Sauna Stones: Which Type, How Many Your Heater Needs, and How to Load Them
The stones are the cheapest part of a sauna heater and the one people think about last. They are also what gives you the heat and the steam, and how you choose and load them decides how well the heater works and how long it lasts.
This guide covers the three questions that matter: which stones, how many, and how to put them in. Every figure comes from the heater manufacturers' own charts and manuals.
What the stones actually do
They store the heat. The heater warms the stones, and the stones hold that heat and give it back to the room, softly and evenly.
They make the steam. When you ladle water on hot stones, it turns into steam. That burst of moist heat is what Finns call löyly, and it only works if there is enough hot stone for the water to reach.
They protect the heater. In an electric heater, the stones surround the heating elements. Harvia explains that air must be able to move between the hot stones and the elements: good air circulation in the stone space is what makes the elements last. Its manuals also warn that pouring water over exposed elements can damage the heater, so the stones must cover them completely.
Split-face or rounded?
Split-face stones are broken, angular stones. Harvia calls them the right choice for electric heaters and wood-burning stoves: they store a lot of heat, water evaporates quickly from their wide, rough faces, and their angles keep them from packing tightly, which leaves room for the air to flow.
Rounded stones look like river stones. HUUM, Saunum and Narvi stones are rounded, and so is one of the two Cozy Heat stones. Their makers describe a milder, softer steam, because the water runs down between them and reaches the deeper layers before it evaporates.
The two can be combined. Harvia recommends angular stones in the bottom layers and rounded ones on top. Its updated stone instructions are precise: if the elements of an electric heater touch the stones, rounded stones may only go in the outer layers, where they do not touch the elements.
Decorative stones are a top layer, nothing more. Harvia's white AC4000 stones go over the regular stones, never instead of them, with one box at most per heater. HUUM advises against decorative stones in its DROP heater, because they do not store enough heat and break easily. Harvia's warranty does not cover damage caused by decorative stones or by stones it does not recommend.
What they are made of
Harvia lists four suitable materials: peridotite, olivine diabase, olivine and vulcanite. The stones we sell are olivine diabase or olivine, apart from one vulcanite and the white decorative stones.
- Olivine diabase is the classic sauna stone: dense, it absorbs and stores heat well and tolerates repeated heating and cooling.
- Vulcanite is a fine-grained dark grey volcanic rock that shines black when wet. Harvia's AC3040 is the vulcanite option.
- Heat-treated olivine diabase, like the Harvia AC3050, has been exposed to about 1,000 °C. Harvia makes it for intensive use, such as busy public saunas.
Do not use stones from your garden. Cozy Heat's manual explains why: stones found in nature may contain harmful substances such as iron pyrite. Use stones sold for sauna heaters.
Size: follow the heater, not the box
Sauna stones come in three sizes: 1 to 2 inches, 2 to 4 inches, and 4 to 6 inches. The right size is the one your heater's manual asks for. Most electric heaters take 2 to 4 inch stones. Some HUUM heaters, such as the CLIFF and STEEL, take 1 to 2 inch stones, and so does the SaunaLife Titan propane heater. Harvia's wood-burning stoves take 4 to 6 inch stones.
How many stones does your heater need?
This is the figure people get wrong most often, and the range is wide: from 29 lbs for a compact heater to more than 300 lbs for some large stoves.
| Heater | Minimum stones | Boxes | Stone to use |
|---|---|---|---|
| Harvia Vega and Vega Compact | 29 lbs | 1 x 44 lbs | Harvia AC3000 |
| Harvia KIP and The Wall | 44 lbs | 1 x 44 lbs | Harvia AC3000 |
| Harvia Spirit | 110 lbs | 4 x 33 lbs | Harvia R-991 |
| Harvia Virta and Virta Combi, 6 to 9 kW | 110 lbs | 3 x 44 lbs | Harvia AC3020 |
| Harvia Cilindro, 6 to 9 kW | 200 lbs | 5 x 44 lbs | Harvia AC3000 |
| Harvia M3 and M3 SL wood stoves | 66 lbs | 2 x 44 lbs | Harvia AC3020 |
| Harvia Pro 20, 26 and 36 wood stoves | 88, 110 and 132 lbs | 2, 3 and 3 x 44 lbs | Harvia AC3020 |
| HUUM CORE | 66 lbs | 2 x 33 lbs | HUUM Stones 2-4in |
| HUUM DROP | 122 lbs | 4 x 33 lbs | HUUM Stones 2-4in |
| HUUM HIVE Mini | 330 lbs | 10 x 33 lbs | HUUM Stones 2-4in |
| HUUM HIVE Wood 13 / HIVE Wood 17 | 199 / 287 lbs | 6 / 9 x 33 lbs | HUUM Stones 2-4in |
| Saunum Air 7 | 110 lbs | 4 x 33 lbs | Saunum Heater Stones |
| Cozy Heat wood stoves | 175 to 350 lbs, by model and power | 44 lb boxes | Cozy Heat stones |
| SaunaLife Titan SL1 (propane) | 44 lbs | 1 to 2 inch stones | see the heater page |
From the Harvia and HUUM stone charts and the manufacturers' product data, November 2026. Always check the manual of your exact model.
Two things to notice. First, the minimum is a minimum: a stone space that is too sparsely filled is dangerous, and HUUM's DROP manual states it plainly: it causes a fire hazard. Second, natural stones vary in shape, so Harvia and Cozy Heat suggest an extra box, to be able to choose the stones that fit best.
How to load them
- Wash them first. Harvia, HUUM, Saunum and Cozy Heat all ask you to rinse the dust off the stones before loading them.
- Place them one by one. HUUM asks you not to pour or throw stones into the heater. Wear gloves.
- Big stones at the bottom. HUUM recommends the larger stones at the bottom and sides, with smaller ones to hold them in place.
- Loose, not packed. The stones must not be forced between the elements, and must leave room for air to circulate. Stones packed too tightly restrict the air flow and reduce the heating capacity.
- Hide the elements. When you are done, the heating elements, or the stove body on a wood stove, should not be visible between the stones.
Saunum and some HUUM models have their own loading rules, so read the stone section of your manual before you start. HUUM recommends that a specialist lays the stones in its DROP heater.
Looking after them
Stones break down with the constant heating and cooling. The manufacturers give the same advice in slightly different words:
- Harvia and Cozy Heat: rearrange the stones at least once a year, or more often if the sauna is used a lot. Remove the broken pieces from the bottom of the heater and replace the crumbled stones with new ones.
- HUUM, for the DROP: a visual check after 100 hours of use or at least once a year, rearranging and replacing cracked stones after 200 hours, and a full set of new stones after 400 hours.
Settled or crumbled stones leave gaps, and gaps let the elements overheat. Harvia notes that keeping the stone space in order is the user's responsibility for the warranty to stay valid. Use only clean tap water on the stones.
The stones we sell
| Stones | Material and shape | Size | Box | Price |
|---|---|---|---|---|
| Harvia AC3000 | olivine diabase, split-face | 2-4 in | 44 lbs | $65.56 |
| Harvia AC3020 | olivine diabase, split-face | 4-6 in | 44 lbs | $68.89 |
| Harvia AC3040 | vulcanite, split-face | 2-4 in | 44 lbs | $180 |
| Harvia AC3050 | heat-treated olivine diabase, split-face | 2-4 in | 44 lbs | $270 |
| Harvia R-991 | olivine diabase, rounded | 2-4 in | 33 lbs | $113.33 |
| Harvia AC4000 | white decorative, top layer only | 2-4 in | 22 lbs | $217.78 |
| HUUM Stones 2-4in | olivine, rounded | 2-4 in | 33 lbs | $180 |
| HUUM Stones 1-2in | olivine, rounded | 1-2 in | 33 lbs | $165 |
| Saunum Heater Stones | olivine diabase, rounded | 2-4 in | 33 lbs | $155 |
| Cozy Heat Traditional | olivine diabase, split-face | 4-6 in | 44 lbs | $65 |
| Cozy Heat Premium Rounded | olivine diabase, rounded | 4-6 in | 44 lbs | $120 |
| Narvi Round Stones | olivine diabase, rounded | 4-6 in | 44 lbs | $165 |
Prices as of November 2026. The current price is always on each product page.
Some stones are only sold together with a heater of the same brand. Each product page says whether that is the case. All our stones are in our sauna stones collection.
Common questions
How many boxes of sauna stones do I need?
Divide the minimum weight your heater needs by the weight of one box, and round up. A Harvia Cilindro that needs 200 lbs takes five 44 lb boxes. The table above gives the figure for the heaters we sell.
Can I use rocks from my garden or a landscaping store?
No. Natural stones that are not sold for sauna heaters may contain harmful substances such as iron pyrite, and Harvia's and HUUM's warranties do not cover damage caused by unsuitable stones.
Can I mix brands of stones?
Use the stones your heater's manufacturer specifies. Saunum, for example, asks for Saunum stones in its Air heaters.
How often should I replace sauna stones?
Rearrange them at least once a year and replace the crumbled ones. For the HUUM DROP, HUUM recommends a full set of new stones after 400 hours of use.
Do package heaters include the stones?
Some do. Our heater packages list the stones they include, such as the Harvia Vega BC35 package with a 44 lb box, or the HUUM DROP packages with 132 lbs of stones. A heater sold alone needs its stones ordered separately.
Where to go next
Still choosing the heater itself? Our guide What Size Sauna Heater Do I Need? matches the power to your room, and How Much Does a Home Sauna Cost? puts the heater and its stones into the full budget. You can also browse all our sauna heaters.
And if you are not sure which stones fit your heater, send us its model name. We will tell you which stones and how many boxes it needs.
