Sauna Stones 101: Materials, Sizing & Stacking for Perfect Löyly
Why Stones Matter
Stones are the heat battery of a traditional sauna. The right rock stores energy, the right stack breathes, and together they create the soft, rolling steam known as löyly. For a quick refresher on the physics, see our post The Physics of Löyly. For a Finnish design overview that includes stone selection basics, see Saunologia – Essentials, Part 4.
Best Stone Materials (and What to Avoid)
- Olivine diabase (peridotite/dolerite): The Finnish standard for durability, heat capacity, and thermal shock resistance. See examples/specs via Harvia dealers (Harvia Olivine Diabase).
- Basalt / gabbro: Dense igneous stones that hold heat well; quality varies by source. Vet for sharp fracture & porosity.
- Avoid river rocks & soft, laminated stones: Hidden moisture layers can pop or spall; stick to heater-rated stones from reputable suppliers (Saunologia).
What Size Stones Do I Need?
Manufacturers publish sizing ranges to balance surface area (steam) with airflow (even heating):
- Wall-mounted/electric: typically 5–10 cm diameter; do not overpack. Examples: Narvi NM manual (5–10 cm guidance).
- Floor units / big baskets: often 50–80 mm+ with larger pieces at the base for flow (Helo CAVA/ROXX manual).
- Mixed grading: larger stones low + smaller stones higher improves both breathing and steam (supplier example: Finnmark sizing notes).
How to Stack Stones (So Your Heater Can Breathe)
- Rinse first: remove dust before loading (Helo/Harvia both recommend rinsing: Helo manual, Harvia stacking guide).
- Loosely, not tightly: leave channels between stones; do not wedge against elements or frame (Narvi manual).
- Orientation: think “arrowheads pointing up” so air can rise through gaps (Saunologia – identifying/stacking tips).
- Layer strategy: larger, more rugged stones on the bottom and perimeter; smaller pieces fill but don’t choke the basket (Finnmark).
Maintenance: When to Rinse, Restack, Replace
- Quick check each season: remove fractured or glazed stones; turn and restack for airflow (Harvia stone care).
- Full service interval: stones are a consumable; plan replacement based on use (Saunologia’s 6-step change guide: How to replace stones).
- Steam test: if water runs out the bottom or hisses without vapor, stones may be too cool or stacked too tightly (Helo FAQ).
See our broader care guide: Essential Sauna Maintenance Tips.
Common Mistakes (Easy to Fix)
- Overpacking the basket: chokes airflow, overheats elements, slows warm-up (Narvi).
- Using decorative stones: only install heater-rated stones; some ceramics are for specific commercial models (Helo stones page).
- Skipping the rinse: dust burns and smells on first heat; always rinse first (Helo manual).
Quick Selector: Pick & Stack Like a Pro
| Heater Type | Stone Size | Stacking Notes |
|---|---|---|
| Wall-mounted electric | 5–10 cm | Rinse; loose stack; keep off elements (Harvia guide) |
| Floor-standing / big basket | 50–80 mm+ | Large bottom/perimeter; smaller infill (Helo manual) |
| Wood or pellet heaters | Manufacturer range | Favor dense igneous stones; restack seasonally (Saunologia) |
Related Reading
- How Sauna Stove Design Shapes the Experience
- Why We’re Building Tova for 110 V
- Saunologia: Stove & Stone Selection
- Harvia: Stone Care Guide
Bottom Line
Choose dense, heater-rated stones; size them to your unit; stack for airflow, not just fill. Keep the basket breathing and the stones fresh, and your löyly will stay soft, powerful, and pure.