Dehumidifier to dehumidify the basement

Damp cellars are not only a problem in old walls. Even in insulated new buildings, the relative humidity can quickly exceed the ideal 40-60%. This damages the items stowed in the basement and leads to mold in the long term. With a room dehumidifier you can get the problem under control.

It smells musty, the plaster is peeling off the wall, stowed cardboard boxes and fabrics feel clammy or even wet. These are all typical signs of excessive humidity in the basement. Sooner or later, such a room climate creates mold – and this is not only extremely unhealthy, but also affects the stowed utensils. When that happens, the only thing left to do is muck out. But it doesn’t have to come to that.

How does moisture develop in the basement, which dehumidifiers are recommended and are there other ways to solve the problem? You can find answers in this post.

Too much moisture in the basement: a problem especially in the mild season

In uninsulated old buildings, moisture penetrates the walls from the outside. But even in well-insulated houses and previously dry cellars, the unpleasant wetness often occurs at some point. The culprit is called condensation moisture, which forms on cold surfaces.

The formation of condensation water can take place on all surfaces, for example walls, furniture and especially window panes. It depends on various factors:

  • Outside temperature
  • Temperature in the room
  • Surface temperature
  • relative humidity

The higher the humidity in the room and the colder the surfaces, the stronger the condensation. Furthermore, the temperatures outside and in the room play an important role, as warm air can absorb more water vapor than cold air.

For this reason, the formation of condensation moisture in the basement is a problem, especially in the warm spring and summer months. At this time, warm outside air gets into the year-round cold basement rooms and cools down accordingly. The now cold air can no longer absorb as much moisture as before. As a result, the excess moisture condenses on the cold walls in the basement.

In this case, ventilation is not the best choice!

Ventilation only helps when the outside temperature is appropriate!

Most people first try to combat damp basements with intensive ventilation. What seems plausible at first is in reality often exactly the wrong path – for the reasons mentioned above. In spring and summer you should keep the windows in the basement closed as much as possible to let the warm (humid) air outside.

Ventilation of your cellar is only recommended if the temperature outside is at least five degrees below the cellar temperature. Of course, that hardly ever happens in summer. You should therefore use autumn and winter to ventilate your basement rooms regularly – but only on dry days, please!

Of course, this requires meticulous monitoring of the temperature and increases heating costs. In addition, it doesn’t really help in summer.

Dehumidify basement

For year-round ideal humidity, it might make sense to purchase a dehumidifier to dehumidify the basement. These electrical devices suck in the air via a fan function, cool it and collect the resulting condensation in an integrated water tank.

There are also dehumidifiers that work without electricity. These are cushions or containers filled with water-absorbing substances, for example salt crystals, siccatives or activated carbon. Since the fan function is missing, the efficiency is lower here than with the electric version. However, this measure may already be sufficient.

The simplest cause: a leaking water pipe

If no wall has to be pried open to seal the leaking pipe, this problem can usually be remedied quickly and inexpensively. With other causes, the situation is usually more complex.

Cause: lack of horizontal sealing

If the basement walls are damp, the reason, especially in the case of older buildings, can be a lack of horizontal sealing to the ground. This can be drawn in later, for example by slitting open the masonry inside or outside and inserting sheet metal.

Cause: missing or overloaded drainage

If water penetrates through the light shafts of basement windows when the groundwater level is high, or if seepage water collects on hillside properties and intensive precipitation does not flow off, the reason could be missing or overburdened drainage. To ensure that they function optimally over the long term, TÜV experts recommend having the drains serviced and flushed by a specialist every ten years.

Cause: incorrect ventilation

Basements should never be ventilated during the day when the outside temperature is high. Because warm air stores significantly more moisture than cold air. And if the air in the basement cools down in the evening, the moisture condenses on the equally cool wall.

Cause: defective protective coating

There is also a risk of moisture penetration vertically due to defective protective coatings. Bitumen, for example, the waterproofing for the basement tub, decomposes after around 30 to 40 years. Replacing the waterproofing is usually very costly, because the outer walls around the house have to be dug down to the bottom and re-sealed.

Cause: blocked roof drain

If a damp spot keeps showing up in a basement corner, the cause here could be a clogged roof drainage system on the house wall: Drained rainwater accumulates in the gutter and at some point pushes through the wall. That is why gutters and downpipes should be kept free at all times. If damp spots have already formed on the walls, the use of a construction dryer should be checked in order to avoid consequential damage.

Tips for ventilation in the basement:

  • Never ventilate the basement during the day in summer! Ventilate only on cool nights and mornings
  • Autumn and winter are suitable for ventilating the cellar
  • But be careful: ventilate the room instead of tilting the window!
  • Do not dry laundry in the basement (exception: if a powerful dehumidifier is used!)

Damp walls? Dehumidifier for the basement? Make the right choice!

Dehumidifiers are helpful when there is no structural damage, but the moisture is caused by condensation. If tiles, basement walls are wet and damp – especially in summer – this indicates condensation. A dehumidifier works both preventively and in acute situations to reduce the humidity in the basement air and protect the building fabric.

When choosing the best dehumidifier, there are a few factors to consider :
The performance of the dehumidifier must be efficient – not just at high temperatures!
Much more important is the performance the device achieves at typical cellar temperatures! Many conventional household condensation dryers have a very poor power consumption-to-performance ratio at low temperatures. The power consumption of these dehumidifiers is comparatively high. Electricity costs of several hundred euros are not uncommon with these devices …

When making your selection, make sure that the dehumidifier has the function of an automatic control that is designed for basement temperatures – for example an iECO control. This also ensures drying in the basement temperature range. With devices of the regenerative dryer series even at + 2 ° C!

Efficient dehumidifiers should also have a powerful fan installed in order to optimally distribute the room air. This is the only way to dry the dry air evenly and effectively.

In order to choose the right model of the basement dehumidifier, the following factors must be taken into account:

  • Height of the room
  • Room volume
  • Room temperature
  • Humidity of the basement rooms

Would you like information on the acquisition costs for dehumidifiers? Please send us your questions – we will be happy to assist you in selecting a dryer!

how does dehumidifier work

Dehumidifier basement –
how it works

There are two basic types of dehumidifiers: condensation and adsorption dryers.

In principle, condensation dryers are reminiscent of the well-known refrigerator system. 

The water droplets produced during the condensation process are caught in a container – or fed directly into the sewer.

Adsorption dryers dehumidify the ambient air with the help of a desiccant. The absorbed moisture is then conducted outside through an air hose. 

Because of their high energy consumption, adsorption dryers are rarely used in the private sector.

Electricity – watt – dehumidifier

The device performance is given in watts. It should be noted that the nominal power should never be equated with the actual power consumption. 

The actual power consumption of the device is strongly influenced by the room temperature . The lower the temperature, the lower the energy required. However, the lower the dehumidification performance!

Conversely, the higher the ambient temperature, the greater the energy consumption, but also the greater the dehumidification performance. The energy consumption can only be determined in continuous operation. It is therefore crucial that manufacturer comparisons are not made based on the “maximum consumption” – ideally, power consumption is given at different temperature ranges.

It is crucial that the performance of dehumidifiers is not only given at 30 ° C – but above all at 20 ° C. This allows the different dehumidifier models to be compared at practical temperatures. Values ​​at 30 ° C are completely irrelevant – because we don’t have such high cellar temperatures in Central and Western Europe!

A note on the volume: When operating a dehumidifier in the basement, the noise level plays a subordinate role in contrast to the living space. Much more important for the dehumidification in the basement are the fan performance and the energy costs!

By the way: The water tank of the dehumidifier should be at least 8 liters (preferably 10 to 15 L in size). If there is a floor drain, a hose connection on the device is helpful in order to be able to directly drain off the condensation water. 

Dry basement thanks to the best dehumidifier performance

What fan output should a dehumidifier for the basement have?

The basement dehumidifier should have a fan capacity of at least 300 to 500 m3. Make sure, however, whether the device specification is free-blowing (fan without housing / resistor) or – “Measured on the front grille” – is given.


The lower the air output, the lower the air distribution.

The lower the air distribution, the smaller the dryable area.

If a dehumidifier with 150 m3 / circulation capacity includes a drive unit with an impressive 500 watts of power – what is the use? In the absence of ventilation, the dehumidifier is already 5 meters away, and dry air can hardly be felt. Ergo, a moisture reduction over a larger area is not possible. Despite high consumption….

Professional cellar dehumidifiers have a fan output of 500 m3 / h (free blowing). This corresponds to a practical output of around 300 m3 / h.

A sufficiently large water tank is recommended.

In addition to the fan output , the power consumption is the second selection criterion for a basement humidifier:
This value is more important than the purchase price ! Why? Because – especially in the case of devices produced in the Far East (sometimes with very German-sounding names …) – the relation of ACTUAL dehumidifier performance to ACTUAL consumption very often shows a massive disproportion.

The electricity costs of these cellar dehumidifiers can even exceed the purchase price of a high-priced dehumidifier in a few years. A dehumidifier that is expensive to purchase – but equipped with iECO control – can save several hundred euros in 5 years! A basement dehumidifier designed in this way “pays for” its acquisition costs by itself!

How loud is a dehumidifier – is the noise level significant?

The volume depends on the respective dehumidifier model. Bedroom dehumidifiers should not have more than 45 dB (A). In the case of cellar dehumidifiers, the noise level should be set at a moderate level – because a cellar is separated from the living area by a solid false ceiling that isolates the sound. Noise nuisance would only exist if the ceiling is not sufficiently soundproofed and the dehumidifier has over 60 dB (A). But that would only be the case with industrial devices.
Basement dehumidifiers require a medium to high fan output – and powerful fans cannot be “whisper-quiet”. There are, however, models whose fan blades are designed according to the “owl blade concept” – that is, despite their high performance, they score with a relatively moderate noise level. Devices of the WD-S class, for example, are equipped with this technology.

Basement dehumidifiers of the optimal performance class usually show between 40 and 58 dB (A) in practice. If the basement is used in a homely manner, you should deactivate the dryer if you are particularly sensitive to noise – and the dehumidifier will be switched on after leaving the room.

How To Choose the Right Size Dehumidifier

If you need to buy a portable dehumidifier, the first question you should ask yourself is “What size dehumidifier do I need?” Answering this question is simple—if you have the right information.

Read on to learn how to choose the right size dehumidifier for your needs.

How Dehumidifiers Are Sized

A dehumidifier’s size is determined by its total moisture removal capacity. Capacity is rated in pints of moisture removed per day (24-hour period).

A dehumidifier’s capacity loosely indicates how large of a space it will cover in square feet. Therefore, if you know the square footage of the area you’d like to dehumidify, you can get a good idea of the capacity you will need. 

For example, when you see a “30-pint dehumidifier,” you’re looking at a model that’s rated to remove 30 pints of moisture total per day at testing conditions. The updated testing conditions are 65 degrees F and 60% humidity. Previously, dehumidifiers were tested under 60 degrees F and 80% humidity, but those testing standards were updated in 2020 to reflect more real-world conditions. 

Dehumidifier Sizing Chart

To help simplify your search even further, we’ve created a handy dehumidifier sizing chart. This chart will help you choose the right size dehumidifier.

Note: Dehumidifier testing standards changed in 2020. Dehumidifiers are now tested in colder temperatures, which lowers their total pint capacities compared to older models.

You’ll notice the updates reflected in our chart below: 

review how old pint capacities compare to new capacities under new dehumidifier testing standards

Room Size vs. Room Conditions

Choosing a dehumidifier based on the size of your space and its capacity alone isn’t enough. To find the absolute best solution, you’ll also need to consider your room’s conditions.

Start by asking yourself, “How damp is my space?” If it’s only a little damp, you can probably stick with the rated capacity for your square footage. If you’re dealing with an extremely wet space, you’ll definitely need a large capacity unit.

For example, a model that removes 50 pints of water when the air is saturated is less powerful than a model able to remove 50 pints of water at standard room conditions (65 degrees F, 60% humidity).

Find the Right Dehumidifier

Once you know which size dehumidifier you need, it’s time to find yours.

Additional Room Conditions to Consider

If any of the below factors are true for you, you’ll want to choose a unit with a higher capacity.

  • If your home is located in a humid climate, add 10 pints.
  • If multiple people live or will spend time in the space, add 5 pints.
  • If there are multiple doors and windows in the space, add 5 pints.
  • If there’s a washer and dryer nearby, add 5 pints.

In Summary

Look at pint capacity and the dampness of your space to choose the right size dehumidifier for you. Our chart will help.

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