Advanced Guide on Sauna Ventilation

Ventilation plays a crucial role in a sauna because it’s all about our breathing. When several people are enclosed in a small sauna room, the accumulation of exhaled CO2 rapidly reaches unhealthy levels, disrupting the sauna experience. The primary goal of ventilation is to eliminate excess CO2 from the sauna environment.

General Setup Guide

Wood Heater Fed from Inside

Optional setup: You can have all 3, options 1 and 2 or options 1 and 3.

Adjustable fresh air supplies or ventilation materials

1. Above the heater. - This system ensures bathers have access to fresh air (oxygen) while effectively removing CO2, excess humidity, and other impurities. It's best if this ventilation is adjustable, sourced from outside, and equipped with a backflow prevention device. Additionally, including an updraft duct or a mechanical blower may be advisable.
2. Below the foot bench on a wall opposite the heater. - This opening is utilized at the end of the sauna session to allow excess moisture to escape. It's typically positioned in or near the ceiling diagonally opposite to the heater.
3. Near the floor behind/below the heater. - This feature ensures there's ample combustion air for the fire and should be adjustable to control the airflow.

Electric Heater and Wood Heater Fed from Outside

Optional setup: You can have all 4, or combinations of 1 to 4.

Adjustable fresh air supplies or ventilation materials

1. Above the heater. - This system ensures bathers have access to fresh air (oxygen) while effectively removing CO2, excess humidity, and other impurities. It's best if this ventilation is adjustable, sourced from outside, and equipped with a backflow prevention device. Additionally, including an updraft duct or a mechanical blower may be advisable.
2. Cooling Air Supply for High-Temperature Sensor Behind or Below the Heater. - This system is designed to supply air to cool down the sensor, which is usually found in heaters certified by UL. Its purpose is to prevent the high-temperature limiter from accidentally triggering. It's essential for this airflow to be adjustable and regulated to just the right amount needed to keep the sensor from tripping.
3. Opening a natural exhaust vent in the corner opposite to the heater. - Typically situated near or in the ceiling, serves to expel excess moisture once sauna usage concludes for the day. As an alternative, leaving the exhaust blower operational for approximately 2 hours proves more effective in thoroughly clearing out moisture from the sauna.
4. Mechanical exhaust system positioned below the foot bench.

Ventilation Necessity

Good ventilation is crucial for regulating humidity levels in the sauna. Just as we appreciate the alternating cycles of hot and cold, we also seek a balance between humid and dry conditions. When water is thrown on the stones, it increases humidity temporarily. However, efficient ventilation ensures that this excess humidity is promptly removed, restoring the overall humidity to its previous level. This cycle ensures that each subsequent throw of water yields the same level of humidity increase, maintaining a consistently comfortable environment.

Proper ventilation not only aids in preventing windows from fogging up but also plays a crucial role in removing excess humidity during sauna sessions. Without adequate ventilation, repeated throws of water on the stones can lead to an accumulation of humidity over time.

Elimination of various other odors, VOCs, and pathogens is also crucial. While hot air is a natural occurrence, it's not something we want lingering in the sauna environment.

The presence of cooler air serves another vital purpose: it ensures that the components of an electric heater activate frequently enough to maintain the stones at an optimal temperature for generating steam. Without this flow of cooler air, the sauna may retain excessive heat, resulting in infrequent activation of the heater.

Options for Ventilation

There are 3 semi-effective ventilation strategies to consider.

1. Natural Updraft - This method involves introducing fresh air from below the heater, usually positioned beneath the heater or sometimes below the door or behind it. The exhaust typically exits through the ceiling or, above the floor on the opposite wall.
2. Mechanical Updraft - Similar to the Natural Updraft method described above, but instead of relying on natural convection for exhaust, a mechanical system is employed, usually consisting of an electric duct blower.
3. Mechanical Downdraft - In this system, fresh supply air enters above the heater, while mechanical exhaust occurs below the foot bench, often facilitated by an inline duct blower. This approach is advocated in Finland and other regions.

Mechanical Downdraft stands out as the most effective option among the three for providing ventilation. It's backed by physics and studies conducted by VTT confirm its efficacy. Sauna builders in Finland consistently recommend this approach. VTT has been advocating for mechanical downdraft since their research in 1992, which demonstrated it as the best and most practical option available.

There are valid reasons behind this choice:

• Cold air naturally sinks - When it enters below or behind a heater, it doesn't primarily flow upward into the heater as commonly assumed. Instead, only a fraction goes up into the heater, a bit more envelops bathers' feet, but the majority simply moves across the floor and exits through the exhaust, offering minimal benefit. However, when fresh air enters above the heater, it becomes entrained in the rising heat and convective loop. This allows it to disperse evenly throughout the sauna, carrying away CO2, before ultimately exiting.
• Natural convection is not a dependable solution - In electrically heated saunas, relying solely on natural convection rarely produces adequate airflow, and sometimes, there's no airflow at all. Unlike wood-fired saunas where the heater naturally creates enough exhaust airflow, electrically heated saunas (and wood-fired ones with external combustion air) require a blower to ensure consistent and sufficient removal of stale air.

2 distinct temperature sensors: the Thermostat Sensor and the High-Temp Sensor.

1. Thermostat Sensor is responsible for regulating the overall temperature inside the sauna. Typically mounted above the heater or on the sauna wall, it ensures that the sauna temperature stays within the desired range. The Thermostat Control, usually located outside the sauna or on the heater's face, allows users to adjust the temperature setting.
2. High-Temp Sensor is usually positioned on or inside the electric heater. When it detects heat levels surpassing its preset threshold, it triggers the HL Switch (High Limit Switch, Overheat Protection Switch, or Thermal Protection Switch), shutting off the heater. To reset the HL Switch after a trip, users must wait until the High-Temp Sensor cools below its set point. This sensor is a mandatory requirement for electric heaters in North America, absent in heaters used in Finland, Sweden, and other regions.

Conclusion

Proper ventilation is essential for maintaining a healthy and comfortable sauna environment. Whether it's removing excess CO2, controlling humidity levels, or ensuring adequate airflow, ventilation plays a crucial role in optimizing the sauna experience. From natural convection to mechanical downdraft systems, there are various ventilation options available, each with its advantages and considerations. Understanding the importance of ventilation and selecting the appropriate system for your sauna setup can greatly enhance the enjoyment and effectiveness of your sauna sessions. So, whether you're designing a new sauna or retrofitting an existing one, prioritizing ventilation is key to creating a rejuvenating and enjoyable sauna experience for all users.