STEEL heater was developed with small home saunas and space saving in mind. Therefore it has a very slim design and significantly reduced safety distances from the walls. The small safety distances are achieved by optimizing the structure and placement of the internal air tunnel. However, the compactness does not come at the expense of efficiency. The internal air tunnel placed in the center of the heater provides effective airflow, speeds up the heating process by 25% and prolongs the lifespan of the heating elements.