Sauna rock use
You need to use the tight type and size of rocks to use for a sauna. They must be constantly cleaned to keep their effectiveness.
You need to use rocks like granite, basalt, hornblende or Peridotite because these rocks can withstand constant and repeated heating and cooling.
You need to use large rocks and pack them loosely in a circle shape. Fill the heater on top of the rocks with smaller stones. They will retain heat efficiently.
The top rocks must be cleaned once a year and replaced after using them 2 years. Lower to base rocks can be used 5-6 years.