We at saunatimes get questions about sauna rocks. Until a geologist or thermal heat inspector checks in, we’re going to wing a few points for review. Whether a wood burning sauna stove or an electric sauna stove, sauna rocks play an important role.
What size sauna rocks? Softball to golf ball. This size range works well. Why? Different size sauna rocks hold heat (thermal mass) differently and release steam (loyly) differently from water being tossed on hot sauna rocks. A nice hot wood burning sauna stove or electric sauna stove will heat your sauna rocks, then as water is tossed on the sauna rocks, the water turns to steam, and that process will temporarily cool your sauna rocks. Softball size sauna rocks hold more heat and will maintain thermal mass better. The golf ball size sauna rocks react quicker to the water, turning it to vapor but at the expense of thermal mass. You want different size sauna rocks.
What kind of sauna rocks? Some swear by igneous rocks, or volcanic rocks. Though lava rocks have a high heat capacity, we find that they don’t hold thermal mass. Why is thermal mass so important? We find that an integral part of the sauna experience is the thermal heat, or dense heat, that is only created by heating mass. (think heavy water heated radiators vs. tinny electric baseboard). There is a theory that sauna manufacturers sell and promote volcanic rocks for sauna stoves because they are lighter weight so more reasonably priced to ship. (What did you get for Christmas? “A box of rocks!”).
We are a big fan of granite rocks. Specifically, rounded aged granite rocks from the icy shores of Lake Superior. Rocks without cracks or crevices. There is a stigma and fear that sauna rocks can explode. Sure, if you’re using rocks that allow for water to get in cracks, they will surely explode! If you’re worked up about that, you can read about Hydrofraction. Bottom line: use non porous granite rocks on top of your sauna stove.
Why sauna rocks? Consider that savusaunas, the earliest form of saunas, are “simply a room containing a pile of rocks, but without a chimney.” The rocks are heated by fire, with lots of wood and for a long time. Then, the fire goes out and all that heat is contained within the rocks. This same principle, heated rocks, is what differentiates a sauna from a fake. (here’s where we throw infrared light bulb closets under the bus).
Consider building your collection of sauna rocks as a journey, not a destination. Hiking, walking along the beach, snooping around your neighbors backyard are all times to have your granite sauna rock radar detector going. Oh, and how about how much water to toss on your sauna rocks?