Sauna Stones

Sauna stones are natural or volcanic rocks placed on the sauna heater’s heating element, where they store heat and release steam (löyly) when water is poured over them. A suitable stone must withstand repeated sharp temperature shocks without cracking or breaking apart, so dense, homogeneous rocks such as olivine, peridotite, or vulcanite are preferred. The size and shape of the stones affect airflow around the heating elements and the evenness of heat storage. Over time, stones become coated with mineral deposits from the water and wear mechanically, which reduces their ability to store heat efficiently. The quality and type of stones directly affect the intensity and character of the steam in the cabin.

Advantages of quality sauna stones

• High resistance to temperature shocks: A correctly chosen stone withstands repeated cycles of high heat and cold water without cracking.
• Even heat storage: A homogeneous, dense stone structure allows stable steam release when water is poured on.
• Free airflow around the heating elements: Correct stone size and placement ensures efficient heat transfer from the heater into the cabin.
• Long service life with periodic replacement: Regular inspection and replacement of worn stones keeps the heater’s output at its original level.

Which stones for a sauna: a comparison of rock types

The question of which stones for a sauna to choose has a short answer: a rock that stands up to repeated thermal shock. Three types are used in practice, and they differ in density and in the character of the steam.

How to stack the stones in the heater

• Do not pack them tight. Air has to flow freely between the stones, otherwise the heating elements overheat and their service life is shortened.
• Larger pieces at the bottom, smaller ones on top. The bottom layer holds the arrangement together, the top one increases the surface area for evaporation.
• The stones do not lean on the elements. They should sit around them, not rest their full weight on them.
• Rinse them before first use. Dust from quarrying and transport would otherwise smell when the heater is first fired up.
• Restack them once a year. During the check, cracked pieces are discarded and the rest is stacked again.

Related terms: Sauna heater, Integrated sauna heater, Incoloy® 800/825, Ventilation.