Yacht Sauna Fails to Reach Set Temperature While Underway

It is very common for a sauna to function perfectly when the yacht is docked, yet fail to reach the set temperature while underway. This issue is almost always related to the electrical power supply, ventilation, or the stability of onboard systems. On this page we outline all the possible causes and provide practical solutions.
 

1. Voltage Drop from the Generator While Underway (Main Cause)

When the yacht is docked, the electrical system is powered by shore supply, which is usually stable. While underway, however, the sauna relies on the onboard generator, which may experience voltage fluctuations.

If the voltage drops (e.g. from 400 V to 360–370 V):

→ the effective power of the heater decreases
→ the heater produces less heat even if it continues to draw current

 

In these situations, the sauna may struggle to exceed 50–60°C (122–140°F) and may take significantly longer than normal to heat up. To resolve the issue, it is advisable to ensure the generator provides stable voltage, avoid running other high-power loads at the same time—such as air conditioning, stabilizers, or winches—and consider installing a dedicated regulator or stabilizer for the sauna circuit.

 

2. Heater Undersized for the Sauna Volume

While underway, external temperatures are often lower and airflow is higher. If the heater is already operating at its limit, it may struggle to reach the desired temperature. In practice, this means that the heater works just at its limit while docked, but struggles to exceed 60–70°C (140–158°F) while underway.

Technical guideline:
→ Approximately 0.75 kW per cubic meter of sauna volume
→ (up to 1–1.3 kW/m³ if there are glass panels or weak insulation)


3. Excessive Ventilation While Underway

While underway, onboard air circulation increases due to:

  • greater air exchange inside cabins
  • hull movement
  • pressure differences

This can excessively cool the sauna and cause it to “breathe” too much. It is therefore important to ensure that doors and vents are properly closed and that no airflow enters from air conditioning systems or extractors.

 

4. Temperature Sensor Reading Incorrectly

The temperature sensor may be affected by air currents, vibrations, or moving humidity inside the cabin. In such cases, it may display lower values than the actual temperature, causing the heater to compensate without effectively heating the sauna. To avoid this, the sensor should be installed approximately 160 cm (5 ft 3 in) from the floor, on the side opposite the heater, and away from direct airflow generated by yacht movement.

 

5. Stones Shifting Due to Vibrations

During navigation, the sauna stones may shift or compact, restricting airflow and reducing heating efficiency.

Consequences:

  • heater elements do not cool evenly
  • reduced heat output
  • significantly longer heating times

Solutions:

  • rearrange the stones to create proper air channels
  • replace broken or crumbling stones

 

6. Air Leaks from the Sauna Door

Even a 2–3 mm (0.08–0.12 in) gap during navigation can allow cold air to enter. The most common causes are:

  • door vibration
  • warped door frame
  • weakened magnetic seal

Under these conditions, the sauna struggles to exceed 60–70°C (140–158°F), making it difficult to reach the desired heat level.

 

7. Additional Electrical Loads While Underway

While the yacht is moving, several systems may be active and limit the power available to the sauna, including:

  • stabilizers
  • autopilot
  • onboard electronics
  • additional pumps
  • air conditioning operating in different modes

 

Typical Heating Times in Optimal Conditions

Under optimal conditions, a yacht sauna should reach 70–80°C (158–176°F) in approximately 30–45 minutes and 90–95°C (194–203°F) within 45–60 minutes. If heating times double while underway, the issue is most likely related to electrical supply instability or excessive ventilation.

 

When Is It Necessary to Call for Assistance?

If the sauna works correctly in port but struggles to reach temperature while underway, if the heater elements operate at half power, if the display shows sudden voltage fluctuations, or if a burning smell is noticed from the heater, it is advisable to contact professional assistance. To ensure proper operation and maximum safety of your onboard sauna, Centro Italia Yachting provides technical support and spare parts for all types of yacht saunas. You can contact the Italy Toll-Free Number 800 931 931 or from abroad +39 327 612 0605.