By The Sauna Company · Published 6 Nov 2026
Good sauna steam combines clean air, the right temperature, the right moisture and radiant heat from the stones and walls. Fresh air comes first: a sealed sauna fills with exhaled CO2, and adding steam does not fix that. A heater with a large stone mass gives softer, longer-lasting steam.
Good sauna steam turn is more than the hiss when water hits the stones. It is the purity, temperature and moisture content of the air in the sauna, together with the radiant heat from the stones and walls.
Steam ladled into stale, CO2-heavy air is just steam in stale air. That is why ventilation decides whether a sauna ever gives you good steam.
Key takeaways
- Four parts. Good sauna steam combines clean air, the right temperature, the right moisture and radiant heat from the stones and walls.
- Fresh air comes first. A sealed sauna fills with exhaled CO2, and adding steam does not fix that.
- Stones matter. A heater with a large stone mass produces softer, longer-lasting steam.
- Ventilation is calculated, not guessed. It is the most important part of sauna design.
- Smells spoil it. Perfume, odours and stuffy air all spoil the steam, however good the heater.
What does good sauna steam feel like?
In Finland, saunas are judged on the burst of steam that rises when you throw water on the hot stones, and the wave of heat you feel a second later on your shoulders.
Good steam is soft, even and lasting. Bad steam bites, scalds your ears and vanishes, or leaves the room feeling heavy and airless.
Our sauna steam page quotes a 1988 paper on sauna and health that defines good sauna steam as the purity, temperature and moisture content of the air inside the sauna, together with its thermal radiation. The same paper adds: "The purity of the sauna air is ensured primarily by effective ventilation."
What are the four parts of good sauna steam?
- Purity. Fresh air, not stale from exhaled CO2, and free of perfumes and odours. This is the part most home saunas get wrong.
- Temperature. In a traditional Finnish sauna (Aqua Spazio Sana) the air at the ceiling sits at 75–95°C. Too cool and the steam feels damp; too hot and it stings.
- Moisture. A traditional sauna runs at around 5–15% humidity between ladles. Each ladle of water lifts it briefly, and that rise is what you feel as a wave of steam. Our post on humidity control in a sauna covers hygrometers and how to manage it.
- Thermal radiation. The radiant warmth from the heater, the stones and the timber walls. This is why stone mass and timber choice matter, not just heater output.
Why doesn't steam on stale air work?
Every breath you exhale carries roughly 40,000–60,000 ppm of CO2. The UK Health and Safety Executive puts normal air at about 0.037% CO2, which is around 370 ppm. In a small, closed, hot room with two or three people breathing hard, the gap between those numbers closes quickly unless fresh air comes in and stale air goes out.
That build-up matters even at modest levels. In a controlled study published in Environmental Health Perspectives in 2012, Satish and colleagues found that people at 1,000 ppm CO2 scored moderately but significantly lower on six of nine decision-making measures than at 600 ppm, with larger drops at 2,500 ppm. The authors noted the findings need confirming, but the direction is clear.
At higher concentrations, the HSE lists headaches, dizziness and confusion among the effects of CO2. This is why people sometimes come out of a badly built sauna feeling light-headed and assume it was the heat.
You can ladle as much water as you like onto the stones; you are adding moisture to air that is already tired. As our sauna steam page puts it, steam added to stale air is just that: steam added to stale air.
How is a sauna designed for good steam?
Jesse Hämäläinen of Narvi Sauna Heaters in Finland summed it up in 2012, in a line we quote on our sauna steam page: there is no shortcut to perfect sauna steam, and it always comes down to stones and proper ventilation.
Ventilation first. Our primary design goal is effective ventilation to remove excess CO2, followed by air circulation that keeps the temperature difference between the upper and lower layers of air as small as possible. Heater manufacturer Harvia recommends six air changes per hour for a sauna with an electric heater, with vent positions depending on whether ventilation is mechanical or gravity-driven.
With every sauna design we supply calculations of air volume, heat loss and heater capacity, plus drawings for the ventilation fittings layout.
Stones and heater. A heater with a generous stone mass stores more heat and releases steam more gently. HUUM, for example, says its CLIFF heater uses a large amount of stones for mild, long-lasting steam.
Even heat. In many saunas the top bench is too hot and the lower bench too cold, with stale air at head height. Climate control such as the Saunum Base, used in our climate-controlled saunas (Aqua Spazio Saunum), mixes hot air from the upper level with cooler air from floor level so the temperature is more even.
No perfume, no odours. Strong scents and musty timber both spoil the air. Good ventilation also helps the sauna dry out after use, which keeps mould and odours away.
What did we build in Islington?
In an Islington basement bathroom, the client's brief for a compact two-seater became a full-size sauna in the same space, without moving much of the bathroom furniture. We integrated a HARVIA CILINDRO 9kW heater into an L-shaped lower bench, which frees up floor space while keeping a substantial 80kg of stones for steam.
The 2+1 bench layout has a floating top bench 500mm wide, behind an 8mm clear glass door, with a slimline vapour barrier and XENIO Wi-Fi control.
Frequently asked questions
What makes good sauna steam?
Good sauna steam depends on the purity, temperature and moisture content of the sauna air together with radiant heat from the stones and walls. Steam alone, added to stale air, is not good steam.
Why do I feel dizzy in some saunas?
In a poorly ventilated sauna, exhaled CO2 builds up, and raised CO2 is linked to dizziness, headaches and confusion. Heat and dehydration also play a part, so drink water, keep sessions to 15–20 minutes and leave if you feel unwell.
Does an infrared sauna produce steam?
No. Infrared saunas (Aqua Spazio Radiata) heat the body with panels and have no stones to ladle water onto. If you want real steam with infrared benefits, a hybrid sauna (Aqua Spazio Hybrid) combines a traditional stone heater with ceiling infrared panels.
Do more stones mean better steam?
Generally, a larger stone mass stores more heat and releases gentler, longer-lasting steam. Stones crack and crumble with use, so we recommend replacing them annually.
Talk to a sauna designer
Every sauna we build starts with the airflow. Book a free design consultation, or email photographs and dimensions of your space to www.saunacompany.co.uk for an initial assessment. Read more on our sauna steam page.
Planning one for your own home? See our traditional Finnish saunas page for options and recent projects, or book a free design consultation and we'll talk through your space.
What spoils sauna steam?
Perfume, odours and stuffy air all spoil the steam, however good the heater. Fresh air comes first: a sealed sauna fills with exhaled CO2, and adding steam does not fix that.
Sources
- Environmental Health Perspectives — Satish et al. (2012), "Is CO2 an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance". Decision-making declines at 1,000 and 2,500 ppm CO2 compared with 600 ppm.
- HSE — General hazards of carbon dioxide. Normal atmospheric CO2 of about 0.037% and symptoms at raised levels.
- Harvia — Ventilation in the sauna. Six air changes per hour and vent placement.
- HUUM — CLIFF electric sauna heater. Large stone capacity for mild, long-lasting steam.