How Does An Outdoor Sauna Work?

Dec 27, 2025

Ever wondered why a garden shed can feel like a mini spa? Outdoor Saunas work by heating an insulated cabin using wood-burning, electric, or infrared systems, adding water to hot stones for löyly steam, and circulating fresh air through ventilation. Keep reading to learn how heat, humidity, airflow, and setup work together for comfort, efficiency, and year-round use.

The Physics of Heat – How Saunas Warm Your Body

An outdoor sauna provides a calm, restorative space that combines heat, steam, and fresh air to support physical and mental wellbeing. Outdoor saunas warm the body through carefully controlled heat transfer.

Depending on the sauna type, this heat is delivered either through hot air and steam or via radiant infrared energy.

Round wooden barrel sauna with front benches and flower planters in garden.

Traditional Saunas: Heating from the Outside In

Traditional outdoor saunas heat the air inside the cabin. This warmed air then transfers heat to the body over time. These saunas use a wood-burning stove or an electric heater. The internal temperature typically ranges from 60°C to 100°C.

The Role of Sauna Stones: Why Thermal Mass is Essential

Sauna stones store heat from the stove and release it gradually. This stored heat stabilises temperatures inside the sauna.

It also allows water to be poured over the stones to create steam.

Convection and Conduction: How the Air Transports Heat

Hot air circulates through the cabin via convection. Direct contact with warm surfaces transfers heat through conduction.

Together, these processes create an even and enveloping warmth.

Creating “Löyly”: How Steam Bursts Temporarily Increase Temperature

Löyly is produced by pouring water over hot stones. This creates a short burst of steam that increases humidity. The heat feels more intense without raising the actual air temperature.

Infrared Saunas: Radiant Heat and Molecular Vibration

Infrared outdoor saunas use a different heating method. Special panels emit infrared waves that warm the body directly. This creates a different sensation compared to traditional saunas.

Direct Body Heating: How Infrared Waves Bypass the Air

Infrared waves pass through the air without heating it. They penetrate the skin and warm the body from within.

Because of this, the surrounding air remains cooler.

Lower Temperatures, Deeper Sweat: The Benefits of Radiant Heat

Infrared saunas operate at lower temperatures than traditional models. Despite this, they still promote a deep sweat. This makes them suitable for people who prefer a gentler heat experience.

Modern outdoor sauna pod with large glass window and open door on decking.

The Core Systems of a Functional Outdoor Sauna

Several systems must work together for an outdoor sauna to function efficiently. These include the heating source, insulation, ventilation, and moisture control. Each system plays a role in comfort, safety, and long-term durability

The Power Source: Wood-Fired vs. Electric Heaters

Outdoor saunas usually rely on either wood-fired or electric heaters. Each option offers a different experience. The choice depends on preference, installation requirements, and maintenance expectations.

Wood-Fired Stoves: The Authentic Air-Intake and Flue System

Wood-fired stoves create a traditional sauna atmosphere. They rely on controlled air intake and a flue system to manage combustion. These stoves require manual operation and regular cleaning.

Electric Heaters: Thermostats, Heating Elements, and 32-Amp Power

Electric heaters use internal elements controlled by thermostats and timers. Many outdoor models require a dedicated 32-amp power supply. This ensures consistent and reliable heating.

Insulation, Ventilation, and the Vapour Barrier

Insulation helps retain heat while reducing energy use. Proper ventilation ensures fresh air circulation and moisture control. Together, these systems protect the sauna structure and improve comfort.

Managing Airflow: The “Low Intake” and “High Exhaust” Rule

Airflow follows a simple principle. Fresh air enters through a low intake vent, while warm, moist air exits through a high exhaust vent. This balance maintains air quality and prevents excessive humidity buildup

The Aluminium Foil Vapour Barrier: Protecting the Wood from Rot

A vapour barrier prevents moisture from reaching the wooden structure. Aluminium foil barriers are commonly used for this purpose.

They help reduce the risk of rot and long-term damage.

The 2.5m Rule: How External Sizing Affects Heat Efficiency

Larger saunas require more energy to heat. Structures exceeding 2.5 metres in height or width may lose heat more quickly.

Correct sizing improves efficiency and shortens warm-up times.

Operating an Outdoor Sauna for Maximum Benefit

How you operate your sauna affects both comfort and performance. Pre-heating and proper temperature control are essential.

Regular care also extends the life of the sauna.

The Pre-Heat and Warm-Up Process

Outdoor saunas require time to reach optimal temperature. Pre-heating ensures an even, comfortable environment. Warm-up times vary by sauna design and insulation quality.

Warm-Up Times: Barrel Saunas vs. Insulated Cabin Saunas

Barrel saunas heat up quickly due to their compact shape. Insulated cabin saunas take longer but retain heat more effectively.

Typical warm-up times range from 30 to 60 minutes.

Temperature Ranges: Finding Your Personal Sweet Spot (70°C to 100°C)

Most users prefer temperatures between 70°C and 100°C. Comfort levels vary, so adjustments are often personal. Thermostats help maintain consistent heat throughout the session.

Two people relaxing inside a wooden sauna with benches and heater stones.

Post-Session Care: How the Sauna Resets

After each use, the sauna needs time to reset. Proper ventilation is essential once the session ends.

This protects both hygiene and structure.

The Drying Cycle: Preventing Mould and Mildew After the Steam

Leaving vents open after use allows moisture to escape. This drying cycle prevents mould and mildew from developing. It also keeps the interior fresh for the next session.

Maintaining Your Stones: When to Replace Crumbly Rocks

Sauna stones should be checked regularly. If they become crumbly or cracked, they should be replaced. This ensures safe heat storage and effective steam production.