Sauna Heater Rocks – A Complete Guide for Choosing the Best Sauna Rocks

Sauna heater rocks play the most essential part in providing you with the perfect sauna experience. Since the origin of the sauna, these special kinds of rocks have been used to heat the room and maintain the warm temperature of the room throughout the session. This is due to the fact that these rocks have certain absorption properties which allow them to absorb the heat and then slowly release it – just like a battery absorbs energy and releases it.

All rocks, however, are not the same. Some absorb heat faster and better than others while others explode when exposed to high temperatures. Therefore, not every rock is ideal for sauna heaters. In this article, we will be going over everything you need to know about choosing the perfect sauna heater rocks.

Sauna Heater Rocks

What type of rocks is ideal for Sauna Heater?

Rocks can be divided into three broad categories – sedimentary, metamorphic, and ingenious. Sedimentary and metamorphic rocks are not feasible for sauna heaters. Their dense, porous nature prevents them from efficiently absorbing and retaining the heat. In addition to this, the pores may also contain moisture which can cause them to explode or crack under high temperatures.

Instead, sauna heaters should use ingenious rocks. These rocks are also called volcanic rocks and have a very high thermal mass which makes them ideal for absorbing and retaining heat for long periods of time. Granite rocks, a type of ingenious rock, have proven to be perfect for a good sauna experience.

In addition to this, rocks from lakes with smooth surfaces are also a good alternative for ingenious rocks. As their surfaces are smooth, they are less likely to develop cracks and explode.


What type of shapes and sizes of rocks is ideal for Sauna Heater?

At present, sauna rocks are usually about the size of your palm or a medium-sized potato. However, in the past, large sauna rocks were used in traditional saunas as they absorb more heat and retain it for longer periods of time. Today, with the development of electric and woodburning heaters, we do not require our heaters to retain heat for very long and thus, large rocks are not needed.

The size of the sauna rocks typically ranges from 5 cm to 15 cm in diameter, depending on the size of your heater and the stove of the heater. The larger the stove of your heater, the larger rocks are used.

As for shapes, all shapes of rocks are ideal. It is recommended that you use a variety of different shapes so that they all easily fit in the space provided, leaving no empty space.

Moreover, there has been a debate among many sauna users regarding whether round-shaped rocks produce better steam or rocks with pointed edges. Harvia and Finlandia, two of the most renowned sauna heater brands, believe that split-faced rocks with pointed edges are superior. However, in our opinion, they both produce more or less the same result. While round-shaped rocks produce more soft steam, rocks with pointed edges produce a stronger wave of steam as a result of more surface area being exposed. It all depends on your preference and which rocks provide you with better aesthetics.


How to improve the performance of Sauna Heater Rocks?

One of the most common ways of improving the performance of Sauna Rocks is to splash cold water on them. This will result in a strong blast of hot steam and produce a blissful sensation known as Loyly in Finnish. Remember not to throw large amounts of cold water altogether on the rocks. This will cool the rocks and produce less Loyly. The best way is to drizzle 3-5 ounces of water during a single sauna session. In addition to this, start with small amounts of water and gradually increase to allow the stones to properly heat up.

Apart from this, the arrangement of the rocks inside the stove also affects the overall performance of the sauna. In the case of a Wood-burning heater, place larger rocks at the bottom because they will offer a larger surface area to the fire directly below them. This will result in the production of more steam. On the other hand, in the case of electric heaters, arrange the rocks between the heating rods.

However, in both cases, arrange the rocks loosely so that there is ample room for air circulation but this does not mean that you leave empty spaces in which you could fit more rocks. Leaving empty space adversely affects the performance of the sauna and the quality of the steam. Also, make sure that some rocks are leftover before you start the session as during the session rocks sometimes contract due to the heat and sink in. This will create room for more rocks which you can add later.

Do not rush filling up the stove! Enjoy filling the rocks like a puzzle!


How often should Sauna Rocks be replaced?

A common question among many sauna users is how often the sauna rocks should be replaced. This depends on how often you use your sauna. Typically, it is recommended not to replace sauna rocks until they form cracks, which takes several years. However, in the case of public saunas, rocks are heated every day and thus, they crumble very quickly and need to be replaced quite often.

Nevertheless, it is recommended that you check the rocks every six months for any cracks or if any part has peeled off and needs replacement. Apart from this, regularly change the arrangement of the rocks. Rotate the positions of the rocks in the bottom layer as they are the ones most vulnerable to heat and likely to form cracks.


Steps to ensure that rocks are safe for use in a Sauna Heater:

When choosing the perfect sauna rocks, there is a number of steps you should follow to ensure that the rocks are safe and reliable.

Firstly, drop them on the floor with force and then check to confirm no part chipped off. If they do not stay unchipped, then they are not strong and reliable for your sauna heater.

Secondly, scratch the rocks’ surfaces using any sharp object or a nail and ensure nothing peels off. Lastly, throw the rocks into a fire pit for a few minutes, and then after taking them out, immediately put them in cold water. If the rocks are not solid enough, they will crumble due to the sudden change in temperature from extremely hot to extremely cold.



Discovering the finest sauna heater rocks is one of the most crucial steps in achieving the ultimate sauna experience of your life. Ingenious/Volcanic rocks of all shapes and sizes are best suited for sauna heaters. In addition to this, a proper arrangement of rocks and a good splash of water can greatly improve the quality of steam being produced by the rocks. However, it is important to ensure that the rocks you choose are safe and reliable and will not crumble under harsh temperatures as this can lead to accidents such as the explosion of rocks.

We are sure that by following the guidelines of this article you will be able to choose the most perfect sauna heater rocks which will immensely enhance your sauna experience.