Humidity Balance™: Why Gas Saunas Never Feel Bone-Dry

Electric saunas start bone-dry. Heat the air and add water via löyly (stones), and the humidity rises. Gas saunas are different: combustion itself produces water vapour continuously. The chemistry is simple: propane (C₃H₈) + oxygen → carbon dioxide + water (C₃H₈ + 5O₂ → 3CO₂ + 4H₂O). This produces 1.5 litres or more of water vapour per kilogram of gas burned—a gentle, continuous addition to the sauna air. The result is Humidity Balance™: a pleasant base humidity that sits underneath traditional löyly. You throw water on stones and get löyly exactly as normal, but the sauna doesn't feel desert-dry before you do. This misconception—that gas saunas are "fake saunas" without humidity—is physics nonsense and marketing myth.

The combustion chemistry behind Humidity Balance™

When LPG (liquid petroleum gas, mainly propane) burns in an 8.1 kW FinSteam burner, the reaction is complete combustion of propane:

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

This equation tells you exactly what's produced: three molecules of carbon dioxide (CO₂) and four molecules of water (H₂O) for every molecule of propane burned. Water is not a pollutant or byproduct to be ashamed of—it's a legitimate product of the reaction, and in a flueless sauna, it stays inside the room as vapour.

The quantity is significant. One kilogram of propane produces approximately 1.5 litres (or more, depending on condensation) of water vapour. An 8.1 kW heater burning continuously produces roughly 0.6 kg of gas per hour, which equals ~0.9 litres of water vapour per hour of continuous burning.

In a typical 15–20 minute heat-up session, that's roughly 0.2–0.3 litres of vapour already in the air before anyone throws water on stones. It's not a huge amount, but it's enough to prevent the sauna from feeling like a hair dryer.

What Humidity Balance™ feels like

An electric sauna heater at 85°C with no water thrown yet feels dry to the skin. Your mucous membranes dry out. The air feels harsh. This is because the air temperature is high but the absolute humidity (actual water content) is very low.

A gas sauna at 85°C, with gentle base humidity from combustion, feels different: less harsh, more pleasant. The skin and respiratory tract don't dry out as quickly. The sauna feels "alive" compared to electric's clinical dryness.

This is not the difference between "bone-dry" and "steamy"—that's löyly, which works the same way in all sauna types. This is the difference between "harshly dry" and "gently warm with a hint of moisture."

How Humidity Balance™ coexists with löyly

Humidity Balance™ and löyly are separate mechanisms. Don't confuse them.

Humidity Balance™ is the continuous background humidity produced by combustion and captured inside the flueless sauna. It's always present as long as the heater runs.

Löyly is the burst of steam you get when you throw water on hot stones. The water evaporates instantly and creates a temporary spike in humidity and radiant heat. This works in all sauna types—electric, wood, or gas—because it's just physics: hot stones + water = steam.

In a gas sauna, löyly works exactly as normal. You get the same steam rush, the same deep heat penetration into your muscles, the same authentic sauna sensation. The difference is that the baseline humidity is already higher, so the experience feels less artificially dry.

Why this matters for comfort and health claims

Dry air is uncomfortable. Prolonged exposure to very dry heat (below 10% relative humidity) irritates airways and dries skin. A sauna at 85°C with no humidity can quickly become unpleasant, which is why sauna users almost always throw water to create löyly.

By starting at a higher baseline humidity, a gas sauna allows more flexibility. You can enjoy the session with or without löyly. If you just want dry heat for detoxification or muscle relaxation, you can sit without throwing water—and it won't be aggressively drying because the combustion vapour is already there.

If you want traditional humid löyly, throw water as normal. Nothing changes in the experience.

This is not a medical claim (saunas don't "cure" anything), but it is a comfort reality: Humidity Balance™ makes gas saunas usable for longer periods without the harsh dryness of electric.

The myth: "Gas saunas aren't real saunas because they're dry"

This myth comes from a misunderstanding of flueless combustion. Some people assume that because a gas heater doesn't use stones as the primary thermal mass, it can't produce humidity. Wrong.

Other misconceptions stem from comparing a gas heater (which runs anywhere) to a commercial electric installation (which is highly engineered and often includes humidity control systems). If you compare a portable gas sauna to a professional spa's electric setup, of course the spa feels better—it's engineered by specialists.

The honest comparison is gas vs. electric in real-world domestic setups. And there, gas wins on comfort because Humidity Balance™ makes the heat feel less harsh.

How combustion chemistry varies across heater types

All combustion produces water as a byproduct. The difference is what happens to it.

Electric heaters: no combustion, no water produced. All humidity comes from löyly only. Baseline is bone-dry.

Wood-fired stoves: produce enormous amounts of water vapour during burning. But the flue sends it all up the chimney. Result: wood saunas often feel dry before löyly, despite producing water. All the vapour is vented outside.

Flued gas heaters (rare in UK): produce water vapour, but the chimney vents it outside, same as wood. You lose the humidity benefit.

Flueless gas heaters (FinSteam, Orbis, others): produce water vapour AND keep it inside. Result: Humidity Balance™—gentle base humidity + normal löyly on top.

Is there a maximum humidity level to worry about?

No, within normal sauna use. The water vapour from a 0.6 kg/h burn rate is small compared to löyly. Even with active water throwing, sauna humidity rarely exceeds 60–70% relative humidity at sauna temperatures (which is already very hot—absolute humidity is still manageable).

High-humidity saunas (>75% RH at 85°C) are called steam baths or steam rooms. A sauna with Humidity Balance™ + regular löyly is well balanced—hot and moist, but not extreme.

If you wanted to run a gas sauna continuously without opening the door or venting, yes, humidity could accumulate. But this isn't normal use. Regular sessions open the door, allowing vapour to escape. Between sessions, ventilation refreshes the air.

Combustion products: CO₂ and CO—why they're safe here

Complete combustion of clean LPG produces CO₂ (carbon dioxide) and H₂O (water). These are safe, non-toxic, and vented continuously via the sauna's mandatory ventilation system.

Incomplete combustion (poor-quality fuel, bad air supply, or maintenance issues) produces CO (carbon monoxide), which is toxic. This is why all flueless gas saunas have Oxygen Depletion Sensors (ODS) that shut the burner off if the room oxygen drops too low (a sign of incomplete combustion). The ODS is non-negotiable safety engineering.

FinSteam heaters are CE-certified and independently tested for safe operation inside enclosed spaces. The Humidity Balance™—the water vapour—is a feature, not a hazard.

Sources

Propane combustion chemistry and stoichiometry (standard chemistry textbooks); LPG composition and water vapour production (UKLPG technical data); FinSteam heater specifications and running data (manufacturer 2026); sauna comfort studies on humidity and thermal sensation (Finnish sauna research literature).