Harvia Sauna Heater Stones (4-6 in, 44 lbs) deliver robust heat storage and an authentic sauna feel for both electric and wood-burning heaters. Cut from dense olivine diabase sourced in Western Finland, these larger 4–6 inch (10–15 cm) pieces withstand repeated firing without crumbling, helping protect elements and fireboxes. Their angular, split-face surfaces stack securely while leaving channels for air to move freely through the heater cavity, supporting efficient warming and responsive steam. When you pour water over the stones, they release a rich, soft löyly that fills the room with steady, enveloping heat rather than sharp bursts. The natural dark gray tone complements traditional log saunas as well as modern metal-clad units, making the 44 lb box a dependable choice for building a stable rock bed with strong heat retention and consistent steam production.