Rounded Olivine Diabase Sauna Stones, 5–10 cm (15 kg box)

Most HUUM heaters take 5–10 cm stones, including the DROP, HIVE, HIVE Mini and CORE, and the HIVE Wood and HIVE Flow stoves. These rounded olivine diabase stones match that spec. Their smooth shape lets water run down into the pile before it evaporates, which HUUM says gives softer steam, and the dense stone holds heat well. Load larger stones low and smaller ones on top, keep the stack loose so air can circulate, and rinse off the dust first. Plan the whole load at once, because bigger heaters take many boxes.