What is thermal stratification in a sauna?

In simple terms, thermal stratification occurs when hot and cold air fail to mix properly, causing hot air to gather at the top while cold air remains at the bottom. A high-quality sauna should minimize or eliminate this issue. We are confident that our outdoor electric sauna is one of the best available on the market. To address thermal stratification, we have integrated large, adjustable vents to ensure proper airflow, maintaining optimal oxygen levels and promoting even mixing of hot and cold air for a superior sauna experience.

As air heats up, it creates pressure that prevents the cooler, low-pressure air from mixing evenly, similar to what you feel on a hot summer day when swimming in a lake: the top layer of water is warm, but the water near your feet is cold. The same principle applies to saunas: hot and cold air don’t naturally mix. To warm your feet, they need to be elevated into the warm air. We’ve designed our sauna with this in mind, ensuring your feet are positioned as high as possible relative to the space of the sauna and the height of the benches.

Many diagrams online suggest that cold air enters through a lower vent, rises with the heat, and exits through an upper vent. However, this is not how it works in practice. If there are gaps under the door or in the floor, the air from the lower vent will mix with the air entering through those gaps, instead of rising to mix with the hot air. Due to the pressure difference, the fresh air won’t reach the upper part of the sauna. As a result, you may end up rebreathing CO2 instead of getting fresh oxygen. We understand this, and so in our saunas, we’ve incorporated three times the number of vents to make sure you have plenty of fresh oxygen.

In a poorly designed sauna, you may experience what we call "cold feet syndrome," where your upper body enjoys the warmth, but your feet stay cold. This is a common issue in barrel saunas and other designs with benches that are set too low.