Löyly, Explained: What the Stones Actually Do in Every Sauna Type

The moment you throw water on hot stones and hear the hiss—that's löyly, and it works exactly the same way in a gas sauna, a wood-fired sauna, and an electric sauna. Stones don't make a heater type "real" or "fake." They have one job: hold thermal energy and release it as steam when water is poured on them. All sauna types include stones; all produce löyly. The misconception that gas saunas can't do löyly (because they're "not a real sauna") is a marketing myth with no basis in physics. A FinSteam Botnia or Aurora heater comes with an Orbis cage containing approximately 40 kg of hot stones, ready to produce authentic löyly in every session—the same experience as a wood-fired or electric sauna, just without the wait or electrician.

What löyly actually is—the physics

Löyly (pronounced "LOY-loo") is the sensation of steam released when water contacts very hot rocks or metal surfaces in a hot sauna. It's purely physics: water evaporates rapidly due to the high temperature (above 100°C at the stone surface, even though the air is 80–90°C), creating steam that humidifies and heats the air around you.

The sensation is intense because steam transfers heat more efficiently to skin than dry air. Touching hot air at 85°C is bearable; touching steam at the same temperature feels scalding. This is why löyly feels like a deep, penetrating heat—it's humidity doing real thermal work.

There is nothing mysterious or exclusive about this. Any hot object (stone, metal, or ceramic) can produce löyly if you throw water on it. The mechanism is identical across all sauna types.

What role do stones play in a gas sauna?

In a gas sauna with Direct Thermal Flow™, stones are NOT the primary heat source. Instead, they have two distinct functions:

First, thermal participation: stones absorb heat from the combustion air and the ambient environment. They warm up over 10–15 minutes and participate in the overall sauna thermal balance, contributing to the room's heat capacity.

Second, löyly production: once heated, the stones hold energy and release it as steam when water is thrown on them. This creates the authentic löyly experience—that burst of intense moist heat that defines a sauna session.

In contrast, a wood-fired or electric sauna uses stones as PRIMARY thermal storage. The heater (fire or element) warms the large stone mass, and the mass slowly releases that energy into the room over hours. Stones are the buffer, the thermal battery. In a gas sauna, stones are participants, not batteries.

Why FinSteam uses the Orbis cage and 40 kg of stones

The FinSteam Orbis cage holds approximately 40 kg of sauna stones. This is enough to:

• Create robust löyly when water is thrown (thick steam, not a thin wisp).
• Participate meaningfully in the sauna's thermal balance and heat retention during use.
• Provide thermal mass that holds heat during the session, reducing the burner's cycling.

40 kg is not excessive (some wood stoves have 100+ kg), and it's not minimal (a tiny stone pile wouldn't produce satisfying löyly). It's practical: enough to feel like a "real sauna" and enough to create authentic steam, without being so heavy that the cage becomes cumbersome to move or clean.

The Orbis cage is specifically engineered to sit directly in the heater's exhaust stream, allowing hot air to circulate through the stones efficiently. This means the stones heat up faster than they would in a wood sauna (where they depend on the slow radiant heat from the stove body) and release energy directly into the sauna air.

Löyly in gas saunas vs. wood-fired vs. electric

Gas sauna löyly: Water hits hot stones in the Orbis cage. Steam rises instantly and fills the sauna. The sensation is sharp and immediate because the air temperature is already high (85–90°C) and the water is evaporating into 100% saturated steam.

Wood-fired sauna löyly: Water hits the large thermal-mass stove. Steam rises, but the sensation can feel "softer" because the ambient air temperature is lower initially (the heater's outer surface is not as hot as the fire inside). The stone mass holds water longer, allowing slower steam release.

Electric sauna löyly: Water hits stones or metal around an electric element. Steam is produced and released. The sensation is sharp because the air temperature is already high (like gas), but the stone mass is smaller (elements can't accommodate huge stone piles), so the löyly burst is shorter-lived.

In real-world use, all three produce authentic löyly. The differences are in intensity and duration, not in the fundamental physics. If someone has experienced löyly in a wood sauna, they will recognize löyly in a gas sauna immediately—it's the same sensation, from the same mechanism, on the same hot stones.

The myth: "Gas saunas can't do löyly because they're not traditional"

This claim conflates "traditional" with "physically functional." Traditional saunas used wood because it was available and culturally established. But the physics of löyly—water on hot stone = steam—is universal.

The myth persists because:

• Some older gas patio heaters (not sauna heaters) lacked stones, so people assumed all gas heat can't produce löyly. False. A sauna heater with stones (like FinSteam) produces löyly normally.
• Marketing from wood and electric sauna sellers emphasizes tradition, implying modern gas is "inauthentic." This is rhetoric, not reality.
• Lack of UK awareness: gas saunas are new to the UK market (FinSteam is the first CE-certified electricity-free gas sauna heater in Europe), so people haven't experienced one yet.

The test is simple: heat stones to 200°C+ and throw water on them. Löyly happens. The heater's fuel source (wood, electric, gas) is irrelevant to the chemistry of water evaporation.

Stone maintenance and refresh in gas saunas

Hot stones eventually crack and degrade due to thermal cycling (heating and cooling) and water impact (throwing cold water onto hot stone creates stress). This is normal in all sauna types.

FinSteam stones can be replaced via the accessories page, where individual stones (£99) and replacement Orbis cages are available. Refreshing stones every 2–3 years of regular use is typical for any sauna—not a gas-specific issue.

The durability of FinSteam stones is comparable to wood or electric sauna stones because they're the same product, undergoing the same thermal stress. Stone degradation is universal to all sauna types, not a weakness of gas heating.

Why stones matter psychologically (and physically)

Stones are the ritual object of sauna culture. The act of throwing water on stones, hearing the hiss, feeling the steam rise—this is sauna. It's the experience that separates a sauna from a hot room.

By including a full complement of stones and a robust cage, FinSteam makes gas saunas feel like genuine saunas, not stripped-down alternatives. You get the ritual, the sensation, the authentic experience—plus the practical benefits of no electrician, fast heat-up, and flueless energy retention.

This is why the claim "gas saunas aren't real saunas" fails. Stones and löyly are universal. Gas saunas have them. Therefore, gas saunas are real saunas. End of discussion.

Sources

Sauna engineering and stone specifications (Finnish sauna manufacturers and standards); FinSteam Orbis cage and stone load data (product specifications, 2026); sauna tradition and cultural literature (Finnish sauna foundation publications); thermodynamics of water evaporation and löyly physics (standard heating engineering texts).