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How do you know it’s time to replace sauna stones?

Recognizing sauna rocks which have gone old is not hard and every sauna owner should know how. Check out four tips for figuring out when it is the time to have new stones for your sauna heater to avoid damaging your heater or decreasing your sauna pleasure!

Regular inspection and replacement of sauna stones is the most frequently needed sauna maintenance procedure (well, after cleaning). Sauna stones degrade over time and unless they are serviced, their aging will negatively influence the operation of the heater, cause additional thermal load for it, waste energy, reduce sauna air quality, and create a mess.

Changing and inspecting sauna stones is normal maintenance item for both electric and wood-burning heaters. How often it needs to be done fully depends on the amount of sauna use.

Based on my research into the longevity and durability of the stones, I recommend that If your sauna is being used once a week for two hours, commercially produced sauna stones should last at least couple of years. I suggest they would be best inspected annually.

At the other extreme, commercial saunas heated every day will require maintenance at least quarterly. The type of stone will affect the expected lifespan, but this pales in comparison to the effect created by the amount of use.

One of the methods I have used to study sauna stones is to heat them to 700 degrees Celsius (1300 F) and drop into ice cold water. Proper stone will survive this easily.

Inspecting the stones

Always wait until the heater is fully cooled down (And turned off, timers disabled, preferably totally disconnected from the mains) before doing any work around. When inspecting the stones, you take care to avoid cuts from the heater or broken stones. Wearing gloves is a good precaution.  A headlamp may come very handy with heater models that are “closed” from the sides.

In the inspection, the majority of the stones should be removed from the heater for the assessment of stone and heater integrity.

In an electric heater, pay attention to possible structural damage to heating elements (bends, dents, and other damage) as well the body. In wood-burning stoves, check out how the firebox looks like, is it badly misshapen or are any welding seams cracking . Sometimes you may need a hammer to release stones jammed due to thermal expansion. The stone may be okay, but you should remove if you can to release tension and make room for the proper re-installation of the stones.

Usually the heater gets messy because of broken stones

Four signs that the stone should be changed

Inspect the stones both visually and by gently banging the stones against one another. Watch out for the following signs that can tell you that the stone should be discarded:

  • Stone is chipped or broken into pieces.
  • Stones have changed their color from dark to gray, white, green, black, or anything out of the original. Usually this happens for the topmost stones as a consequence of making steam as mineral residues builds up.
  • Stones breaks or chips when it hits another stone. Start gently, repeat the test with more force.
  • The stone feels fragile or hollow when it this another stone.

Watch the tips on a YouTube video:

All stones that are falling apart should be immediately replaced. In Finland, I usually recommend just replacing all of the stones that don’t look like they are good as new because their price is negligible in comparison to the effort of just inspecting. Elsewhere in the world, the stones may be in a shorter supply and prices higher so I don’t make the same recommendation, just get rid of the broken and strange coloured ones.

Strong discolouration, a green tint, due to unknown properties of water.

After you’re done re-install the  old, still usable stones or the new ones. Saunologia currently does not have a specific guide for stone replacement in English but check out the videos below for visual cues on how to replace the stones. The first video is for electric heaters, the second for wood-burning ones. Pay attention to the orientation of the stones, they are laid like arrowheads pointing upwards, not sideways. This maintains good airflow between them.

Typical very end-of-life signs for small natural stones

For disposal, I recommend placing the old stones back to the nature at your backyard. They are not hazardous and shouldn’t end up in the landfill.

Acknowledgement: this article has been produced as a part of collaboration between Saunologia and our partner Sauna-Eurox sauna stones manufacturer.


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Saunologi ja saunan suunnittelun tutkimusmatkalainen. Johtava nykyaikainen suomalaisen saunan asiantuntija ja Suomen Saunaseuran Löylyn henki -palkittu 2021. Työkseni suunnittelen parempia digitaalisia palveluita. Minulla on pitkä historia tieteellisestä tutkimuksesta ja opetan satunnaisesti Aalto-yliopistossa.

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