Humidity Controls on Heaters and Generators

How humidity works in a sauna

Humidity is the amount of water vapor in the air. In a sauna, it determines whether you feel dry heat or wet heat. Traditional saunas typically run at less than 20% relative humidity, according to Cleveland Clinic. Steam rooms, on the other hand, use high humidity to create a moist environment. Understanding this difference helps you choose how to manage humidity in your own setup.

Relative humidity is measured with a hygrometer. A traditional sauna heater with exposed stones lets you add water to create a quick burst of steam, known as loyly. A steam generator pushes steam through a line into the room, raising humidity continuously. For a deeper look at these terms, see what is relative humidity in a hot room and what a hygrometer measures.

Water: the traditional way to raise humidity

In a traditional sauna, you control humidity by pouring water on hot stones. Finnleo recommends sprinkling one ladle of water at a time; pouring or dumping water is not advised, and a clear sign you used too much is water leaking out the bottom of the heater. This manual method gives you direct control over each burst of steam.

For infrared saunas, humidity is ambient and no water should be added, as stated by Finnleo. If you have an infrared cabin, do not pour water on the heating panels. See how to pour water on stones and water on infrared heaters warning for more.

Vents: letting humidity escape

Ventilation is the passive side of humidity control. Fresh air intake and exhaust vents allow moisture to leave the room, preventing the air from becoming too heavy or stuffy. In a traditional sauna, a small vent near the heater and another higher on the opposite wall can keep air moving without removing all the heat.

In a steam shower, ceiling vents inside the enclosure are not recommended or necessary, according to Amerec. Instead, an exhaust fan outside the steam door removes excess moisture when you open the door. Learn more in sauna ventilation basics and sauna vent placement traditional.

Common vent placements:

- Low intake near the heater to bring fresh air

- High exhaust opposite the heater to pull out moisture

- Adjustable covers to control airflow without losing heat

• Low intake near the heater to bring fresh air
• High exhaust opposite the heater to pull out moisture
• Adjustable covers to control airflow without losing heat

Sensors and automated controllers

Some sauna and steam systems include electronic sensors that measure temperature and humidity, then adjust the heater or generator to hold a set level. For example, many steam generator controls let you program session time and temperature, and some models include a hygrometer to maintain a target humidity. These features are common on steam systems from manufacturers like MrSteam and Amerec.

If you want to monitor humidity without electronics, a mechanical hygrometer is a simple option. Digital combo thermo-hygrometers also display temperature and humidity in one unit. For a deeper understanding of how controllers work, see sauna control panel types and what is a sauna thermostat vs controller.

Digital controls often let you set a humidity target, and the system uses a sensor to cycle the heater or generator on and off to maintain that level. For steam generators, this is especially useful because the room fills with steam quickly. Some systems also include a timer and a delayed start, so you can schedule your session. These features add convenience but also require a more complex control board, which may be harder to replace. Consider how often you will use the presets and whether you prefer a simple dial or a touchscreen.

Steam generators: humidity on demand

Steam generators are designed for steam showers and steam rooms. They heat water in a tank and send steam through a copper line to a steam head mounted in the enclosure. Amerec recommends placing the steam head 18 inches above the floor, away from bathers, to minimize contact with hot steam. The generator is controlled by a panel that may include options for temperature, aroma, and lighting, as seen in MrSteam controls like the iSteam3 or AirTempo.

Because steam generators produce steam continuously, humidity rises quickly. They require a cold water supply and a drain line for maintenance, per Amerec. For more on the difference between these systems and sauna heaters, see steam generator vs sauna heater and what is a steam generator term.

What to consider when choosing a humidity system

Your choice comes down to how wet you like your heat. If you enjoy a dry Finnish sauna with occasional bursts of loyly, a traditional heater with an open stone compartment and a manual ladle is enough. If you prefer a constant, enveloping steam bath, a steam generator with a programmable control is the way to go. Infrared saunas require no water system at all.

Also consider maintenance. Steam generators need periodic flushing or an auto-drain option to prevent scale buildup, as noted by Amerec and MrSteam. Traditional saunas only need the stones and a good cleaning. Weigh these factors against your daily routine. For more, see dry sauna vs wet sauna and steam room vs sauna vs steam shower.

What to pick for your use

Questions

Can I add water to an infrared sauna to raise humidity?

No. Finnleo states that for infrared saunas, humidity is ambient and no water should be added. Pouring water on infrared panels can damage them and is not part of the intended use.

What is the typical humidity level in a traditional sauna?

According to Cleveland Clinic, traditional saunas usually have low humidity, about less than 20%. You can raise it temporarily by pouring water on the stones, but the air remains dry compared to a steam room.

How does a steam generator control humidity?

A steam generator continuously produces steam, so the humidity is inherently high. The control panel sets the steam output and session time; some advanced controls include a humidity sensor to maintain a specific level.

Do I need a vent inside my steam shower?

Amerec recommends against ceiling vents inside a steam enclosure. Instead, install an exhaust fan outside the steam door to clear excess moisture when you exit.

What is loyly and why does it matter?

Loyly is the burst of steam created when you toss water onto hot sauna stones. It raises humidity and adds a characteristic sensation to the heat.