Hygrometers measure the amount of water in the air, what’s known as humidity.
Knowing the amount of humidity is important in storage areas, museums, archives, server rooms and any places where too little or too much moisture can cause damage to items.
You can also use a hygrometer to keep your home comfortable. By measuring and adjusting both temperature and humidity (most hygrometers can also measure temperature), you can greatly improve indoor comfort.
There are different types of hygrometers ranging from high-end advanced hygrometers for professionals to simpler models designed for residential measurements.
What to Consider When Choosing a Hygrometer
a) Types of Measurements
All hygrometers measure relative humidity (RH). This is the amount of water vapour in air relative to the total amount of water vapour it would hold at the same temperature. It is expressed as a percentage.
Many hygrometers also measure the dew point. Dew point is the lowest air temperature at which relative humidity is 100%. Beyond this point, water vapour in the air would turn into liquid water to become fog or dew.
Dew point gives a more realistic understanding of how humid a place is. That’s why dew point hygrometers are preferred where precision humidity measurements are important. They are also ideal for measuring small amounts of moisture in an environment.
Some hygrometers also measure the wet bulb temperature (these hygrometers are called psychrometers), which gives further understanding of the humidity of an environment.
Wet bulb temperature is especially important in determining whether an environment is safe for humans and animals (e.g. during a heatwave). A wet bulb temperature over 35°C can be fatal.
Not all these measurements are important for everyone. If you are buying a hygrometer for home use, relative humidity is enough.
Dew point and wet bulb measurements are more useful in commercial, industrial and public settings.
b) Measurement Range
Advanced hygrometers can measure humidity between 0% and 100% while cheaper models have a smaller range – usually between 10% and 99% RH.
Measurement range is important if you anticipate working in a wide range of weather conditions.
Also check the temperature range. Some hygrometers can measure up to 200°c or more and as low as -20°c.
As with humidity, the ideal temperature measurement range depends on your needs. If you’ll be working in different climates and varying weather conditions, look for a hygrometer that can capture a wide range of temperatures.
c) Accuracy & Resolution
Accuracy and precision go hand in hand when it comes to precision (although you can’t forget calibration).
Accuracy is typically expressed as the margin of error. The most accurate hygrometers have an accuracy of ±1% RH while residential hygrometers have an accuracy of ±5%.
Resolution is the smallest change in humidity a hygrometer can measure. A smaller change (high resolution) allows you to take more precise readings.
The best hygrometers have a resolution of 0.1% RH.
Don’t forget to also check the accuracy and precision of the built-in thermometer. Accuracy ranges between ±0.1°c and ±1°c depending on the cost of the hygrometer. Standard temperature resolution for most hygrometers, even the cheaper ones, is 0.1°c.
d) Data Hold and Min/Max Functions
Data hold is a convenient feature in hygrometers that allows you to freeze a reading on the display. This gives you time to carefully read and record the measurement. You can even walk away from the measuring area without losing the reading.
Some hygrometers also have a peak hold button, which tells the hygrometer to freeze the highest recorded measurement.
Another function to look for is min and max, which displays the lowest or highest reading on the screen.
e) Handheld or Wall Mounted
If you need to measure the humidity of different rooms or places, a handheld hygrometer is the best. It’s smaller and thus more portable. If you need to take measurements of a place for a prolonged period, look for handheld hygrometer with a tripod attachment (you may have to buy the tripod separately).
If you want to monitor the humidity and temperature of one room, get a wall-mounted hygrometer and install it somewhere you can easily see it. Alternatively, look for a desk hygrometer with a tilt base.
f) Display
The display should be backlit and large enough to see the readings on it without straining your eyes.
Handheld hygrometers generally have smaller readings since you are supposed to hold it close to your face when reading measurements.
Wall mounted hygrometers or those designed to sit on a desk have larger screens so that you can check the current humidity and temperature from a distance.
If you are buying a hygrometer for home use, get one of those wall-mounted ones with extra-large screens and numbers displaying current relative humidity and temperature. You’ll be able to see the readings from across the room.
Some hygrometers also display the current time, essentially functioning as a wall clock.
- Read also: How To Choose The Best Sound Level Meter?
g) Data Logging
A hygrometer with internal memory can store several hundred or thousand measurements. This is handy if you ever need to refer to previous readings, e.g., when analysing weather trends.
h) Connectivity
Some professional hygrometers have USB or wireless connectivity (Bluetooth or WiFi), which allows you to transfer data to a computer for further analysis.
Some residential hygrometers also have WiFi connectivity. You can check a room’s humidity and temperature even when at work or on vacation.
Best Hygrometers: Reviews
1. Extech RHT510 Hygro-Thermometer Psychrometer Review
The Extech RHT510 is ideal for professionals as well as consumers looking for a handheld hygrometer that measures more than just relative humidity.
The Extech RHT510 hygrometer measures four things: relative humidity, temperature, dew point and wet bulb temperature.
Accuracy for relative humidity is ±4% RH and the resolution is 0.1% RH. Resolution for all three temperature measurements (air, dew point and wet bulb) is 0.1°C.
As for range, it is 10-95% for RH, 0-50°C for ambient temperature and -100°C to 1300°C when using the type K temperature sensor.
The Extech RHT510 is designed for one-handed use. It easily fits in one hand and has grips on the side to keep it from slipping.
The backlit display is easy to use in any lighting condition.
The control panel has buttons for HOLD and Min/Max functions.
2. Testo 0560 6230 Hygrometer Review
The Testo 0560 6230 Hygrometer is the best choice for commercial climate monitoring in places like museums, server centres and other humidity-sensitive environments.
The Testo hygrometer features an extra-large display that shows lots of information including a histogram, temperature, relative humidity, date and time.
You can set temperature and humidity thresholds for the room. If the room goes past these thresholds, an alarm in the Testo hygrometer goes off to alert you.
The control panel is on the side of the display. It has buttons for displaying max and min readings, setting an alarm and switching between the temperature and humidity histograms.
The Testo hygrometer holds measurements for up to 90 days. You can recall previous readings on the display.
Unfortunately, there doesn’t seem to be a way to transfer data to a computer for further analysis.
The Testo hygrometer measures just two things: temperature and relative humidity.
Temperature measurement range is -10 to +60°C with an accuracy of ±0.4°C and a resolution of 0.1°C.
The RH range is 0 to 100% RH with a resolution of 0.1% RH. Accuracy is ±2% + 1 RH at a relative humidity between 10 and 90% and ±3% RH for other RH values.
As for installation, you have two options: place it on a desk or table or mount it on the wall. The hygrometer comes with a tilt base if you prefer to place it on a desk as well as a hanging bracket if you prefer to mount it on the wall.
3. CHAUVIN ARNOUX C.A 1246 Hygrometer Review
The CHAUVIN ARNOUX C.A 1246 is the best choice for professionals looking for an advanced handheld hygrometer.
It is pricier than most hygrometers, but is packed with useful features.
The C.A 1246 hygrometer measures three things: relative humidity, dew point and ambient temperature.
The RH range is 3.0-98.0% RH while the ambient temperature and dew point measuring range is -10 to 60.0°C.
Readings are shown on a large screen that is backlit for easy viewing in any lighting. You can set temperature and RH thresholds, past which the hygrometer will sound an alarm to alert you.
The control panel is simple to use with just a few buttons for max/min, hold, record, temperature unit change and Bluetooth connectivity.
The CHAUVIN ARNOUX C.A 1246 has internal memory that stores up to a million measurements. It also allows data transfer via Bluetooth or USB – handy for pros who need to do additional analysis and calculations on a computer.
To ensure safe use in any kind of environment, even outdoors, the C.A 1246 hygrometer is housed in a IP54 casing for dust and water protection.
4. Extech Instruments 445703 Big Digit Hygro-Thermometer Review
The Extech Instruments 445703 hygrometer is perfect for homes, offices, greenhouses and any spaces where continuous humidity and temperature monitoring is required.
The large 1” digits on the display make it easy to check the indoor climate at a glance even from a distance. The screen is backlit for easy viewing under low light conditions.
The hygrometer comes with a bracket for wall mounting. If you’d rather place it on a desk or surface, use the included stand.
The Extech hygrometer measures relative humidity and ambient temperature.
The RH range is 10 to 99% RH with an accuracy of ± 5% RH (between25 and 80% RH). Temperature range is -10 to 60°C with an accuracy of ±1°C (between -10 and 50°C).
The display can show max and min readings.
5. Extech Instruments 445702 Hygro-Thermometer Clock Review
If you’d like a large display hygrometer that also shows the time, we recommend the Extech Instruments 445702.
The hygrometer has an extra-large display divided into three rows showing the time, temperature and relative humidity. This way, you don’t have to choose what to display on the screen; you can check the time and indoor climate with just a quick glance.
Buttons below the display let you set the clock, display the max and min readings, reset the hygrometer and access advanced settings.
Like most basic hygrometers, the Extech Instruments 445702 measures only relative humidity and temperature.
The RH range is 10 to 85% with an accuracy of ±6%. The temperature range is -10 to 60°C with an accuracy of ±1°C.
Considering the narrower RH range and lower accuracy, the Extech Instruments 445702 is best for residential use.
You can mount the hygrometer/wall clock on the wall using the included bracket or place it on a table using the built-in tilt stand.
The hygrometer runs on an AAA battery (included).
You seem to have missed out an important factor – calibration.
Many years of experience and testing RH meters show that user calibration is necessary to ensure long term reliability and accuracy.
A measurement precision of 0.1%RH is meaningless when the accuracy is only +/- 4%.
Which of your recommendations enables user calibration?
Hi, I’m needing to measure ‘damp’ reported in rented properties to determine whether it is damp or condensation from the way te tenants are living. The meter will need to be left in the property for several days and the data extracted when the unit is retrieved. What would you recommend for this please?