Last updated: August 10, 2021

Hygrometers are very practical devices. You can use them to reduce the risk of mould growth in your home. This is very important because mould is unhealthy and can cause health problems. You can also use a hygrometer to control humidity in humidors, terrariums and garden sheds.

In all these areas, it is important to keep the humidity in the optimal range. To help you find the right hygrometer, we have listed the advantages and disadvantages of various hygrometers in our hygrometer test 2021. In addition, we have described what alternatives there are to measure the air humidity.




Summary

  • If you have problems with mould in your flat or house, you should get a hygrometer. It is also important to check the humidity in garden sheds or terrariums.
  • There are many different types of hygrometers, so you are sure to find one that suits your needs. Depending on the functions you want your hygrometer to have, there are either cheaper or more expensive models.
  • To keep your hygrometer accurate, you need to calibrate it regularly. There are several ways to calibrate a hygrometer.

The Best Hygrometer: Our Choices

Guide: Questions you should ask yourself before buying a hygrometer

What is a hygrometer?

A hygrometer is a device with which you can measure the humidity of the air. Basically, you have to distinguish between relative and absolute humidity. Absolute humidity is the actual amount of water vapour in the air. However, air can absorb more water when it is warmer, which is then the relative humidity.

It makes sense to keep an eye on the humidity in order to avoid mould growth.

Therefore, it is advisable to place a hygrometer in rooms that are prone to mould. Now you can find out why which rooms are susceptible to mould:

  • Bathroom: Showering can quickly cause the humidity to become too high.
  • Kitchen: Cooking involves more water, which can create a lot of water vapour.
  • Cellar: Cellars are often not well heated because they are not really used. This, however, favours mould growth.
  • Laundry rooms: Rooms where clothes hangers are placed are also at risk. This is because the humidity in the room increases due to the wet laundry.

The optimal humidity is between 40 and 60%. At relative humidity levels below 40%, the air is very dry and many people find it quite uncomfortable. At values above 60%, the risk of mould is very high.

Humidity Air
Below 40% Dry
40-60% Optimal
Above 60% Humid

To counteract air that is too dry or too humid, you must ventilate or heat the room regularly. It is also important to measure the humidity for the correct storage of cigars in humidors. The same applies to terrariums, because some animals run the risk of becoming ill if the humidity is too low.

How much do hygrometers cost?

The prices of hygrometers vary greatly, depending on the hygrometer's features. There are hygrometers for less than 10€, but these are usually rather inaccurate.
Most hygrometers cost between €20 and €40.

Accurate hygrometers start at around 20€. But there are also some that cost over 100€. More expensive hygrometers are more accurate than the cheaper ones. Many hygrometers in the higher price range are also equipped with additional functions, such as a mould alarm.

What types of hygrometers are there?

There are different types of hygrometers, which in turn use different measuring methods. Here we have described the most common types of hygrometers:

  • Absorption hygrometers: Absorption hygrometers are based on a hygroscopic (water-attracting) material whose properties change due to the air humidity. The hair hygrometer belongs to this group. The hair hygrometer contains a hair that expands when exposed to moisture. In the past, women's or horse hair was used, but today synthetic hair is used. The change in the hair is transferred to a pointer, which then indicates the relative humidity on a scale. In order to display accurate values, you have to readjust this hygrometer every 4-6 months.
  • Psychrometer: The measuring principle of psychrometers is very accurate, which is why it is used in many weather stations. Psychrometers consist of two thermometers. One of the thermometers is wrapped in moist material. Because heat is extracted from the wet thermometer by evaporation, it shows a lower temperature than the dry thermometer. The temperature difference between the two thermometers is a measure of the relative humidity. The lower the difference between the temperatures, the more humid it is.
  • Dew point hygrometer: The dew point mirror hygrometer measurement method is considered the most accurate method. It uses a mirror that is cooled down until the humidity condenses on it. A photosensor and a light source are then used to determine the moment of condensation. To convert the dew point into absolute humidity, you need the air pressure at the time of measurement. For relative humidity you also need the sample temperature.
  • Chemical hygrometer: Changes in the material due to chemical reaction with water are measured by chemical hygrometers. This would be, for example, colour changes that are displayed on a test strip.
  • Optical hygrometers: The absorption of light is measured with a wavelength typical for water vapour or by the change in the refractive index. These measurements are used to determine the humidity of the air.

What are the alternatives to hygrometers?

There are also ways to measure humidity without a hygrometer. We will now explain how this is possible:

  • Apps: If the necessary sensors are built into your mobile phone, you can use an app to determine the air humidity via your mobile phone. These sensors are used by the app to measure the relative humidity at your location.
  • Moisture meter: With this device you can measure the water content of material surfaces such as concrete or wood. Basically, moisture meters work much like hygrometers, except they don't measure continuously, only at the touch of a button. They are also more expensive than hygrometers.

Decision section: What types of hygrometers are there and which one is right for you?

If you want to buy a hygrometer, there are two different types to choose between:

  • analogue hygrometers
  • digital hygrometers

Both types have advantages and disadvantages, which we will explain to you. In the following part, we want to help you make a decision.

What are the features of an analogue hygrometer and what are its advantages and disadvantages?

Analogue hygrometers can work mechanically without electricity. They are equipped with a fabric that expands when the air becomes humid. The relative humidity is then displayed via a pointer and a scale on a dial.

Hygrometer-1

Analogue hygrometers can also be used as decorative elements.
(Image source: pixabay.com / rschaller98)

The disadvantage of analogue hygrometers is that they have to be calibrated regularly so that they do not become too inaccurate.

Advantages
  • Battery-free operation
  • Beautiful design
Disadvantages
  • Regular calibration
  • Limited functions
  • Often more expensive

The beautiful design of analogue hygrometers clearly speaks for them. Unfortunately, however, they can often only display humidity and have no other functions. They are also often more expensive than digital hygrometers.

What distinguishes a digital hygrometer and what are its advantages and disadvantages?

With digital hygrometers, the air humidity is measured by sensors and the values are then shown on a digital display.

Hygrometer-2

With digital hygrometers you can read the air humidity at a glance.
(Image source: pixabay.com / Projekt_Kaffeebart)

You don't have to calibrate this type of hygrometer. Moreover, the temperature is usually displayed in addition to the humidity.

Advantages
  • Do not calibrate
  • More functions
Disadvantages
  • Not so nice design
  • Batteries needed

There are also digital hygrometers that are equipped with a mould alarm. These hygrometers alert you (visually or acoustically) when the humidity is too high, i.e. above 60%. The disadvantage of digital hygrometers is that they run on batteries and often don't look so nice.

Buying criteria: You can compare and evaluate hygrometers based on these factors

Once you have decided whether you want to buy an analogue or digital hygrometer, the next decisions come up. There are several things you need to consider when buying a hygrometer. We have summarised the most important ones in the following lines to make your decision easier.

Measuring accuracy

When you buy a hygrometer, you naturally want it to display the exact values. Many manufacturers state the accuracy of their devices as +/- on the back of the product. This means that the device can deviate by +/- % from the exact value.

Instruments that have a measuring accuracy of +/- 3% are considered accurate.

However, the accuracy of hygrometers decreases over the years.

Mounting options

Most hygrometers can only be set up using a fold-out stand. However, if you want to hang your hygrometer, make sure you buy one that has a hole in the back. There are also hygrometers that have a metal strip so you can hang them, for example, on a refrigerator.

Other functions

  • Mould alarm: As mentioned above, there are digital hygrometers that are equipped with a mould alarm. If the humidity is too high, these devices trigger a visual or acoustic alarm to warn you of the increased risk of mould.
  • Data logger: Hygrometers with data loggers can store the measurement results for several months. You can transfer the stored values to a computer and evaluate them there.
  • Comfort zone indicator: Hygrometers equipped with this tool can show you in which range the air humidity is in this room. They show you whether the air is too dry or too humid, or whether it is in the optimal range. Many hygrometers show this by means of smileys.

Facts worth knowing about hygrometers

What should be considered when buying a hygrometer?

When buying a hygrometer, you should make sure that you buy one that is as accurate as possible. In other words, a hygrometer with a measuring accuracy of about +/- 3%.

Not every hygrometer is equipped with a mould alarm or a data logger.

You also have to decide whether you prefer an analogue or digital hygrometer. We have listed the advantages and disadvantages of each above. You should also be aware of which functions are important to you in a hygrometer. Depending on the purpose for which you want to use the hygrometer, different functions are useful.

Where should you place a hygrometer?

It is best to place a hygrometer in a central and easily visible position in the room. The room should be rather cool and less ventilated. It is better not to place the hygrometer near windows, heaters or behind a curtain. These places could falsify the measurement results, as could direct sunlight.

There are hygrometers that can measure humidity throughout the home.

However, if you already have problems with mould in your home, it is better to put a hygrometer in every room where you have mould problems. Rooms that are not well insulated, not regularly ventilated and unheated are prone to mould.

Hygrometer-3

The optimal humidity in wine cellars is about 70%.
(Image source: pixabay.com / leohau)

In wine cellars, cellars and greenhouses, you should use a hygrometer to make sure that the humidity is in the optimal range. Cellars and wine cellars tend to have too much humidity and in greenhouses, the right humidity is important for the healthy growth of plants.

How do you calibrate hygrometers?

You don't need to calibrate digital hygrometers, but you do need to calibrate analogue ones about twice a year. There are different ways to calibrate hygrometers, which we will now present to you.

Towel method: With this method, you have to make sure that the temperature in the room is constant and that there are no draughts. Then wrap the hygrometer in a damp towel and set it to 100% after ten minutes. This is the simplest method of calibration.

Salt method: First you have to put the hygrometer in a freezer bag. Then put about a tablespoon of salt in a glass and add a little water until it forms a kind of paste. Then put the glass in the freezer bag and close the bag. Then you wait two hours and after this waiting time your hygrometer should show a relative humidity of 75%.

Next, take a screwdriver and pierce the freezer bag to reach the hygrometer adjustment screw. Now you need to calibrate the hygrometer so that it reads 75%. The salt method is considered the most accurate method of calibration.

Photo source: Grabo14/ 123rf.com

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