Hot rocks . . .

Which rocks are best?

There is more to know about the stones in your sauna than you may realise . . .

A sauna works by heating stones in an electric or wood-fired oven storing the temperature for a long time which in turn continuously heats the air in the sauna. The main purpose of the stones in the heater is to retain enough energy to vaporise the water thrown on top of the stones. The stones must not be too fragile, emit heat too quickly or degrade and release lung corroding vapours.

The stones we use are classified as Peridotite, a dense, coarse-grained igneous rock consisting mostly of the minerals olivine and pyroxene. Peridotite contains less than 45% silica, is high in magnesium from the olivine and has about an equal amount of iron. It is an ideal rock for sauna use.

Rocks to avoid include those that contain asbestos and sulphur. Sedimentary and metamorphic rocks are also unsuitable. These rock types may release harmful vapours, unpleasant odours and degrade quickly requiring frequent replacement. Rocks containing a high quartz or iron content should also be avoided as they may explode when water is poured over the hot rock.

SAWO quarry Peridotite sauna stones in Finland and ship them worldwide specifically for sauna use. Evenly sized for placement and of the highest natural quality, these stones are our recommendation for optimum results.

How often should rocks be replaced?

Due to the continual heating and cooling, Peridotite sauna stones will deteriorate over time and like the heater itself they should be monitored on a regular basis.

We recommend that the sauna stones be removed from the heater at least annually or every 500 hours (whichever occurs first) with the small ones discarded and any fine particle dust removed.

Important: The heater must always be isolated from the power supply prior to undertaking any work on it, including replacing the sauna stones.

Once the stone compartment has been cleaned, the stones should then be replaced loosely around the heating elements so that they do not block air circulation through the heater. The stones should cover the elements to avoid water being poured directly onto the components and to ensure correct heater operation.

If required, an additional 20kg box of sauna stones can be purchased from us here.