Sauna stove stones have two main functions: Firstly, they act as a "thermal battery" by storing heat and radiating a stable, even temperature throughout the sauna room. Secondly, when water is poured over them, they produce "löyly" steam, which humidifies the dry air and significantly increases the perceived temperature. This enhances perspiration and provides a more enjoyable sauna experience.

Only specially manufactured, volcanic stones should be used in a sauna stove. Ordinary river or garden stones can contain trapped moisture, which expands rapidly at high temperatures, causing them to explode and potentially leading to serious injury or stove damage. Furthermore, some natural stones may release harmful gases when heated.

Stones should be arranged loosely to allow air to flow freely from the bottom of the stove, through the heating elements, and out the top. Larger stones should be placed at the bottom, and smaller ones on top, without pressing against the heating elements. Incorrect or tightly packed arrangement obstructs airflow, causing the stove to overheat, operate inefficiently, and leading to premature failure of the heating elements.

Sauna stones are consumables that crack and crumble over time due to constant thermal shock. For home saunas, they should be inspected annually, with crumbled stones replaced and the remaining ones rearranged. In commercial saunas, due to higher usage, it is crucial to replace them entirely every six months to ensure the stove's efficiency and longevity.