06.11.2026
Why are there stones in sauna? 10 more FAQs about sauna stones
Why are there stones in sauna heaters, and what difference do they really make? Sauna stones absorb and retain heat, help distribute it throughout the sauna, and create leil – the wave of hot, humid air produced when water is poured over hot rocks.
The stone type, stone load, size, shape, and placement all affect how a sauna heater performs. Choosing the right stones is therefore an important part of getting the best performance and leil from the heater. Explore HUUM sauna stones to find the recommended stone types and sizes for HUUM heaters.
Most sauna owners know that stones create leil. Fewer realize that their size, condition, and placement can also influence heating time, airflow, and heater performance.
So how many sauna stones do you need? Why are round stones recommended? How should sauna stones be stacked, and when should they be replaced?
This guide answers 11 common questions about sauna stones.
Sauna stones at a glance
Sauna stones at a glance come down to a few simple rules:
- Use stones designed specifically for sauna heaters.
- Choose the stone size recommended for your heater.
- Use the stone load specified by the heater manufacturer.
- Place the stones carefully rather than pouring them in.
- Leave enough space for airflow.
- Pour water onto hot stones, not exposed heating elements.
- Check the stones regularly as they crack and settle over time.
- For HUUM heaters, remember the 100/200/400-hour maintenance rule: inspect, rearrange, replace.
1. Why are there stones in sauna heaters?
Why are there stones in sauna heaters? Their main job is to store heat and release it gradually into the sauna.
The stone mass acts as a buffer between the heating elements and the room. Instead of heat coming only from the elements themselves, the rocks absorb energy and help distribute warmth more evenly.
The stones are also essential for creating leil. When water is poured onto hot sauna rocks, the stored heat causes the water to evaporate, creating the characteristic hot, humid wave of air associated with traditional sauna bathing.
Different sauna heaters are designed for different stone loads. The correct stone load is always determined by the heater design, so more stones do not automatically mean better performance.
2. What are the best sauna stones?
What are the best sauna stones? The best sauna stones are durable, heat-resistant natural stones designed specifically for use in a sauna heater.
The stone type matters because sauna stones are repeatedly exposed to high temperatures and sudden cooling when water is poured over them. Unsuitable stones may crack, crumble, or deteriorate quickly.
HUUM recommends natural sauna stones such as olivine diabase or olivine. HUUM’s own olivine diabase stones are durable and well suited to repeated heating and cooling.
HUUM sauna stones are available in two sizes, 3–5 cm and 5–10 cm, depending on the heater model.
Decorative stones should not replace the main stone load unless they are specifically suitable for sauna heaters. Likewise, random stones collected from nature are not a reliable substitute for proper sauna stones unless their composition and heat resistance are known.
3. How many sauna stones do I need?
How many sauna stones do I need? The correct amount depends on the specified stone load of your sauna heater.
Different heaters are designed for very different amounts of stone, so always follow the manufacturer’s instructions.
HUUM heaters vary considerably in stone capacity. For example:
- CORE: around 40 kg
- CLIFF: around 75 kg
- HIVE Mini: around 150 kg
- HIVE: around 250 kg
These differences reflect the construction and intended performance of each heater.
Do not add extra stones simply to increase the stone mass. Overfilling the heater can restrict airflow, while too few stones may leave heating elements exposed.
For the best result, use the recommended stone load, stone size, and stacking method for your specific heater.
If you are still choosing the heater itself, stone capacity is only one part of the equation. The heater must also have the right power for the size and construction of the sauna. Read more in HUUM’s guide on how to dimension a sauna heater.
4. Why does stone mass matter in a sauna heater?
Why does stone mass matter in a sauna heater? Stone mass affects how much heat the heater can store and how steadily that heat is released.
A greater stone mass can store more thermal energy, which is one reason heaters with substantial stone capacity are often associated with a softer and more enveloping leil.
This stored heat also helps the stones recover between pours of water. In simple terms, the stones function like a thermal battery: they store heat when the heater is running and release it gradually during the sauna session.
However, the correct stone mass is always linked to the heater’s design. Adding more stones than recommended can restrict airflow and slow heating.
The goal is not to fit as many stones as possible into the heater, but to use the stone load the heater was designed for.
5. What size sauna stones should I use?
What size sauna stones should I use? The right size depends on the sauna heater model and its construction.
HUUM sauna stones are available in two main sizes:
- 3–5 cm
- 5–10 cm
Different HUUM heaters require different stone sizes. For example, CLIFF uses smaller 3–5 cm stones, while models such as CORE and HIVE use 5–10 cm stones.
Using the correct size helps the stones fit properly around the heating elements while leaving enough room for air to move through the heater.
Always follow the stone size specified for your particular sauna heater.
6. Why does HUUM recommend round sauna stones?
Why does HUUM recommend round sauna stones? HUUM recommends them because their rounded shape allows water to move more freely into the lower layers of the heater.
Instead of evaporating only on the uppermost rocks, water can travel between the rounded stones and reach hot surfaces deeper inside the stone mass.
This helps more of the stored heat contribute to the leil and can create a softer, more gradual experience.
Round stones also complement HUUM’s open-design heaters, where the stones form an important part of the heater’s visual character.
7. How should sauna rocks be stacked?
How should sauna rocks be stacked? Properly stacked sauna rocks are essential for good airflow and reliable heater performance.
Place the stones into the heater carefully rather than pouring or throwing them in randomly.
Arrange them between and around the heating elements without forcing, pressing, or bending the elements. The stones should sit securely while still leaving enough room for air to circulate through the heater.
The heating elements should also be properly covered. Pouring water directly onto exposed elements can shorten their lifespan and create an excessively sharp burst of heat.
After stacking, check that the stones are stable and that the recommended stone load has been reached.
Over time, stones settle and compact, which is why restacking is an important part of regular heater care. For a more detailed routine, see HUUM’s complete guide to sauna heater, stone, and heating element maintenance.
8. Should sauna stones be washed before use?
Should sauna stones be washed before use? Yes, sauna stones should be rinsed before installation to remove dust and loose particles.
HUUM recommends washing the stones under running water before placing them into the heater.
There is no need to use detergents or cleaning chemicals. Clean water is enough.
Once the stones have been rinsed, allow excess water to drain and place them into the heater according to the instructions for your particular model.
9. Can you pour water on sauna stones?
Can you pour water on sauna stones? Yes – pouring water onto properly heated sauna stones is what creates leil.
When water reaches hot rocks, the stored heat causes the water to evaporate. This temporarily increases the humidity and changes how the heat feels on the skin.
Rather than pouring a large amount of water at once, add it gradually and allow the stones time to recover between pours. This gives you greater control over the intensity of the leil.
Water should be poured onto the hot sauna stones rather than directly onto exposed heating elements.
And yes, this applies to electric sauna heaters too. The idea that you cannot pour water onto an electric heater is a common sauna misconception. Read more about this and other common misconceptions in 3 sauna myths that affect your sauna experience.
Use clean water and always follow the heater manufacturer’s instructions.
10. How often should sauna stones be replaced?
How often should sauna stones be replaced? The replacement interval depends on how much the sauna is used, but regular inspection is just as important as replacement.
Repeated heating and cooling gradually cause sauna rocks to crack, settle, and deteriorate.
For HUUM heaters, a simple way to remember stone maintenance is:
The HUUM 100/200/400-hour rule
- 100 hours – inspect the stones
- 200 hours – rearrange the stones and replace damaged ones
- 400 hours – replace all sauna stones
Following this schedule helps maintain airflow and reduce unnecessary stress on the heating elements.
When maintaining the heater, remove the stones, clear away stone dust and fragments, inspect them individually, and discard damaged pieces before restacking.
For frequent sauna users, these maintenance intervals may arrive much sooner than expected.
For step-by-step instructions, see HUUM’s sauna heater maintenance guide.
11. How do you know when sauna rocks need replacing?
How do you know when sauna rocks need replacing? Look for cracking, crumbling, excessive stone dust, tightly packed stones, or changes in heater performance.
One of the clearest warning signs is stone dust or small fragments collecting at the bottom of the heater.
A change in sauna performance can also be a clue.
If your sauna suddenly takes longer to heat, do not immediately assume the heater is the problem – check the stones first.
5 signs your sauna stones need attention
- The sauna takes longer to heat than usual.
- The leil feels weaker or less consistent.
- You see stone dust or fragments inside the heater.
- The stones are cracked or crumbling.
- The stone layer has settled and become tightly packed.
If you notice these signs, remove and inspect the stones. Replace damaged ones, clear loose debris from the heater, and restack the remaining sauna rocks correctly.
Do not wait until every stone is visibly broken. Regular inspection and timely replacement help maintain the performance of the sauna heater.
Take care of your sauna stones for better leil
Taking care of your sauna stones helps preserve efficient heating and consistent leil.
Choose stones designed for sauna use and use the size recommended for your heater. Wash them before installation, stack them carefully, and inspect them regularly as they age.
For HUUM heaters, choose the appropriate natural olivine diabase sauna stones and remember the 100/200/400-hour maintenance rule.
Good sauna stones may seem like a small detail, but they play a central role in turning the heat of the heater into the soft, satisfying leil that makes a sauna feel complete.
