All of our heaters have:

Stainless steel elements for long life.
Large rock capacity for heat storage.
Direct rock contact with heating elements-necessary to filter the harsh heat radiating from the 1400° F elements, to eliminate the electo magnetic field for safe and therapeutic bathing: (the bather feels only pleasant, soft heat) and to produce the best steam when water is poured over them.
Free airflow for faster heating.
Maximum strength and durability from pressed metal design.

Finlandia and Harvia Sauna heaters have 3-wall construction for cooler surface temperature and greater safety.