally 85°-95° Fahrenheit. This will be noticeably cooler than your body temperature of 98.6°
Operating your hot tub in the summer hot or cold!
While setting your hot tub on a lower setting is one thing, you can actually hook up a cooling system designed for hot tubs like this one, specially designed to cool as well as heat your spa.
As seen in the video above, this system can chill the water as low as 60° Fahrenheit as well as work with the spa’s heater to heat the water more quickly.
Heat pumps are more energy-efficient than the electrical heater on most spas, so you might want to use that alone unless you’re in a hurry to heat the water.
You could also throw some ice into the hot tub to bring the water temperature down. This will not harm the equipment.
Daytime vs. nighttime hot tub temperatures
The only difference in an ideal daytime vs. nighttime hot tub temperature is the ambient air temperature.
Unless there are drastic swings in temperature between daytime and nighttime, you should be fine with leaving your hot tub at the same temperature both during the day and at night.
What temperature should you leave your hot tub on when not in use?
The simple answer: When your hot tub is not in use, the amount of money saved maintaining a higher temperature is actually cheaper than the cost of turning the temperature down, and having to re-heat the water 10-20°.
While it may sound like common sense to turn your hot tub down every time it is not in use, it’s actually better to maintain a constant soaking temperature, which is typically around 100° Fahrenheit for many people.
The 5° rule
When not in use, as a general rule of thumb, keeping it within 5° of your preferred temperature is a good idea. Insulating the spa with a cover can also help to reduce costs.
If you keep your spa heated all the time, it will use the least energy when it is at the same temperature as the surrounding air temperature, if that’s warm enough for you. Which it probably isn’t.
Since many modern (and efficient) hot tubs have the ability to raise the temperature of water 3° to 10° Fahrenheit per hour, this could easily take 3-4 hours or longer to heat up to optimal temperatures of 100°-102° that many people prefer.
The heating time really depends on the size of your hot tub and how efficient it is at heating water.
Conserve energy with a thermal hot tub cover
Maintaining a constant temperature is often easier than people think since a good hot tub cover will help to conserve energy anyway.
With an effective thermal cover in place, you’ll get a feel for how quickly the hot tub cools down and how quickly it heats up. Then you can use that knowledge to guide your evaluation of the trade-off between convenience and energy use.
A thick foam cover like the one pictured above I found on Amazon here does an excellent job of insulating the water and preventing evaporation, which cools the water.
Insulating with a hot tub bubble cover
You could also add a soft floating membrane like this one to minimize evaporation and protect the underside of the spa cover from possible chemical damage.
If you use your hot tub often, thermal protection and insulation can help to reduce energy bills, but it really comes down to convenience for most people.
What temperature is too low for hot tubs?
Since most hot tubs have an economy mode, the lowest temperature you will want to maintain is around 85-90° at all times.
Keep in mind, that you’ll want to completely drain the hot tub if you intend not to use it for 4 to 5 months at the time, for example.
Why you should never leave your hot tub turned off
Without circulating water, algae and bacteria can grow if you simply leave your hot tub off, which is something you never want to do unless you are repairing it.
For this reason, hot tubs will circulate water (even on their lowest setting), which really prevents this from occurring. Of course, you’ll always have to maintain your chlorine and cleaning regimen for safe use.
In general, you really don’t want to vary the temperature in your hot tub all that often in order to safe on costs.
Most people pay somewhere in the $1 per day range to operate their hot tub, and with the technology out there, there’s really no need to worry all that much about the temperature you are maintaining.
I hope this post helped answer a few of your temperature-related questions.
Check out my post 15 Best Outdoor Hot Tub Accessories for a few ideas I thought were pretty cool (no pun intended). Be safe and have fun!
This post was updated on July 15, 2022 to reflect industry best practices.