Usha Müller , 21.06.2021

Choosing the right air dehumidifier – buying tipps and advice

Experts recommend a relative humidity of 40% to 60% for a pleasant environment at home or work. If the room humidity is above 60%, the air is too damp and the room should be dehumidified as soon as possible. If the air humidity is too high for too long, mould can easily form and bad odours can be caused. Dark spots on the wall are an indication of mould formation. Water droplets (condensation) on walls, furniture and window frames can be a sign for excessive air humidity. An air dehumidifier helps to reduce the damp air in the room to an optimal level and prevent mould from forming indoors.

What does relative humidity mean?

Relative humidity is a measure of how saturated the air is with water vapour depending on the temperature. It is expressed as a percentage. The basic principle is: the warmer the temperature, the more water the air can hold. At a relative humidity of 100%, the air is fully saturated with water. When the air temperature drops, a situation occurs where the relative humidity exceeds  100% and the excess water condenses to form liquid water )condensation). This is called the “dew point temperature”. In the natural world, this is when mist or dew forms. In contrast to the relative humidity, the absolute air humidity is a measure of the water vapour content in the air (in grams per cubic metre). For human comfort, the relative humidity is more important than the absolute air humidity. The relative humidity not only depends on the water content in the air but also on the temperature of the air. Unfortunately humans can’t feel the air humidity precisely, therefore we use a hygrometer to measure air humidity.

Hygrometer Selina by Stadler Form

Causes of high air humidity

The following sources are the most common causes of high humidity in a room.

Lack of air exchange in new buildings

New builds tend to be very well insulated and have well sealed windows, however this unfortunately results in a lack of natural air exchange between the indoor and outdoor air. As new buildings are already inhabited shortly after completion, the building structure and materials often remain damp. A lack of air exchange can quickly lead to high humidity and a poor indoor climate.

Ventilating incorrectly or not often enough

If natural air exchange is lacking, regular and proper ventilation is very important for an optimal indoor climate. "Inrush airing", where opposite windows are opened fully for several minutes at least twice a day, is a particularly effective method. Particularly in summer, or if a property is not used much, lack of ventilation is often a cause of mould or bad odours.

Air dehumidifier against condensation on windows

Structural defects, poor insulation and the basement

Structural defects and an old or inadequate insulation can also be the cause of a poor indoor climate. If the indoor air is too humid in winter, it is possible that this moist and warm room air cools down on cold outer walls and condenses there, which can lead to mould formation. This usually happens in places that aren’t immediately visible, for example on a wall behind a cupboard. Basement compartments or laundry rooms are also very susceptible to excess humidity, as they are usually located below ground. The earth down there is often very moist and concrete cannot seal off the humidity – basements have a naturally damp environment. Other possible reasons for high indoor humidity can also be wet laundry, plants, showers and baths, fish tanks and terrariums, flooding, water damage or the property being located near a stretch of water.   

The causes of high room humidity are numerous and cannot always be clearly categorised. So what should you do if the hygrometer is showing a relative humidity of more than 60% and thus a poor indoor climate?

What to do if the indoor climate is too humid

Before buying an air dehumidifier, you should first of all try to eliminate or rectify any possible sources of humidity. For example, inspect water pipes or install an insulation against moisture on the basement exterior walls. Targeted and proper ventilation (inrush airing with dry outdoor air) of the room can also favour dehumidification. The use of a dehumidifier makes sense, if excess air humidity is measured over a longer period and sensitive materials need to be stored, or if mould starts to form on the walls and brick work. Existing mould must always be removed professionally, as the spores are harmful to health. If these measures aren’t enough to dehumidify a room, a dehumidifier can be an effective solution. Air dehumidifiers filter the excess humidity from the indoor air, thus preventing the formation of mould and the ensuing health risks.

How can an air dehumidifier help?

Air dehumidifiers can be used in lots of contexts. The air humidity is often a problem in old buildings. Draughty windows and a lack of thermal insulation can favour mould formation and a poor indoor climate. In addition to correctly heating and regularly ventilating a room with inrush airing, a dehumidifier can reduce the relative humidity to an optimal level. Use of a dehumidifier makes particular sense in rooms with a high amount of water vapour, e.g. in the bathroom and kitchen. This helps not only to combat the high air humidity levels seen in bathrooms, but also to prevent silverfish, which thrive best in dark, damp rooms. Dehumidifiers also find their place in the car, where the device is used so that the windows do not fog up and to prevent mould from forming on upholstery and fittings. Dehumidifiers are also used to dry laundry in the home if the property does not have a laundry room or clothes dryer, or if the laundry needs to dry gently. A laundry dehumidifier lets textiles dry more quickly and at the same time creates an ideal indoor climate. The dehumidifier can also clean the room air. The condensed water binds to particles of dirt and fine dust and washes them out in the water tank. Some models have integrated heating, making the drying process even quicker. In the case of water damage, a dehumidifier can be a cost-efficient, effective and useful solution to reduce air humidity. It is important to start using it straight away, before the damp gets into the plaster and brick work. Professional use of a dehumidifier therefore makes particular sense in the case of water damage. Air dehumidifiers used for drying buildings or cleaning-up major water damage are called building dryers. They are robust machines and have a higher dehumidification capacity than standard air dryers for private use.

Dehumidifying a laundry room

How does an air dehumidifier work?

Air dehumidifiers work by means of two different processes – condensation and adsorption – which are explained in more detail below.

Condensation takes place when the air cools and liquid water is formed. The moist room air is sucked in by a ventilator and cooled by a heat pump condenser, condensing the water in the air into liquid form. Then the dry air is heated again by the heat pump condenser and released back out into the room. There it continuously mixes with the moist room air, until the target air humidity is reached. The water released from the air is either collected in a water tank or the water is drained to an outlet through a water hose. However, this method can lead to the condenser icing up. Therefore, when buying an air dehumidifier, you should check that the appliance has a defrosting sensor or frost protection (defrost feature). Nowadays, nearly all modern dehumidifiers have a defrost feature. Many dehumidifiers are equipped with a hygrostat. Thanks to the hygrostat the devices are very energy-efficient as they switch off automatically as soon as the desired humidity is reached.

Dehumidifier Albert by Stadler Form detail view condensation

The other process is that of adsorption drying. Adsorption is the concentration of gases or dissolved substances on the surface of solid objects. Desiccant is still often used for this. The water vapour is adsorbed by the desiccant and thereby removed from the air. However, dehumidification using a desiccant dehumidifier is not an optimal alternative compared to electric air dehumidifiers with hot air regeneration, because the dehumidification performance is rather low.

What should you consider when buying an air dehumidifier?

Buying an air dehumidifier is not an easy task and should be thought through carefully. There are many different criteria to consider to avoid unnecessary costs. Below, we take a look at the most important criteria that should be considered when buying an air dryer.

Room size: The room size is a crucial factor in choosing the right air dehumidifier. Large rooms naturally require a high dehumidification capacity. The room volume should be considered here and not the surface area (area in m2 x room height). As a general rule, manufacturers assume a room height of 2.5 metres for their room size recommendations.

Purpose of use: You should think carefully about where the air dehumidifier is to be used (e.g. laundry room, basement, living room or bedroom). Depending on which room the dehumidifier is to be used in and what the required capacity is, other criteria are also important. This is why there are various models differing in design and purpose of use. For example, if dehumidification of wet laundry is required, an oscillating air dehumidifier (also known as swing mode) would be a good option. This feature ensures optimal air distribution in the room. For water damage however, an industrial building dryer would be required. Or, for dehumidification of living spaces, such as bedrooms or living rooms, a quiet dehumidifier with night mode would be ideal. A portable air dryer is beneficial for dehumidifying a number of rooms, as this can be moved from one place to another on wheels.

Dehumidifier Theo in the bathroom by Stadler Form

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Technology: Depending on the purpose of use, different integrated technologies can be important. In the bedroom, for example,  you don’t want the LED indicator lights to be bright. Therefore, the LEDs should be dimmable or the appliance should have a night mode. In a small room, it’s important that it isn’t over-dehumidified. Therefore, you should choose an air dehumidifier with an integrated hygrostat. As soon as the target humidity is reached, the device automatically switches off. The timer feature is also an important criterion. Dehumidifiers with a timer mean you can choose when it switches on and off, allowing you to take advantage of cheaper energy tariffs, for example. In addition, the air dryer should be fitted with an automatic shut-off, so that it switches off independently when the water tank is full.

Energy consumption: With very high air humidity, the dehumidifier should  run continuously if possible. However, the energy consumption can nevertheless be controlled. It is important that the dehumidifier has a hygrostat. This can be used to set the desired target air humidity. Once the target air humidity is reached, the appliance automatically switches off.

Water tank capacity: Depending on the model and purpose of use, the water collecting capacity is also very important. Standard air dehumidifiers for private use mostly have a maximum dehumidification capacity of 30 liters per 24 hours and a maximum water tank capacity of 8 liters. The air dehumidifier will ideally have a connection point for a hose to drain the condensed water directly.

Price: Desiccate dehumidifiers are relatively cheap to buy. However, the ongoing purchase of desiccate should be taken into account in the overall cost. In the case of compressor dehumidifiers, quality comes at a price. For a dehumidifier to work reliably over a number of years, it needs to be built with quality components. These components are reflected in the price.

Do you want to learn more about dehumidifier appliances from Stadler Form? When buying an air dehumidifier it is worth getting acquainted with the facts first and getting professional advice. Contact us here. Air dehumidifiers from Stadler Form, such as Albert or Theo, are efficient to run and leave you with dry rooms, a healthy indoor climate, and improved well-being. Further information on air dehumidifiers can be found on the Stadler Form product page under Air Dehumidifiers. Or visit our Online Shop to find the right product for you.

Air dehumidifier Albert and Albert little by Stadler Form

Click on the following link to watch a short video on the air dehumidifier Albert from Stadler Form.


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