Harvia Sauna Heater Stones are made from dense olivine diabase quarried in Western Finland. These traditional dark stones are built to tolerate repeated high temperatures without breaking, which helps protect heating elements and fireboxes. Each stone measures 2–4 in (5–10 cm), with angular, split-face surfaces that stack securely in the heater basket while still allowing air to circulate.
The rough surfaces warm quickly and produce full, smooth steam when water is thrown on the stones. They are suitable for electric heaters and as a top layer on wood-burning heaters.