HUUM HIVE Flow LS PkgWood Burning Sauna Stove Package w Firebox Extension, 9. 8kW The HUUM HIVE Flow LS Sauna Stove Package with a Firebox Extension comes complete with the HIVE Flow LS Sauna Stove and Sauna Stones. Its innovative design ensures that 75% of the heat from the firewood directly heats your sauna rather than escaping through the chimney. It stands out as one of the most efficient and environmentally sustainable heaters for sauna rooms from 282 to 635 cubic