When to replace sauna stones

Stones wear out. Nobody can say exactly when for your heater, but they tell you if you look. Pieces on the floor, cracks, crumbling, or a heater that's slower than it used to be.

Signs a stone is done

• Bits under the heater. Harvia says stones disintegrate slowly because of the big swings in temperature, and you can spot it when stone pieces turn up on the floor of the sauna room¹.
• Cracks and crumbling. Harvia says to discard any stones that crumble or are discoloured². HUUM lists cracked or broken stones and excessive stone dust as reasons to inspect³.
• Dull sound. Hit two stones together. Harvia says if they crack and sound shallow, it's time to swap the disintegrated ones for new¹.
• Feels lighter. HUUM says to replace stones that are eroded or have become remarkably lighter⁴.
• Slow heating. HUUM lists longer heat-up times among the signs to inspect³.

Why it matters

Broken stones don't stay put. Harvia says they can shift into smaller cavities in the heater body and pack too tightly². That restricts airflow, which can cause the elements to overheat and the sauna to heat up slower².

How often, according to the makers

There's no single number. The makers tie it to use.

HUUM adds that a sauna used four times per week can add up to approximately 200 hours in a year³. Your heater's hours depend on how you use it, so go by your own manual if it gives a schedule.

A yearly check, step by step

Harvia's guide gives a simple routine²:

1. Turn the heater off and let it cool.
2. Remove all the stones.
3. Look over the heater's elements while the stones are out.
4. Discard any stones that crumble or are discoloured.
5. Tap the rest together to check their strength.

Harvia also says to recycle old stones following the sorting rules in your area, or use them in a garden².

Before the good stones go back in, wash them and let them dry². Also take out any stone debris from the bottom of the heater¹.

Heavy use

Harvia sells heat-treated stones for places with intensive use, such as public saunas, and says the treatment gives them a longer service life¹. The same maker says to rearrange stones even more often if the sauna is in frequent use¹.

Replace some, or all?

HUUM says the most convenient solution is to replace all the stones at the same time⁴. Harvia's guidance is to discard the ones that crumble or are discoloured². Either works with the maker who recommends it.

Start with the heater off and cool². Then follow the loading page to put the stones back, and the cleaning page for the ones you're keeping.