Throwing water to the stove in the sauna

A common sauna discussion is the one about the effect of throwing water on the sauna stove, and how it affects the temperature in the sauna: whether it just feels hotter due to the humidity, or if the temperature actually rises?

I read an excellent blog article about the topic, from the Saunologia blog (link).

To begin with, there are multiple effects at play:

• Water on the stove will rapidly transfer heat from the stove to the air, in the form of steam and hot, humid air. This will raise the temperature.

• Longer term, the overall heat input from the stove does not change, the same energy is still put into the system through the wood burning in the stove.

• Humans feel increased heat, even beyond the increased temperature due to (1) hot steam condensing on colder skin surface, and (2) our natural cooling system (sweating) not being able to cope as efficiently with the increased humidity.

In short, there is an actual temperature increase, but it is perhaps not as big as one might think, typically in the order of few degrees, however, that and the interaction with human skin will make the sauna feel hotter. And can of course affect the skin negatively, if done in excessive amounts.

The linked blog article explains the physics of heat transfer from the stove, and how it affects the temperature and humidity in the sauna. There's an excellent Mollier diagram showing the impact of throwing water at a 80 or 120 degree sauna, and how it slightly increases the temperature and significantly increases humidity. The diagram is by Unto Hakkarainen:

Pictures from my cottage trip where one of these discussions happened :-)

For more sauna and swimming stories, check out planetswimmer.com and saunablogger.cool websites! And of course the Planetcaver, and Planetskier blogs for other stories in Blogspot and TGR! The photos and text (c) 2025 by Jari Arkko. All rights reserved.