Hot Tub Temperature: What to Set and Why 104°F Is the Limit
Keep hot tub water at 104 °F or lower: that is the upper limit from both the U.S. Consumer Product Safety Commission (CPSC) and the CDC. Lower settings are fine; pick the lowest one you find comfortable. Children, pregnant people, and anyone who has a heart or blood pressure condition or takes medicine that can cause drowsiness need extra caution, as covered below.
On this page (8 sections)
This page covers what the public-health sources say about temperature, how to check that the temperature on the display is accurate, and how warm water changes your water care. It is general information, not medical advice. For questions about your own health, ask a doctor.
The upper limit: 104 °F
The CPSC has warned since 1979 that hot tub water should never exceed 104 °F (40 °C). The CDC's hot tub guidance gives the same limit.
Why it matters: soaking in water hotter than your body raises your body temperature. The CPSC warns that this can cause drowsiness, which can lead to unconsciousness and drowning. It also warns that water at 106 °F can raise body temperature to the point of heat stroke, which can be fatal even for healthy adults. Alcohol makes drowsiness and drowning more likely.
So 104 °F is a ceiling, not a target. Nothing requires you to run that hot.
What to set: a starting point by situation
There is no single "best" temperature. Pick the lowest setting you find comfortable, within the limits below:
| Who or when | What the sources say | Source |
|---|---|---|
| Anyone | Never above 104 °F | CPSC, CDC |
| Healthy adults | 100 °F was "considered safe for a healthy adult" in the CPSC's 1979 warning | CPSC (1979) |
| Children under 5 | Don't let them use hot tubs | CDC |
| Older children | Special caution; constant adult supervision near hot tubs | CPSC |
| During pregnancy | Talk to a healthcare provider before using a hot tub. The CPSC warned in 1979 that water above 102 °F early in pregnancy may harm the baby. | CDC, CPSC (1979) |
| Heart disease, diabetes, blood pressure problems, circulation problems | Check with a doctor before using a hot tub | CPSC (1979) |
| Taking medicine that can cause drowsiness | The CPSC's 1979 warning says not to use hot tubs; ask your doctor or pharmacist | CPSC (1979) |
| After drinking alcohol | Don't soak; alcohol raises the risk of drowning | CPSC |
The CPSC guidance on healthy adults, pregnancy, medical conditions, and medicines comes from its 1979 warning, which is still published on cpsc.gov. Medical advice has changed in many areas since then, so treat it as background. Your doctor's advice takes priority over any table here.
Pregnancy, children, and medical conditions
Pregnancy. The CDC's advice is short: if you are pregnant, talk to a healthcare provider before using a hot tub. The CPSC's older warning says soaking in water above 102 °F during the first three months of pregnancy can cause fetal damage. We don't suggest a "pregnancy setting." Ask your provider.
Children. The CDC says not to let children under 5 use hot tubs. For older children, the CPSC asks for special caution and constant adult supervision. The CPSC also warns about drowning and about hair getting caught in suction fittings, so keep children away from the tub unless an adult is watching.
Medical conditions and medicines. The CPSC names heart disease, circulatory problems, diabetes, and blood pressure problems as reasons to check with a doctor first, and drowsiness-causing medicines as a reason not to soak. If you take regular medicine, ask your doctor or pharmacist whether hot water is a problem for you.
Check the real temperature
The number on the control panel is the heater's reading, not always the water's. The CPSC notes that hot tub thermostats can be off by as much as 4 °F, and suggests checking with an accurate thermometer before you get in.
- Use a floating pool and spa thermometer or a digital probe, and check after the jets have run for a few minutes so the water is mixed.
- If the reading is higher than the setpoint, turn the setpoint down until the water reads 104 °F or lower, and have the heater checked.
- If the water won't reach the setpoint, or drops overnight, see hot tub not heating.
Temperature and sanitizer
Hot water makes water care harder. The CDC notes that higher hot tub temperatures dissipate chlorine rapidly, so sanitizer needs closer watching than in a pool. Lowering the temperature a few degrees does not make the water germ-free: the CDC lists 77–113 °F as the range most favorable for Legionella growth, and normal hot tub settings sit inside it.
What that means for you:
- Test sanitizer and pH before each soak in a busy week. The CDC ranges are at least 3 ppm free chlorine, or 4–8 ppm bromine, and pH 7.0–7.8.
- Expect to add chlorine more often when the tub is hot and used daily. The hot tub chlorine calculator works out each top-up for your gallons.
- Keep stabilizer (CYA) out of the tub, as the CDC recommends, and change the water on a schedule. The water change calculator estimates how often.
- Itchy skin after soaking can be a water problem; see hot tub rash for what to check.
Winter and summer settings
Winter. Cold air makes the water feel cooler on your shoulders, but the 104 °F limit doesn't change. Keep the cover on between soaks; it holds in heat and keeps debris out. In freezing weather, follow the freeze-protection guidance in your hot tub's manual before you turn the heater down or leave a filled tub unused.
Summer. Many owners lower the setpoint on hot days so a soak cools them down instead of heating them up. A lower setting also means less heater run time. Sanitizer still breaks down quickly in warm water, so keep testing.
What one degree costs to heat. The calculator below starts with a 1 °F rise in a 400-gallon tub with a 4 kW heater, an example size. It takes about 1 kWh, roughly 15 minutes of heating, and about $0.17 at the example electricity rate. That is heat-up math only: an open cover, cold air, and wind add heat loss on top. Enter your own tub size, heater power, and rate from your bill.
Away for a while. Your manual may have an economy or vacation mode that holds the water at a lower temperature. Keep circulation and sanitizer going while the tub sits, then bring the temperature back up and test before anyone soaks.
The full routine is on hot tub maintenance.
Health and safety. Pooldex does not give medical advice. Ask a doctor before using a hot tub if you are pregnant, have a medical condition, or take regular medicine. Keep water at 104 °F or lower, never soak after drinking alcohol, and watch children at all times. Get out right away if you feel dizzy, sleepy, or sick. Leave heater, wiring, and control-box repairs to a qualified electrician or hot tub technician, and follow your manual's electrical safety directions. Follow your sanitizer's label and never mix chemicals. In an emergency, call 911; for chemical exposure, call Poison Control at 1-800-222-1222.
FAQ
Is 104 too hot for a hot tub?
104 °F is the upper limit from the CPSC and the CDC, not a recommended setting. Lower settings are fine. Children, pregnant people, and people with some medical conditions need extra caution; ask a doctor.
What temperature should a hot tub be for kids?
The CDC says children under 5 should not use hot tubs. For older children, the CPSC asks for special caution and constant supervision. Ask your child's doctor about a specific temperature and soaking time.
Can you use a hot tub while pregnant?
The CDC says to talk to a healthcare provider first. The CPSC warned in 1979 that water above 102 °F early in pregnancy may harm the baby. Follow your provider's advice.
Should I turn my hot tub down in the summer?
Many owners do, for comfort and to cut heater run time. Any setting at or below 104 °F is within the CPSC and CDC limit. Keep testing sanitizer, since warm water uses it up quickly.
Sources
- U.S. Consumer Product Safety Commission, CPSC warns of hot tub temperatures (1979: 104 °F limit, 100 °F for healthy adults, pregnancy, medical conditions, medicines, alcohol, thermostats off by up to 4 °F): cpsc.gov
- U.S. Consumer Product Safety Commission, CPSC issues warning for pools, spas and hot tubs (1996: 104 °F, alcohol, supervision of young children, hair entrapment): cpsc.gov
- CDC, What you can do to stay healthy in hot tubs (104 °F, children under 5, pregnancy, chlorine, bromine, pH): cdc.gov
- CDC, MMWR 2000, Pseudomonas dermatitis/folliculitis associated with pools and hot tubs (higher temperatures dissipate chlorine rapidly): cdc.gov
- CDC, Controlling Legionella in hot tubs (77–113 °F growth range): cdc.gov
- CDC, Home pool and hot tub water treatment and testing (no CYA in hot tubs): cdc.gov