Heat, infrared and the body's response
Convective versus radiant heating
Convective heating warms you through hot air or steam touching your skin. Radiant heating warms you through infrared radiation crossing the gap directly. A Finnish sauna is mostly convective, a far infrared sauna mostly radiant, and a steam sauna adds condensation on top of both.
Also called convection heating, hot air versus infrared
The distinction decides how hot the room has to be for you to feel hot.
Convection. Air is heated at a source, moves, and gives up heat where it touches you. Air is a poor conductor and holds little heat for its volume, so convective systems have to run the air very hot — 70 to 100 °C in a Finnish sauna — to move a useful amount of energy into a body.
Radiation. An emitter sends infrared across the space and your skin absorbs it. The air in between is largely bypassed, so a radiant sauna can feel strongly warm with cooler air. This is the appeal of far infrared heating.
Condensation, the third mechanism, and the one people forget. In a steam sauna, water vapour condenses on skin that is cooler than the vapour, and condensing water releases a large amount of latent heat as it does so — far more than the same mass of hot air could carry. This is why steam at 45 °C feels much hotter than dry air at 45 °C, and why a modest temperature inside the sauna is not a mild exposure. Our first-session guidance of 30 to 37 °C should be read with that in mind.
Our ozone steam saunas use all three: convection and condensation from the steam generator, radiation from the far infrared emitters, and conduction from the seat.
Why it matters here
It explains why 37 °C in a steam sauna feels far more demanding than 37 °C in a room, and why a steam sauna's temperature cannot be compared directly against the numbers quoted for a Finnish sauna.