Hot tub temperature
A healthy adult should set the hot tub temperature between 100 and 104°F (38 to 40°C), with 104°F (40°C) as the absolute maximum. You should choose cooler water for kids, when pregnant, or for extended soaks.
- Upper limit, never go above
- 104°F (40°C)
- For healthy adults
- 100°F to 104°F (38°C to 40°C)
- If a doctor approves, most spa manuals allow use during pregnancy
- 100°F (38°C)
- Time to soak before lowering heat
- 10 minutes
Hot tub temperature chart
| Water | Good for | Limits |
|---|---|---|
| 110°F (43°C) | Unsafe for anyone | Deaths reported at about this heat |
| 104°F (40°C) | A short soak for a healthy adult | The top limit: never go higher |
| 100°F to 104°F (38°C to 40°C) | Most healthy adults | Go cooler after 10 minutes |
| 100°F (38°C) | Longer soaks | Pregnant users should stay in no more than 10 minutes, and only with doctor approval |
| Under 100°F (38°C) | Young children | Ask a doctor first; an adult always watching |
Warnings in spa owner's manuals and the CPSC, the US product safety agency, are the sources of these limits.
Max hot tub temperature: 104°F (40°C)
The CPSC recommends keeping spa water at 104°F or below. They helped make rules so spa controls never let water pass that point.
Water that is very hot makes you drowsy, so you might pass out and slip under. The CPSC reports several deaths in water near 110°F (43°C).
Public hot tubs follow this same rule. The CDC instructs operators to keep water at or below 104°F (40°C).
Your display might read wrong. Use a separate thermometer to check the water before entering.
Ideal hot tub temperature for adults
For a healthy adult, spa manuals give the safe range as 100 to 104°F, or 38 to 40°C. Choose a hot tub temperature within that range that feels comfortable to you.
Lay-Z-Spa held water at 38 to 40°C to test running costs, so this band fits an inflatable tub too.
Keeping one temperature usually saves money compared to cooling the water then reheating it, if you use the tub most days. Use the running cost calculator to see how your usage affects costs.
Limits on soak time
- Turn the heat down after 10 minutes. The Intex manual says to use lower heat for longer soaks.
- If dizzy, sleepy, or too hot, get out right away. Overheating starts with these signs.
- Do not drink alcohol before or while soaking. The CPSC warns that doing so can cause drowning.
- Do not soak by yourself so someone is there to help if you feel faint.
Your body overheats once it rises a few degrees above the normal 98.6°F (37°C). Hyperthermia is what doctors call it.
Hot tub temperature when pregnant, and for children
Young children and pregnant women should discuss spa use with a doctor first, the CPSC states.
With a doctor's okay, spa manuals say the most you should use in pregnancy is 100°F (38°C) for no more than 10 minutes. Your doctor might recommend even less time or lower heat, because high temperatures early in pregnancy can hurt the baby.
While asking for cooler water for young children, manuals offer no specific number. Keep the cover locked when unused, and ensure an adult watches them always.
Hot tub temperature in summer and winter
All year long, the cap stays at 104°F (40°C). How hard it is to hold your set number changes with the season.
On hot days, pumps alone can warm water past your setting. For this reason, the Hot Spring owner's manual includes a Summer Mode that turns off the heater and circulation pump for eight hours daily to reduce heat gain. When 100°F (38°C) feels too warm, lower the water by a few degrees. Choose a morning or late evening soak, when the day is cooler.
During winter, leave the tub running and keep the cover on. Hot Spring warns that the spa will freeze if Summer Mode stays on below 32°F (0°C), and its warranty excludes such damage. A bigger running cost and a longer heat-up time are what to expect in cold months.
Common questions
Is a hot tub too hot at 104?
No, a healthy adult can safely go up to 104°F (40°C), but keep those soaks short. The water never goes past it because spa controls are built that way.
How high can the heat get in an inflatable hot tub?
Heaters from Lay-Z-Spa, Bestway and Intex all top out at 40°C (104°F). Hard tubs have the same top limit.
Does my hot tub display show the right temperature?
Sometimes it is wrong. Before you get in, the Intex manual warns you to check with an accurate thermometer because heater controls vary.
Should I lower my hot tub temperature when I am not using it?
Keep the setting steady if you soak 3 or more times weekly. Lay-Z-Spa says reheating takes more energy than keeping the water warm.