So I think I understand the general theory of the rocks on the sauna stove. The stove heats them up. They radiate heat. They also help in boiling water when you toss it on top of them. Getting the type of heat you want is an art that takes tweaking and testing. The sizes of the rocks also affect the heat. Big rocks take longer to heat up and longer to cool down. Smaller rocks are the opposite.
You can also purchase sauna rocks online (and I’m guessing in stores too). I saw prices of about $60 for 50 lbs of rock. Yes ladies and gentlemen, we’re talking about paying $60 for rock. That’s about 5 cases of beer. About 60 beer bottles. About… oh you get the idea. I started with robbing my yard of landscaping rock. I got about five 5-7 inch rocks, fired the stove and got the hot room up to about 190F. After a bit more scavenging, I felt sad about it and went to the big box store and bought a $10 bag of “natural” stone with each rock being about 3 inches wide. Oddly enough, the rock was imported from India—I guess we lack rock here. I emptied the whole bag and sorted the rocks around the stove. Firing the stove this time, I could hardly get it to reach 180 after about 3 hours of burning. I will have to remove some rock to see if things improve. Also, one thing I’ve noticed is that the landscaping rock came covered in some sort or rubbery substance. It took about an hour of burning off and pouring water on the rocks to get it to bubble away. Really hurt the eyes :) One note of advice, you need solid rock like granite NOT limestone. Limestone rocks can explode when heated!
Now I think a big part of a sauna, besides a wood burning stove, is the smell. That’s where scented oils come in. Mixing a few drops with a cup of water and pouring on the rocks, not only hugs you in humid heat, it also clears your sinuses by hitting you in the nose. It’s a hug and punch! Having just bought a few different scents, I really wanted to try all of them. Since my sauna bucket is still in the mail and I didn’t have water right next to me in the hot room, I figured I put straight scented oil drops on the hot rocks to get the smell to release. Well you know what happens to oil with heat? It lights up to a nice flame. Lesson here? DON’T PUT SCENTED OIL ON HOT STONES!