Damp walls, steamed-up mirrors and a musty smell – who doesn’t know the feeling? What may seem like a minor nuisance at first glance is, in reality, a serious problem that quietly takes hold within the walls of your home. Damp cellars and poorly ventilated bathrooms are among the most common causes of mould growth in Swiss households. Once relative humidity remains above 65 per cent for a prolonged period, mould spores can begin to grow within just a few days, potentially causing lasting damage to masonry, timber structures and the health of the occupants. In many cases, a dehumidifier is the most effective and affordable immediate solution before extensive drying works or costly waterproofing measures become necessary. However, it is crucial to use these devices correctly – because a poorly positioned or undersized dehumidifier does not solve the problem and, at best, merely conceals it.
Where does the moisture actually come from?
Before considering the correct use of a dehumidifier, it is worth taking a closer look at the causes. Sources of moisture can be divided into three main categories, which often occur at the same time and reinforce one another.
Condensation moisture occurs when warm, humid air comes into contact with cool surfaces. This typically happens in summer, when outside air at 20°C and 80% relative humidity enters a cool cellar and condenses there. Many homeowners open their cellar windows in summer because they believe they are ventilating the space properly – yet this well-intentioned measure often makes cellar dampness considerably worse. Warm summer air carries more absolute moisture than the cool cellar air is able to absorb.
Capillary moisture refers to groundwater or soil moisture rising through the masonry. This problem occurs particularly in houses without a functioning damp-proof course and can rarely be resolved permanently without structural measures. In such cases, a dehumidifier can alleviate the symptoms, but it cannot replace professional waterproofing.
Occupancy moisture is the third and often underestimated source: a household of four can produce up to 12 litres of water vapour per day simply through showering, cooking and breathing. A significant proportion of this remains in the bathroom or cellar if adequate ventilation is not provided.
The Bathroom: A Small Room with a Heavy Moisture Load
Das Badezimmer ist der Raum mit der höchsten Feuchtigkeitsbelastung im gesamten Haus. Besonders in fensterlosen Badezimmern oder bei unzureichender mechanischer Lüftung staut sich die Nässe nach jedem Dusch- oder Badevorgang. Die relative Luftfeuchtigkeit kann dabei innerhalb von Minuten auf über 90 % ansteigen – Werte, bei denen Schimmelsporen sofort zu keimen beginnen.
Always run a dehumidifier after showering or bathing, especially if there is no window. Moisture settles on cold tiles and mirrors and provides the ideal breeding ground for mould. Joints between tiles and sanitary fixtures are chronic weak points: if the grout loosens due to constant moisture exposure, water penetrates behind it—and the damage only becomes visible once the tiles have already been undermined.
The health consequences should not be underestimated. Cladosporium, Aspergillus and Stachybotrys are the most common types of mould found in damp bathrooms. Their mycotoxins can trigger respiratory illnesses, allergic reactions and, with chronic exposure, even serious diseases. For people with asthma or a weakened immune system, mould in the bathroom poses a particularly serious risk.
Which device is suitable for the bathroom?
For the bathroom, a compact, powerful unit is recommended—one that responds quickly and rapidly reduces humidity to a safe level after showering. The DH12 is an example of a unit designed for bathrooms of all sizes. It efficiently removes excess moisture from the air, protecting both the building fabric and occupants’ health. It’s important that the unit runs during use of the bathroom and for up to 30 minutes afterwards, so the moisture produced is removed immediately.
There are also special safety rules in the bathroom: the dehumidifier must not be placed directly in the splash zone (protection zones 1 and 2 according to DIN VDE 0100-701), but must be positioned at least 60 cm from the edge of the shower or bathtub . At the same time, it must be placed close enough to where the moisture is generated.
The basement: a microclimate with its own rules
The basement is a room with its own distinct microclimate. While the bathroom is exposed to short-term, intense humidity spikes, the basement often struggles with a permanently elevated baseline humidity. Depending on the size and moisture level of the basement, the continuous presence of a dehumidifier that constantly monitors relative humidity is strongly recommended. This is an essential preventive measure against mould and, in the long run, far cheaper than later remediation.
The financial consequences of mould damage are clearly calculable—and alarmingly high: professional mould remediation in a basement costs between €1,500 and €8,000, depending on the extent of the infestation. Replacing screed and insulation after water saturation can cost €5,000 to €15,000. On top of that, proven mould infestation can reduce a property’s value by up to 15% of its market value . Investing in a good dehumidifier therefore pays for itself after just a few years.
Choosing the right type of unit for the basement
Not every dehumidifier is equally suitable for a basement. Choosing the right type of unit depends crucially on the temperature in the basement.
Unit type | Operating principle | Optimal temperature range | Recommended for |
Condensation dehumidifier | Cools air below the dew point; water condenses | From approx. 15°C | Heated basements, laundry rooms |
Desiccant dehumidifier | Binds moisture to a desiccant (silica gel) | Even below 10°C | Unheated basements, garages |
Condensation dehumidifiers work on the same principle as an air conditioner: they cool the room air below the dew point, the water condenses and is collected in a tank. They are energy-efficient and powerful, but lose effectiveness significantly at temperatures below 15°C—sometimes by up to 40% of their dehumidification capacity .
Desiccant dehumidifiers, on the other hand, bind moisture chemically to a desiccant (usually silica gel) and are therefore independent of outdoor temperature. They are the first choice for unheated basements where the temperature drops below 10°C in winter.
Correct placement: the decisive factor
Even the most expensive dehumidifier is of little use if it’s positioned incorrectly. Placement largely determines whether a unit uses 60% or 90% of its technical capacity—a difference that directly affects electricity costs and drying speed .
Dehumidifiers work on the condensation principle: room air is drawn in, passed over a cooling coil, the condensate is collected, and dry air is blown back out. For this cycle to work optimally, the unit needs at least 30–50 cm of clearance on all sides—especially from the wall behind the air outlet. If you place the unit directly in a corner or in front of a cabinet, you may end up recirculating air that has already been dehumidified, unnecessarily extending the operating time.
The ideal position in a basement is the geometric centre of the room, or at least a central spot with unobstructed airflow from all sides. In long, narrow basement rooms from around 6 m in length, placement in the middle third is recommended rather than at one of the ends . This allows the unit to reach damper wall areas that would otherwise be in a dead zone.
Another important aspect: because humid air is heavier than dry air, it collects near the floor. A unit that draws air in just above the floor captures the most concentrated layer of moisture first. Critical moisture sources—such as leaking basement walls, washing machines or laundry drying areas—should be within the intake fan’s capture zone, not in the outlet area.
Practical tips for optimal operation
To ensure your dehumidifier can deliver its full performance, keep the following points in mind:
Keep all doors and windows closed during operation. Open doors effectively increase the room volume and overload the unit, as it then also has to combat moisture from adjacent rooms. If possible, use a drain hose instead of manually emptying the water tank. A full tank stops the unit automatically—and in a damp basement it can fill up faster than you might think. Never place the unit directly in front of exterior walls, as condensation on the wall can force the unit into a continuous cycle.
When is a dehumidifier the right solution?
A dehumidifier is a preventive measure against mould, not a cure-all. It treats the symptoms, not the cause. If the moisture is caused by structural defects such as missing waterproofing or faulty pipes, the cause must be fixed first. A dehumidifier is then the ideal addition to stabilise the indoor climate in the long term.
As a rule of thumb: if the relative humidity in your basement or bathroom is consistently above 60% and you cannot identify any structural defects, a dehumidifier is the right and cost-effective solution. A simple hygrometer for just a few francs provides the key measurement and helps you control the unit’s operation optimally .
Invest in a suitable unit, position it correctly, and protect your home, your health and your property value for the long term. Because mould prevention is always cheaper than mould remediation.
