Humidity and Temperature Terms Used in Sauna Specs

What the three terms mean

When you open a sauna manual or a spec sheet, three numbers usually stand out: the relative humidity, the set point, and the maximum temperature. Each answers a different question. Relative humidity tells you how much water vapor is in the air relative to how much it could hold at that temperature. The set point is the target temperature you enter on the control panel. The maximum temperature is the upper limit the unit is designed to reach under normal conditions.

All three appear in different places in the listing, and confusing them leads to mismatched expectations. A sauna that lists a high maximum temperature might still feel harsh if you run it below the set point you actually prefer. A steam generator, on the other hand, is rated by steam output, not by relative humidity, because the room is sealed and the air becomes saturated. This article explains each term and gives you practical questions to ask before you buy.

Relative humidity in sauna specs

Relative humidity (RH) is the ratio of water vapor in the air to the maximum amount of water vapor the air can hold at that temperature, expressed as a percentage. Warm air holds more moisture than cool air, so a reading of 20 percent at 170 degrees Fahrenheit represents far more actual water vapor than 20 percent at 70 degrees Fahrenheit. In sauna listings, the humidity percentage matters less than the type of heat, because the experience depends on whether you add water to the rocks or not. The difference between dry sauna vs wet sauna comes down to this choice.

Cleveland Clinic notes that traditional saunas are typically heated between 150 and 195 degrees Fahrenheit (65.55 to 90.55 degrees Celsius) and most have low humidity, about less than 20 percent. Infrared saunas are different: they warm the body directly rather than the air, so humidity is not a setting you adjust. Finnleo's FAQ states that for infrared saunas, humidity is ambient and no water should be added to the sauna. The practical takeaway is that a traditional sauna gives you control over humidity by pouring water on the stones, while an infrared cabin does not. That burst of steam is known as loyly.

When you see a relative humidity number on a spec sheet for a traditional sauna, it usually refers to the moisture level during normal use without extra water on the stones. Some manual will also state a maximum humidity for the room, often tied to the wood or the electrical components. If you plan to use the sauna as a wet sauna, check that the listing differentiates between dry use and wet use. The same heater can produce very different humidity depending on how much water you pour.

• A traditional sauna runs dry unless you toss water on the stones; one ladle is typically enough for a noticeable burst of steam.
• Infrared saunas should not have water added to the interior, because the emitters are not designed for moisture exposure.
• Steam showers are the opposite: the whole point is high humidity, and the generator produces steam until the room is saturated.

Set point: the number you dial in

The set point is the temperature you enter on the sauna controller. It is the target the heater works toward, not a fixed output. A manual might say the control range is 80 to 195 degrees Fahrenheit, but that is just the range you can select. The set point you choose determines how long the heater runs and how hot the room gets. If you set it low, the heater cycles off when the sensor near the ceiling reaches that value.

In a traditional sauna, the control typically reads air temperature in the room. The heater keeps running until the sensor near the ceiling reaches the set point, then cycles on and off to hold it there. Finnleo's FAQ recommends a comfortable range of 150 to 175 degrees Fahrenheit for traditional saunas and 120 to 130 degrees Fahrenheit for infrared models. That is much lower than the maximum most units can hit, which is why you should plan on using the set point, not the maximum, as your daily target. For a list of models with clear set point ranges, see our best traditional sauna gear and best infrared sauna gear roundups.

For steam showers, the set point works differently. The generator heats water until it boils, and steam is produced as long as the unit is on. The control on a steam system, like the iSteam3 from MrSteam, lets you set time, temperature, and other features, but the room temperature is a consequence of steam production, not regulated by a thermostat alone. The manual will tell you the recommended set point range, and it is usually tied to the room finish, because tile, glass, and acrylic hold heat differently.

Maximum temperature: the ceiling, not the goal

The maximum temperature listed in a sauna spec is the highest the unit can reach under normal operating conditions. It is a safety and design limit, not a comfort recommendation. Most sauna bathers prefer temperatures well below that ceiling. Cleveland Clinic states that traditional saunas are typically heated between 150 and 195 degrees Fahrenheit, with most below 20 percent humidity. The upper 195 degrees Fahrenheit figure is the top of the typical range, not a target.

Infrared saunas list a lower maximum temperature, typically between 110 and 135 degrees Fahrenheit according to Cleveland Clinic. Finnleo's FAQ gives a similar figure of 120 to 130 degrees Fahrenheit for infrared models. Because infrared warms the body directly, the air temperature stays lower than in a traditional sauna, and the set point on the control reflects that. If you see an infrared listing that claims a maximum temperature above 140 degrees Fahrenheit, check whether it is an air temperature reading or a panel surface temperature.

For steam generators, maximum temperature is rarely the relevant number. The generator produces steam at the boiling point, and the room temperature depends on the steam output and the room insulation. MrSteam's design guide notes that steam rooms should be sized with the generator to match the cubic footage and finish material. The maximum meaningful spec is the steam output in pounds per hour, not the air temperature. If you are comparing a sauna and a steam generator, remember that the temperature ranges are not comparable: a sauna is dry heat that feels very hot in a dry way, while a steam room feels hot and humid. For a deeper comparison, read our article on steam room vs sauna vs steam shower.

Reading the humidity section of a spec sheet

Spec sheets for traditional saunas sometimes list a relative humidity range, such as "10 to 30 percent." That range usually refers to the dry-use humidity when the heater is running without additional water, and the wet-use humidity when you pour water on the stones. The exact number depends on the room size, ventilation, and how long you keep the door closed. A manual might also specify a maximum safe humidity to protect the wood and the electrical components.

For infrared saunas, the spec sheet often does not list humidity at all, because the experience is designed to be dry. If a listing for an infrared cabin does state a humidity number, it is likely the ambient humidity of the room, not a controlled value. You should not add water to an infrared sauna, as Finnleo notes: "For infrared saunas, humidity is ambient and no water should be added." Water on the emitters or the floor could damage the unit and create a slip hazard.

Steam showers never list relative humidity as a spec, because the steam generator fills the enclosure with vapor until the room reaches saturation. The relevant spec is the generator output in pounds of steam per hour, and the control's set point for time and temperature. A good steam system will also include an auto-flush feature to clean the tank after each use, as described in MrSteam's FAQ about the AutoFlush option. If a steam listing claims a specific relative humidity number, treat it as a marketing figure, not a controlled measurement.

How to use these terms when you buy

When comparing saunas, ignore the maximum temperature and focus on the set point range and the humidity type. Ask yourself whether you want a dry heat that you can occasionally moisten by pouring water on stones, or a wet heat that saturates the room. If you want the traditional Finnish experience with loyly (the steam burst from water on hot stones), a traditional sauna with a low humidity baseline is the right choice. If you want moderate temperatures and no humidity management, an infrared cabin is simpler.

Read the manual to find the range of the controller, not just the maximum. Some heaters have a high maximum but a small set point range, which means you cannot dial in the low temperatures you might prefer. Also check whether the humidity spec refers to dry use or wet use. Many traditional sauna manuals list a maximum safe humidity for the room structure, and exceeding it could warp the wood or strain the ventilation.

For a steam shower project, the humidity term that matters is the steam output of the generator, not a percentage. The generator must match the cubic footage of the enclosure and the finish material, as noted in the sizing guides from MrSteam, or the room will not heat up evenly. If you are choosing between a sauna and a steam unit, the temperature ranges are not the deciding factor: the decision is whether you want dry heat or humid heat. Cleveland Clinic notes that there is no clear indication that one is better than another, so the choice comes down to preference.

Practical questions to ask before buying

Before you settle on a model, find the manual online and look for the control range, the humidity rating, and the maximum temperature. Then ask these questions. What is the lowest set point? If you like a mild session, a unit that only starts at 140 degrees Fahrenheit may be too hot. What is the humidity ceiling? For a traditional sauna, that tells you how aggressively you can use water. Is the sensor for the set point placed at the ceiling or bench level? A ceiling sensor will read higher than the bench where you sit, which can make the heater cycle differently.

The answers affect your experience more than the maximum temperature numbers. A sauna that lists 195 degrees Fahrenheit as the max can still be perfectly comfortable at 160 degrees Fahrenheit, which is a common preference according to Finnleo's FAQ. If you are looking at a steam generator, ask about the control functions: does it have a timer, a temperature setting, and an auto-flush? The MrSteam iSteam3 and similar controls offer time and temperature management, and an auto-flush protects the tank from scale buildup, which MrSteam's FAQ recommends.

Use the links below to compare models by the terms described here. The buying guides break down the set point ranges, humidity type, and maximum temperatures for each category, so you can filter for the experience you want. Start with a guide that matches your preferred heat type, whether that is traditional, infrared, or steam.

• Look at the controller range, not the maximum; most sessions run well below the limit.
• Check the humidity type: dry for infrared, adjustable for traditional, and saturated for steam.
• Find the sensor location in the manual; ceiling-mounted sensors read hotter than the bench you sit on.

What to pick for your use

Questions

What does relative humidity mean in a sauna spec?

Relative humidity is the percentage of water vapor in the air compared to the maximum the air could hold at that temperature. In a traditional sauna, the spec often lists under 20 percent for dry use, and the humidity rises when you pour water on the stones. Infrared saunas do not control humidity, and steam showers are meant to reach saturation.

What is the set point on a sauna control?

The set point is the target temperature you enter on the controller. The heater runs until the sensor reaches that value, then cycles to hold it. It is separate from the maximum temperature. Most people set the temperature between 150 and 175 degrees Fahrenheit in a traditional sauna and between 120 and 130 degrees Fahrenheit in an infrared unit.

Is the maximum temperature a safe number to compare?

Not really. The maximum is a design limit, not a comfort recommendation. You will rarely use it. Compare the set point range and the humidity type instead. A unit with a 195 degrees Fahrenheit maximum is still used comfortably at lower set points.

Do I need a separate hygrometer to check humidity?

You can use a hygrometer to see the humidity in a traditional sauna, and it is useful for confirming the dry baseline. But the manual's spec is what matters for safety. If you stay within the recommended water volume, the humidity should stay in range. For infrared and steam, a hygrometer is not necessary.

Why does my infrared sauna listing not mention humidity?

Because humidity is not controlled in infrared units. The emitters warm your body directly, and the air temperature stays lower. Adding water is not recommended, as it could damage the emitters. The term to look for is the temperature range, not humidity.