What Are Sauna Stones? Everything You Need to Know!

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For the best possible sauna experience, look to your sauna stones. They retain and properly emit the heat from the stove, and they release steam when you pour water over them. You can’t just throw in any type of rock and expect great results. This guide will tell you everything you need to know about sauna stones. 

Sauna stones smooth out the temperature in a sauna and provide a surface to splash water on to create steam. You can purchase them online or at home/garden stores (sometimes sold as decorative rocks), or you can find your own. They should be roughly fist-sized, and you’ll need 10-20 of them.

Sauna stones are integral to your sauna and your experience in it. The room houses the heater. The heater warms the stones. The stones heat the room consistently and intensely. The entire system heats you, allowing you to reap the many benefits of the sauna. Let’s dive into the details around how sauna stones pull this off, and why they’re so important to your sauna experience. 

What Are Sauna Stones For?

Sauna stones stacked on a wooden surface

Sauna stones like the Scandia All Natural Sauna Rocks set (on Amazon) aren’t just there to make your sauna look more earthy and inviting. Unless you’re using an infrared sauna, which does not use rocks, they’re the key to the entire experience. Sauna rocks serve two key functions: 1) absorbing and retaining heat, and 2) producing steam.

While a sauna does have a stove powered by gas, electricity, or burning wood, a stove alone won’t provide that heavy, consistent, long-lasting, sweat-inducing heat. Think of a small room heated by a furnace, radiator, or portable heater. It gets warm, maybe even unpleasantly so, but it lacks the heavy, evenly distributed heat of a sauna. That room heater also won’t produce a burst of steam. If you threw water on an electric heater in your office, you’d ruin the heater and have a mess to clean up. 

The same is true for a sauna heater. It needs something to help it create the right type of heat. Sauna stones are placed in and around the heat source. They take in the heat slowly and retain it for hours, emitting energy at a slow, constant rate so that your sauna is hot enough to make you sweat and the warmth is consistent. 

Sauna stones create that wonderful sauna environment. And it must be stones—not pebbles, gravel, sand, or dirt, because part of the reason they work is the thermal mass they hold after being heated all the way through. Unlike these other substances, sauna stones are thermally conductive and they have a lot of dense bulk to them, which means they both absorb and release heat more smoothly than something with more surface area.

For readers who are a bit more scientifically minded, what we’re discussing here is the ratio of surface area to mass, which is why the same stone material broken up into gravel wouldn’t give you the same results: there’s a lot more surface area compared to larger stones. 

Stones are also responsible for another important part of the sauna experience: steam! While saunas are different from steam rooms (see our guide comparing the two), a traditional sauna still uses some steam. Once the stones are hot, water can be added to them in small bursts to generate steam and humidity in the space. This encourages more sweating because it causes your body to perceive a temperature higher than what the room actually is. Sauna stones offer a safe way to sweat without the risk of heat exhaustion. Not just any rock will do the trick. Only certain stones can serve as sauna rocks.

What Makes a Good Sauna Stone?

Coasts SSBAG Replacement Sauna Heater Rocks Stones 40 Pounds

If you’re building your own sauna, it may be tempting to focus on the other details and just throw some rocks into the heater as your final step. Now that you know how essential and fundamental sauna stones are to your complete experience, though, you might be reconsidering your approach to sauna stones! Even if you aren’t building your own but are replacing your existing stones, it’s equally important to know what makes a good sauna rock. 

Correct rock type is essential to both the quality of your experience and your safety. A good sauna rock heats efficiently (neither too quickly nor too slowly), is able to retain the heat, offers a smooth surface to ladle water onto, and doesn’t explode when it gets too hot (yikes!). 

As a quick geology refresher, there are different types of rock, including igneous, sedimentary, and metamorphic. Sauna rocks must be igneous. Sedimentary rocks (like sandstone, shale, or limestone) are formed from the accumulation of minerals on the Earth’s surface, while metamorphic rocks (such as slate, marble, or quartzite) are formed when hot fluids are exposed to high heat or pressure.

These aren’t suitable for sauna use because they’re either too soft, have flaws, or contain moisture. They’ll be ineffective at best and dangerous at worst. Igneous rocks are rocks formed from cooled molten lava. They include rocks like olivine, granite, peridotite, vulcanite, basalt, gabro, rhyolite, pumice, and obsidian.

Opinions differ as to which igneous rock is the best sauna stone. Many favor olivine because it is so dense. There is complete agreement that pumice and obsidian make terrible sauna rocks. Pumice (also known as the only rock that floats) is too light and porous, while obsidian is too smooth. When considering igneous rock for your sauna, it’s helpful to have some criteria so you know what to look for. 

Qualities to Look for in a Good Sauna Stone

  • Dark color. Rocks that are too light in color reflect heat rather than absorb it. 
  • Medium size. For proper heating efficiency and retention, the majority of stones should be between 3-15 centimeters (1 to 6 inches), about the size of a baseball or adult fist.
  • Rough texture. Rough, uneven surfaces give water something to cling to. If water just slips over smooth stones, you won’t get the desired burst of steam.
  • Flawless. This means free of cracks or crevices. If water seeps down into a sone, the heat will cause hydrofracture—breakage or even an explosion.

Can You Find Your Own Sauna Stones in Nature?

You may want to buy bundles of replacement sauna stones like the Coasts Replacement Sauna Heater Stones (on Amazon), but you can also go foraging for your own! As long as you follow the above criteria for good sauna stones the end results will be the same. Buying prepackaged stones or searching for your own is simply a matter of personal preference. 

If you are gathering your own collection of personally chosen rocks, there are many places to look. You can search your own property, especially if you have a lot of land. Landscape businesses are a great source because they sell a variety of rocks. They often have piles of rocks they don’t use and will sell them for a low price for anyone willing to sort through them and carry them away. Avoid buying rocks classified as decorative if they’ve been highly polished or painted. 

You can also search out in nature, but be aware that there are restrictions. Many national, state, and local parks don’t allow people to remove objects, including rocks. Check with the relevant park department for their unique regulations. Be considerate, too, in searching on someone else’s private property and ask permission before taking their rocks.

How Should Sauna Stones Be Placed?

Sauna stones are housed in a basket or box above or around the stove. Follow these sauna stone placement guidelines for high-quality heat and steam as well as prolonged stove life:

  • Rinse your rocks before placing them in your basket to remove debris or factory chemicals.
  • Sort stones by size. Pack primarily with medium-sized stones. Use small stones to fill spaces including in and around the heating element. Large stones, if any, should be placed close to the heating element rather than at the edges of the heater.
  • Use the entire space of the container, but take care to avoid putting pressure on the heating elements.
  • Leave just enough space between stones to allow for sufficient airflow, but avoid big gaps in order to achieve maximum heat conduction. 
  • Dark stones absorb more heat than light ones. If you prefer the look of light stones, you can pack the inside of the basket with dark rocks and use light-colored rocks near the exterior where they’re visible. 

Store-bought stones are easy to use because they tend to be uniform in size. Some people prefer the rustic, authentic look achieved by using stones of different sizes and shapes. If this is your preference, you might enjoy hunting for your own sauna rocks. 

How To Maintain Your Sauna Stones

We have a separate article on how to properly clean and maintain your sauna, but here we’ll briefly review maintenance of just the sauna rock component. It’s important to inspect your stones approximately every six months (more or less frequently depending on how often you use your sauna). Heat causes rocks to degrade over time. Replace any cracked or otherwise damaged rocks immediately. 

Sauna stones are convenient to purchase and come in prepackaged bundles. You can buy proper sauna rocks in a variety of local and online locations, including sauna specialty stores, large hardware franchises like Lowes, Home Depot, Walmart, and even Amazon.

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