Ventilating your cellar properly: Put an end to damp and mould
Cellars place high demands on adequate ventilation. They are often damp, smell musty and provide the ideal conditions for mould growth. In cellars with little or no insulation in particular, constantly high humidity causes the walls to become damp. With the right ventilation, you can ensure an optimal cellar climate. That is why effective humidity-controlled cellar ventilation is needed to ensure an optimal cellar climate.
Why traditional window ventilation in cellars is often harmful
The danger of summer condensation
Ventilating a cellar has its own set of rules: Since cellar walls are usually cooler than the outside air, there is a risk of what is known as summer condensation. Warm air enters, cools down, and condenses on your walls - creating the perfect breeding ground for mold.
The problem
Warm outside air contains a lot of moisture. When it comes into contact with cool walls in the cellar, it cools down and can no longer hold onto the water.
The result
Moisture condenses on the walls is the ideal breeding ground for mold growth.
The rule of thumb
Ventilate only when the outside air is colder and drier than the inside air to ensure building protection.
The following matrix clearly shows that effective dehumidification is a physical interaction between temperature and relative humidity. To keep your cellar permanently dry, ventilation should therefore not be based on intuition, but rather be data-driven . Our smart sensors handle this balancing act for you and only let fresh air in when it actually dries out your cellar.
| Weather Conditions | Physical Effect | Recommendation / Risk |
|---|---|---|
| Winter (Cold & Dry) |
Cold outside air warms up in the cellar and can thus absorb a massive amount of moisture. | Safe Ideal: Maximum dehumidification of the walls possible. |
| Summer (Warm & Humid) |
Warm air cools down on cold walls. The moisture “condenses” (condensate). | Danger Stop: Close the windows! Risk of mold due to moisture ingress. |
| Thunderstorm/Rain | The outside air is saturated with moisture. Ventilation has the opposite effect. | Danger Stop: The cellar will get damp immediately. |
| Summer Night | Cooling reduces absolute humidity. Only possible with cool night air. | Conditional Note: Only safe with dew point control. |
Smarter than physics allows: LUNOS cellar protection
Forget complicated outdoor sensors and error-prone calculations. We’ve put the intelligence where it belongs: right in the fan.
The risks of conventional cellar ventilation systems with dew point control
Many systems rely solely on dew point control. The key drawback: This only reacts once moisture has physically condensed - meaning the walls are already “wet.” However, structural damage occurs much earlier, as mold begins to grow at humidity levels as low as 80% - long before the temperature even drops below the dew point. While older systems still give the “green light,” the danger to the building structure has long since become a reality.
Conventional cellar ventilation systems often rely solely on dew point control. But for true building protection, this usually comes too late.
A dew point control system only reacts once moisture has physically condensed - that is, once things have already become “wet.” The problem: Mold begins to grow at humidity levels as low as 80%, long before the temperature drops below the dew point. Structural damage therefore occurs even while the dew point control system is still giving the “green light.”
The smart alternative from LUNOS
Instead of relying on sluggish outdoor sensors, our cellar ventilators feature built-in mini-computers. These continuously analyze the microclimate directly within the unit to prevent mold growth before it can occur. But what makes this system so unique? The following four core features ensure fully automatic and highly efficient building protection without manual intervention:
Our controllers do not require error-prone external sensors. They detect all relevant parameters directly at the fan.
Even when the fan is not actively ventilating, it briefly circulates the air to collect highly accurate measurement data from inside the room.
The system continuously generates ventilation profiles. It immediately determines whether ventilation is advisable or whether humid outside air would exacerbate the problem.
The system runs quietly in the background. It automatically reduces power consumption and uses optimal time slots for dehumidification.
Solutions for every cellar requirement
From functional utility cellars to cosy cellar living spaces: our systems actively protect your building structure against mould and damp. Whilst the Silvento ec with cellar board acts as a self-contained exhaust air solution to stop moisture ingress from outside, the e² and ego offer highly efficient ventilation with heat recovery – ideal for inhabited cellar rooms, hobby areas or utility rooms. Discover the right components for your project here:
Fully automatic mould protection in combination with the cellar board.
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When used in conjunction with the cellar board, it determines the ideal time for ventilation.
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For the Silvento: Monitors the absolute humidity in the cellar.
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For utility rooms and basement bathrooms: just one wall-mounted unit with heat recovery.
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For basement living spaces: Provides effective protection against mould and helps retain heat in the room.
Details →Is your cellar ready for summer? Take the test!
Do you feel that your cellar is too damp, or do you want to take proactive steps to prevent mould? Our interactive quiz analyses your current situation in less than two minutes. Get an instant assessment of whether your cellar is adequately protected or whether action is needed to maintain the value of your property.
Check: Is your cellar in good shape?
If you answer ‘yes’ to more than two questions, an automated ventilation solution is highly recommended to maintain the value of your property.
Protect your property from damp in the long term. Our experts will be happy to advise you on the right retrofit solutions for your property or put you in touch with a local specialist.
FAQ: Questions about ventilating cellar rooms
This is due to what is known as summer condensation. When warm, humid outside air enters the cooler cellar in summer, it cools down on the walls. As cold air can hold less moisture, the excess water condenses on the walls – creating the ideal breeding ground for mould. Manual ventilation in summer therefore often makes the problem worse rather than solving it.
The most effective solution is an automated ventilation control system that constantly compares the humidity levels indoors and outdoors. Only when the outside air is actually drier (lower absolute humidity) is the ventilation process activated. Systems such as the Silvento ec with a specialised basement circuit board ensure that moisture is actively removed without bringing in new moisture from outside.
Relative humidity depends on temperature (e.g. 60% at 25°C). Absolute humidity indicates the actual amount of water in grams per cubic metre of air. For the basement, only the absolute value is decisive: the ventilation system can only dehumidify the basement if there are fewer grams of water in the air outside than inside. Our intelligent control systems calculate this difference fully automatically.
A dew point control system uses sensors in the basement and outdoors. An algorithm calculates the dew point based on temperature and humidity. The fan (e.g. Silvento ec) only switches on when the physical conditions allow for dehumidification. This prevents humid air from flowing in on warm days and condensing on the cold cellar walls.
Heat recovery (e.g. via the e² series or the ego) is ideal for basements used as living spaces, home offices or hobby rooms. These systems keep the heat inside the building whilst continuously supplying fresh, filtered air. This saves on heating costs, protects against mould and ensures a comfortable indoor climate, just like on the upper floors.
Yes, decentralised ventilation systems are ideal for renovation. No complex ductwork is required; a simple core drill hole in the external wall and a power connection are all that is needed. Systems such as the ego require just a single hole to provide both supply and extract air with heat recovery.
Yes, continuous ventilation is an effective way of reducing radon levels in cellars. Regular air exchange ensures that the radioactive noble gas escaping from the ground is vented outside before it can build up to concentrations that pose a health risk.
Thanks to modern EC motor technology, running costs are extremely low. On average, a basement fan often uses less electricity than a modern LED light. The savings achieved by protecting the building structure and avoiding costly mould remediation far outweigh the low electricity costs.