Sauna stones
The short answer
Use stones made for sauna heaters, usually olivine diabase, in the size and weight your heater's manual gives. Harvia says a sauna used about twice a week needs new stones once a year. A 20 kg box costs about €45 to €51 in Ireland, and most heaters need one to six boxes.
On this page
Which stones
Heater stones have to cope with being heated and splashed with water thousands of times. Sellers mostly use olivine diabase quarried in Finland. Harvia also sells black vulcanite, and some heaters need round stones. Harvia warns against stones from the beach or garden: many crack under heat, and some contain harmful substances.
- Size: usually 5 to 10 cm or 10 to 15 cm. Some heaters use both, with larger stones at the bottom.
- Type: whatever your heater's manual specifies. If in doubt, ask the heater's seller before buying.
How many you need
Heater manuals give the weight of stones in kilograms. Examples from Finnmark's list:
| Heater | Stones | 20 kg boxes |
|---|---|---|
| Narvi Slim (electric) | 30 kg | 2 |
| Luosto (wood-burning) | 35 kg | 2 |
| Narvi NC 20 (wood-burning) | 60 kg | 3 |
| Aito 24 (wood-burning) | 80 kg | 4 |
| Narvi Softy (electric) | 120 kg | 6 |
Too many stones block the airflow and overheat the elements. Too few give weak, spiky steam.
When to replace them
- Once a year if you use the sauna about twice a week, according to Harvia. More often with heavier use.
- When they crumble or discolour. Harvia suggests tapping stones together to test them; weak ones crumble.
- When they're smaller than your fist, Finnmark's rule of thumb.
- If the sauna is slow to heat, or you find grit under the heater.
Stacking them
- Switch off and let the heater cool completely.
- Take all the stones out, and check the elements. Discolouration or limescale is worth asking the seller about.
- Rinse the stones and let them dry. Throw out any that crumble.
- Stack loosely, largest at the bottom, so air can flow between them. Don't wedge stones between the elements or pile them high over the top.
Harvia publishes stacking videos for wall-mounted, pillar and professional heaters. Follow the one for your model.
What they cost
| Seller | Stones | Price |
|---|---|---|
| Timbertrove | Harvia olivine diabase, 20 kg | €45 |
| Finnmark Sauna (Irish site) | Narvi olivine diabase, about 20 kg | €50.95 |
Prices as listed in October 2026. Timbertrove showed its box as sold out. Delivery is extra on heavy boxes, so check before ordering.
Common questions
How often should you change sauna stones?
Harvia says that if the sauna is used about twice a week, the stones should be changed once a year. Finnmark suggests every one to two years, or once stones have worn smaller than your closed fist. Check them at least once a year either way.
Can I use any stones in a sauna?
No. Use stones sold for sauna heaters, usually olivine diabase or similar. Harvia warns that many natural stones are unsafe: they can contain harmful substances or crack when heated and cooled.
How many sauna stones do I need?
Use exactly the weight your heater's manual gives. It varies from about 20 kg for small heaters to over 100 kg for large ones. Too many blocks the airflow; too few gives weaker steam.
Where can I buy sauna stones in Ireland?
Sauna sellers and online shops sell them in boxes of about 20 kg. We found Harvia stones listed at €45 a box at Timbertrove and Finnmark olivine diabase at €50.95 a box (October 2026).
Should you wash new sauna stones?
Yes. Rinse them to remove dust before stacking, and let them dry. Harvia also suggests washing stones you reuse when you restack the heater.
Sources
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