Proper Sauna Rocks: The Real Reason You Need Them

Whether wood-burning or electric, sauna heaters are used with sauna rocks, but why? And how to ensure you’re choosing the best sauna stones to get the most out of your sauna?

In this article I’m going to answer these questions while replacing old sauna rocks with new ones in my own sauna. I’ll also introduce the types of stones that are most suitable for sauna use.

Since I’ve run into questionable information around the topic of buying sauna stones vs. picking them from the wild, I’ll discuss that too and reveal the real reason you might want to opt for proper sauna stones.

Finally, I’ll share a discount code for everyone interested in real sauna stones mined in the United States, a local alternative to sauna rocks that are normally imported from Finland.

What Are Sauna Stones for?

There are three important things to understand about the purpose of sauna stones and how to use them:

1. Every sauna heater, electric or wood-burning, requires sauna rocks. They’re never optional. The heater heats the rocks that you then pour water on to produce steam (löyly), which is the whole point of sauna bathing.

2. The best sauna rocks have great heat retention capacity and thermal conductivity, meaning they stay hot for long and release that heat, ensuring proper löyly.

3. You’re always meant to throw water on the hot sauna stones to create löyly. Dry sauna is not a thing!

Whenever you see online sources claiming sauna rocks are a nice addition to your sauna heater but not a must, that is FALSE information and you should ditch that “resource” immediately. Traditional sauna heaters are never meant to be heated without stones, which the instruction manuals also make very clear.

And if you happen to witness something even worse, such as an electric sauna heater left empty while there are a few rocks placed on top of the radiating heating elements, you should facepalm and ditch that source even faster:

What Kind of Rocks Can You Use in a Sauna?

Can you use lava rocks for a sauna? Yes, lava rocks, also known as igneous rocks or volcanic rocks that are formed by the cooling and hardening of magma, are exactly what the most known sauna heater manufacturers recommend.

They retain heat effectively, giving you even heat, and are durable, which ensures they withstand high temperatures without cracking or breaking. The low porosity of igneous rocks reduces cracking as water can’t get trapped inside, which could make the stone pop or explode when it gets hot.

Can sauna rocks popping ever be normal? Yes, it’s normal for used and aged sauna rocks that split in half, and is safe as it happens inside the heater.

Stones that are not suitable for sauna use can explode more violently, though. In a thorough sauna stone durability test, red granite, meant only for decorative use on top of other sauna rocks, burst completely.

A legitimate alternative for igneous rocks are ceramic sauna stones made of clay (more about them later).

What Are the Best Rocks for a Sauna?

The following types of stones are the approved, most popular, and most widely available options.

✅ Olivine diabase (sometimes also called olivine gabbro): This rock is durable and has the best price-quality ratio & safety profile. It’s also more easy to find on the US market than other commercial options.

✅ Peridotite: Deemed the best sauna rocks in durability, but they have gotten increasingly rare because they were linked to asbestos before the 2000s; the commercial peridotite you find today for saunas is tested for asbestos and therefore safe, but availability is poor and prices high.

✅ Olivine (troctolite): This less common option is heavier than its cousin olivine diabase, which correlates with better heat retention.

✅ Vulcanite: This blackish option is more durable than olivine diabase but less than olivine; it’s also more expensive and less widely available than olivine diabase. I tested one batch for years and found it did really well and looked amazing with silver (for many, the appearance of sauna stones is also a consideration):

The four types above are the only sauna stones the most known sauna brand Harvia allows in their sauna heaters. Another well-known brand, Huum, also seems to abide by these recommendations, with olivine diabase as their favorite.

Other possible options with some (local) variation:

🔶 Basalt: A viable option in the US (some of the best sauna tent packages come with basalt sauna rocks), but basalt isn’t identical in all parts of the world; in Iceland, for example, basalt is more vesicular, which means it contains lots of small holes, making it porous and therefore far from ideal for sauna use.

🔶 Granite: Claimed to be great in some sources written in English, but was the first rock type to crumble into bits and pieces in a Finnish durability test in 2019. It’s no wonder Harvia, for instance, allows granite sauna rocks to be used only as decoration on top of other stones as they’re not allowed to touch the heating elements.

🔶 Soapstone: Not durable enough to be used throughout the heater, but can be used on top of other rocks for decorative purposes; in correct use, soapstone can easily outlive many other rocks.

Ceramic sauna stones (like the brand Kerkes) are the only artificial rocks in this listing, made of clay, resulting in mostly glass that develops when clay is processed in extremely high temperatures, almost melting the glass to form a hard, durable “rock.”

People debate about ceramic sauna rocks the most, some loving their durability and lifespan that’s easily at least twice as long as with traditional sauna rocks, meaning less maintenance as the stones don’t have to be replaced nearly as often.

Some, on the contrary, don’t like them in home use, think they’re ugly, and that their heat retention capacity is poorer than that of ordinary stones. They’re also not allowed to be used in all sauna heaters. They’re much more common in commercially used saunas due to savings in maintenance costs.

What Sizes, Shapes & Colors Should You Choose?

Getting the right-sized sauna stones is equally important as durability and safety since too large stones obviously won’t fit (in electric heaters) while too small stones stack up too tightly, not allowing air to flow, which would compromise proper heater function.

Electric sauna heaters require smaller stones, 2–4 in (5–10 cm), than wood-burning ones, 4–6 in (10–15 cm), as the rocks have to fit between the heating elements.

Regarding the shapes, they affect what kind of steam (löyly) you get: rounded and smooth stones bring softer steam as the water has no rugged surfaces to absorb to.

With rounded sauna stones, there’s also less size variation, and they’re easier to stack.

Angular stones, on the other hand, are often as asymmetrical as possible, which gives them a large water surface area, resulting in more intense-feeling heat and steam.

Most sauna rocks are either gray, blackish or white. The white ones are usually decorative and only recommended to be used on top of other sauna stones. Granite can be reddish while ceramic sauna stones are brownish.

Remember that you can mix different stones for löyly and/or aesthetic reasons: you can have angular stones but place rounded stones only on top of them; this will soften the steam. The rounded stones on top can also be red granite or white, for instance, if you prefer such a look.

Can You Source Sauna Rocks from Nature for Free or Is It Wiser to Buy Proper Sauna Stones?

Most sauna stones sold in the US, be they from any brand, are mined in Finland and then shipped to the US. That’s why they can be expensive and not widely available. Because of this, some people wonder whether they can source stones themselves directly from nature and use them in their sauna.

You potentially can.

Saunas have existed for thousands of years; people obviously picked and used rocks directly from the outdoors as there weren’t any sauna companies to buy stones from. Some people even tested the rocks by the fire before using them in the sauna, just to see how they behaved and handled the heat.

So yes, if you own land or have permission to pick dozens or even hundreds of pounds of rocks needed for your sauna heater, that is something you could do. If it sounds interesting to you, there’s one realistic expectation you should have, though: commercial sauna stones have much longer lifespan.

When Finnish sauna competitors tested several kinds of sauna stones in 2011, including commercial sauna rocks and natural stones they picked themselves by a lake, they loved the colors, shapes and smell of the self-picked stones, but the durability wasn’t great: during a 3-month test period, some of the rocks split in half in an electric heater while a wood-burning sauna stove destroyed even more rocks!

That actually makes a lot of sense for a reason I haven’t seen any sauna sources mention: proper sauna rocks (i.e., mined stones) are excavated from deep within the bedrock, making them “fresh” because they come from unexposed rock layers that have never faced weathering. That means their structural integrity is high.

Riverbed rocks, on the other hand, are victims of natural water erosion. Them being attrited and waterworn means that they can have micro-fractures and that they’re not “new” in the sense mined stones are.

If going for a DIY sauna stone setup:

🔸 choose sturdy rocks with no cracks; the ones darker and more uniform in color are more durable than lighter and/or patchy stones

🔸 since self-picked stones are less durable than commercial ones, be prepared to replace them much more often for best heater functionality

🔸 asbestos is no joke or marketing ploy; asbestos is found in mafic rocks that would otherwise be excellent for sauna heater use; it has been confirmed (Forsman, 1997) that when a rock contains asbestos and is used in a sauna-like setting (water thrown onto it in a hot environment), it releases asbestos particles into the air

I’ve already given you many reasons to use proper sauna stones instead of self-sourced ones, but let’s conclude this section with the #1 reason you might want to opt for officially approved sauna stones: they are a must if you don’t want to void the warranty!

Many sauna heaters come with a 2-year warranty. If you’ve bought a sauna heater, and the warranty is still valid, I’d stay away from any stones the manufacturer doesn’t approve. No brand loyalty is required as long as the type of stone is correct. You can use Narvi’s olivine diabase stones in a Harvia heater, for instance, without voiding the warranty.

Sauna Stones for Sale: Where to Find Them?

If you’ve wondered where to buy sauna rocks, already tried to buy them online, or searched for sauna stones near you, you may have noticed the following:

• most hardware stores don’t sell them
• Amazon sells them (for expensive prices)
• Home Depot sells them online
• Lowe’s doesn’t sell them at all
• many online stores don’t let you buy sauna stones alone but require you pair them with a sauna heater; that can be fine initially, but a heater can last for 10–15 years (or longer), while stones need replacing every few years

Shipping heavy sauna stones can also be costly, making cheerful promises of “only $120 away from free shipping!” feel less encouraging than probably intended.

That’s why I partnered with trusted and much loved North Shore Sauna that sells proper sauna stones mined in Minnesota & offers free shipping for orders over $100. If you need six or more boxes, you get $50 off with the code SAUNAIS50.

North Shore’s sauna rocks are olivine gabbro “sourced from a 1.1-billion-year-old vein of Northern Minnesota bedrock” and available in the two industry-standard sizes (2–4 in & 4–6 in), checking every box for every requirement that we discussed above.

Having this local option is a welcome alternative to importing sauna rocks from Finland. Olivine gabbro (under that specific name) is among the approved types of sauna stones in Finland too where it’s nowadays less commercially available than olivine diabase.

Frequently Asked Questions (FAQ)

1. How long do sauna rocks last and how often should I change them?

This depends on how often you go to sauna and what type of rocks you use.

Many manufacturers say you should at least check the stones once a year and restack them, replacing the ones that are seemingly aged and/or that crack during testing.

Not all stones have to be replaced at once every time you replace rocks. Some of them can easily last for at least 2–3 years in regular use. After that the weakening and crumbling will speed up.

2. How to know when to replace an old sauna rock?

Fully broken or slightly cracked stones are the easiest to spot and should be replaced.

Discoloration is another useful clue, indicating the rock has endured a lot.

Many stones pass the visual tests above, but have still weakened so much that they can break in your hands, even when not using any force.

For all rocks that seem and feel fine, you can do a final test just to be sure: grab two rocks and hit them together. If either of them cracks, it should be replaced with a new one.

3. Is it OK to pour water over sauna rocks?

Not only OK, but a must! Both for enjoyment and for best heater functionality.

Pouring water over sauna rocks isn’t just a recommendation, but some sauna heater instruction manuals call it a necessity.

Why do you put water on sauna stones? Doing this produces löyly (steam), which is what sauna bathing is all about.

4. How long do sauna rocks take to heat up?

This depends on the size of your sauna and your sauna heater type. Heaters with more rocks take longer to heat but then they also stay hot for longer.

A very small sauna can be ready to use in 25 minutes while my 3-person sauna, for example, requires at least 45 minutes during colder seasons. During summer, it heats faster.

Nowadays there are sauna heaters the rocks of which are heated at all times (thanks to standby heat function), so with a heater like Harvia Forte, it only takes 5–15 minutes for you to get proper löyly.

In heat storing sauna heaters (found in smoke saunas and some other home saunas as well), it takes several hours or even the whole day (!) to heat up the sauna stones.

Final Thoughts

When people wonder what stones are good for a sauna, what actually matters far more is the frequency you replace them with new ones.

Replacing sauna rocks often enough is not only the best way of improving your sauna experience, but it can also easily make it feel like you bought a new sauna heater! The difference new stones make truly is that big.

While proper sauna rocks are always superior, safer, and have a longer lifespan than stones picked in the wild, even the self-sourced ones can work if you replace them with “new” (in reality, waterworn) ones possibly twice or even three times a year.

In practice, though, that is what extremely few sauna owners do. Most people are too lazy to replace sauna stones. I don’t even want to think of all the people I know who haven’t done anything to the rocks in their sauna heaters for 5+, in some cases even for 10+ years!

And it shows because it’s natural for sauna rocks to crumble over time and lose their functions as they start turning into dust. That process takes far less than 10 years.

Some people only replace the stones on top since that’s the easiest thing to do, and you also see the state of those rocks instantly. It’s not enough, however, to just keep doing that year after year.

At some point, you’re going to do your sauna heater a much-appreciated favor when you restack and even replace all the stones.