Extra Small (3-5 cm) Sauna Heater Stones 33 lbs of 1" - 2" (3-5 cm) of rounded olivine sauna stones. We highly recommend using rounded stones in HUUM heaters to complement the design and have milder steam. Rounded shape to complement heater design Durable with high-heat capacity Stones range from 1" to 2" (3-5 cm) To ensure optimal performance and safety, each sauna heater requires a specific number and size of stones. CLIFF Mini- 4kW - 132 lbs (60 kg), 1-2" (3-5 cm) - 4 x 33 lbs CLIFF- 6kW, 9kW, 11kW - 165 lbs (75 kg), 1-2" (3-5 cm) - 5 x 33 lbs STEEL Mini- 3.5kW - 133 lbs (60 kg), 1-2" (3-5 cm) - 4 x 33 lbs STEEL- 6kW, 9kW, 10.5kW - 331 lbs (150 kg), 1-2" (3-5 cm) - 10 x 33 lbs