Can you handle the heat and humidity of a Finnish sauna? Vaisala sensors can

What’s the hottest place on earth that you’d be willing to go for fun? For many people the answer would be “a sauna.” In Finland, the sauna is an integral part of life, and if you’ve never experienced it, you may have wondered what such heat really feels like. As part of recent research into ambient air conditions inside saunas, Vaisala’s Indigo80 handheld and its sensors were put to the test.

A favorite Finnish tradition

A sauna is a small room or building designed to create dry or extremely humid heat. Different regions experience the sauna in different ways, but there’s one country in the world that takes sauna to the next level: Finland. There are over three million saunas in the country, which is more than the number of private cars.

In Finland, saunas can be found everywhere, from summer cottages and national parks to hotels and prisons. A Finnish sauna is typically heated to between 60 °C and 100 °C (140 °F – 212 °F). Water is then thrown on the sauna stones, raising the temperature and creating steam and humidity. The steam and high heat relaxes muscles and lowers blood pressure.

Humans can withstand these conditions because we sweat, but what about sensor technology? If we compare these conditions to industrial manufacturing, it’s safe to say that the conditions inside a sauna are harsh – and a good test of how robust a sensor is.

A tradition worthy of study

Sauna is such a serious business in Finland that the ideal conditions are a subject of intense debate – and even academic research. According to Professor Tuomo Tuomola, writing in Sauna magazine in 1969, the recommended wet-bulb temperature in a Finnish sauna is 45–53 °C.

The recommended temperature and humidity conditions of a Finnish sauna were defined with the help of a graph showing the suitable humidity of sauna air (40 gH2O/kgair – 70 gH2O/kgair) and dividing the sauna conditions – based on dry and wet -bulb temperature – into gentle, moderate, or hard bathing.

Continuing this interest in measuring sauna conditions, in 2023 Saunalogia, a Finnish organization that promotes sauna culture, carried out a study that aimed to document current sauna conditions and compare them to recommended conditions from previous decades. The idea was to be able to inform visitors about what they can expect from sauna conditions today.

As well as heat and humidity, the study also looked at other parameters like carbon dioxide and particulate matter – both hot topics in today’s air quality discussions.

The Vaisala Indigo80 takes a sauna

Vaisala was chosen as the research partner for the study, and eight saunas were tested in cooperation with Vaisala's product development unit.  

The measurements were made using a Vaisala Indigo80 – a compact, handheld indicator and data logger that can measure multiple parameters – such as humidity, temperature, dew point, and carbon dioxide. For this study, a Vaisala carbon dioxide sensor (CO₂ Probe GMP252) and an air humidity and temperature sensor (Relative Humidity and Temperature Probe HMP7) were connected to the recorder.

The temperature and humidity conditions were measured in the saunas at a single point 30 cm from the ceiling, usually close to the traditional wall-mounted thermometer. The sensors were attached to a floor stand. The concentration of carbon dioxide and particulate matter were measured near the floor, at a lower temperature.

The measurements were taken in each sauna for 15 to 26 minutes. The minimum time was chosen based on the temperature sensor, which is the slowest to adapt to the sauna environment. If there were no other users in the sauna, the researchers threw one scoop of water on the sauna stove at least twice during each measuring session to create steam. Temperatures in the saunas varied between 74 ℃ and 120 ℃, and average wet-bulb temperatures between 35 ℃ and 46 ℃.

Sauna conditions vary greatly – and that’s no bad thing

So, it was hot and humid in the saunas, as expected. The results show that the humidity of the tested saunas clearly exceeds the limit of the “hard bathing” area defined by the Sauna Society in the 1960s, and all the saunas except one achieved the 40 gH2O/kgair “recommended humidity” zone.

The study also demonstrated that conditions in saunas can vary from day to day, especially in wood-fired and gravity-ventilation saunas. This variation in conditions is a positive rather than a negative, because it allows the sauna-goer to control their own exposure to heat – and enjoy the sauna exactly as they want to.

The results showed that the conditions in the saunas were good and showed no cause for concern, based on wet-bulb temperature and carbon dioxide measurements. The study also demonstrated that Vaisala Indigo sensors were able to handle the harsh conditions and still deliver accurate results.

Want to sweat the details and see what can Vaisala sensors do for your demanding industrial process? Contact us to discuss more.