Best Hygrometer to Monitor Relative Humidity/Temp for Pianos

Kevin Busse Mar 05, 2024
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Hygrometer with piano tools

Disclosure: Some of the links in this article may be affiliate links, which can provide compensation to me at no cost to you if you decide to purchase. 

It has taken lots of time and experience among technicians to find the most accurate hygrometer for piano tuning appointments that works accurately, for years, and across whole teams of piano technician/tuners.

I know how crucial it is to keep strict relative humidity and temperature parameters in order to preserve the tuning and overall condition of the thousands of wooden and metallic pieces inside of a piano for as long as possible.

In fact, all of my colleagues and some of the observant pianists I work with know this all too well, which is why we must find the best hygrometers to get accurate readings.

In my own experience, I have gone to countless piano tuning appointments over the last 10 years tuning, regulating, fixing up pianos, and without a doubt I can confirm how important closely monitoring relative humidity and temperature are.

Here is my expert advice based on what other technicians including myself have found to be the best hygrometer for relative humidity and temperature for monitoring pianos along with extra features I have learned about this device further down on this page.

Although I primarily use this device for acoustic pianos, this humidity meter can be used for other musical instruments to measure the humidity of the air.

This hygrometer ranks #8 on our list of 21+ Useful Gift Ideas for Pianists and Piano Lovers in 2024.

What’s the Best hygrometer for measuring piano humidity?

Extech Psychrometer RHT510

Piano Hygrometer

Extech psychrometer RHT510Hygrometer side by side comparison

Piano hygrometer accuracy and best results

Here I compare between a couple Extech Psychrometers.

As you can see, the relative humidity differs by 1.7% and the temperature in the room differs by 1.6 degrees.

Looking at it now, the accuracy looks pretty good.

However, in comparison to many other inexpensive hygrometers this is actually far superior because this device will operate closely on a consistent basis throughout the temperate climate in New York over a period of years.

When working in the winter, the device gets cold in my car. For each tuning, I then let the device thaw out over the length of the tuning so that it will give me the most accurate reading. It usually takes less than half the time of a tuning for it to fully thaw anyways, I like to take the reading at the end, however.

By the end of the appointment I will find that this device matches with the all trusted stationary hygrometers in customers homes and piano showrooms, excluding the hygrometers that are of low quality with bad readings.

hygrometer in bag with piano tools

Piano hygrometer placement among piano tools

I've found it to be a good idea to keep this in the center of my tool bag for in-home piano studio readings because of its importance.

It is a constant reminder that the fundamental component of piano maintenance lies in the ability to keep the room in which the piano sits at a constant relative humidity and temperature because of how wood swells.

Aside from taking out my piano tuning lever, I will reach for my hygrometer each and every single time I work on a piano in a customers home primarily to determine whether or not the relative humidity is between 35-50%.

What are the best Relative Humidity practices for pianos?

If the Relative Humidity is outside of a range between 35-50% then by definition the humidity of the room is not under control.

Not being able to dial back the humidity of a home with a touch of a button or by having a system of humidifiers/dehumidifiers setup will result in unacceptable environmental conditions for basic-level preservation of the condition of the piano.

*The cold air of an air conditioner is not enough to maintain a proper humidity level and cannot remotely compete with a humidity control system. In addition, a Piano Life Saver System is only recommended after the specific level of humidity in the piano room consistently maintains optimal humidity levels.

The good news is that I recommend a room humidifier for low humidity and a room dehumidifier for high humidity along with 10 Things to Know about The Piano Life Saver System that functions as a piano dehumidifier and piano humidifier.

Hygrometer relative humidity and temperature readings

Running the Extech RHT510 Psychrometer accurately

With a touch of the power button, I have the digital display is set to the relative humidity as well as the temperature, which is how I normally have it configured by default after the first initial setup, which because of the ease of use took a less than a minute to figure out.

It takes about 5 seconds for it to boot-up and display the parameters.

The Relative humidity tends to be most accurate quicker while the temperature range takes a few minutes longer to get the most accurate reading.

The best option I recommend to set it out for at least 10 minutes before powering it on to take a reading. This way you save power as well as waste less time looking at readings that have not matured.

The best place to take the humidity reading is on top of the music shelf. The best time to take a reading is at the end of the tuning appointment. The wrong place to take a measurement is on the floor, against a window, and near the ceiling.

Hygrometer with piano tools

Although relative humidity plays the most important role in maintaining the condition of a piano over time, temperature comes in a close second place, which is why it is helpful to see these two metrics clearly displayed on the screen.

The minimum and maximum relative humidity that it can accurately capture is between 10-95% relative humidity.

User Manual Information on the Extech RHT510

In the User Manual it states that the accuracy is + or - 4% which is extremely generous on paper. In practice, I've only seen this device have discrepancies of less than 2% in relative humidity between the exact same devices.

This device will measure the lowest temperature at 32 to 122 degrees fahrenheit at the highest temperature. So long as the piano is not in a location that has sub zero temperatures, then this hygrometer will do just fine on a day-to-day basis.

The User Manual also states that the accuracy of temperature readings in Fahrenheit is + or - 2.5 degrees which I also think is generous to say.

This device has impressed me with it's accuracy, consistency, and longevity. Holding the device and breathing within a couple feet of the device will distort the reading, which is why it comes with a tripod capable in-thread at the back of the device.

Maintenance of the Extech Psychrometer

Extech Psychrometer batteries triple A

Battery information for the Psychrometer

This hygrometer has 3 triple A batteries equipped inside of it.

I've owned this for 3 years now and have had to replace the batteries twice. The compartment can be unscrewed by using a dime from your spare change collection if you really don't have a flat head screw driver.

One of the reasons the battery is able to last for so long is because the device will shut off after 10 minutes of inactivity.

Interestingly enough, I did not activate the APO (Auto Power Off) for my device until I wrote this post. I will have to update this page when I learn how much longer the batteries can last.

Scroll down for details on how to activate the APO (Auto Power Off).

Hygrometer Auto Power Off Setting

Auto Power Off Feature

Be sure that "APO" (Auto Power Off) is displayed under the battery icon so that you know the device will power off automatically after 10 minutes.

Although, you may choose to have the APO (Auto Power Off) disabled so that it does not auto shut-off.

Having said that, about once a year I have had to replace the batteries without having this feature activated.

I store my tool bag in my cold car during the winter and during the hottest days of the summer, so getting 1 year of life out of these small batteries is pretty good if I say so myself.

CMM880 Digital Handheld Thermo-Hygrometer

Hygrometer piano relative humidity temperature

Here is an example of when I used the CMM880 Digital Handheld Thermo-Hygrometer.

This hygrometer seemed to work well and was highly sensitive to changes in humidity while holding the device and breathing within a nearby range of the hygrometer.

However, as time went on, while it continued to be extremely sensitive to even small humidity changes, it did not stay consistent across the dozen of the exact same hygrometers with the team of piano technicians and tuners that I work alongside with.

Due to discrepancies in readings by the end of the few years using this device, it was decided to no longer use this hygrometer from Mannix.

Hygrometer comparison temperature and relative humidity

Comparing my old hygrometer

As you can see, the CMM880 was 1.6% away in Relative humidity and 1.4 degrees away from the trusted stationary hygrometer that stays mounted on the wall in a piano showroom.

This reading looks great at face value. However, in comparison with other hygrometers made by Mannix, it did not line up consistently among all of them within a few years of working with this device.

When it is brand new it works very well, however, as time goes on it performs less accurately against the same other CMM880 models.

What are the Features of the Extech Psychrometer RHT510?

  • Backlighting

  • Celsius & Fahrenheit

  • Tripod mount

  • Dew Point Temp

  • Wet Bulb Temp

  • Type K Temp

  • Record Maximum and Minimum Temp/values overtime

  • Auto Power Off

  • Ability to remain on

  • Display "Hold"/Pause the Display

  • Battery life indicator

For the most part, I only use the device for the Relative Humidity and Temperature accuracy features.

There are lots of other things this device can be used for which I learned about after reading the short 7 page Users Manual.

Extech Pschrometer schematic

  • Type K temperature probe sold seperately

  • Tripod sold seperately

From the humidity sensor to the tripod mount in the back, here are helpful details on where everything is located.

Extech Psychrometer RH510 LCD Description chart

From the APO (Auto Power Off) icon to the Type K temperature icon, the LCD descriptions can be found here.

Backlit Extech Psychrometer

Backlight the LCD screen

Just press the light bulb icon to turn on the backlight to illuminate the LCD screen for an easy-to-read display.

The light will automatically switch off after 10 seconds of use.

During the day the backlight doesn't look like it does much, but when there really isn't any light in the room it lights the whole screen up so that it is easily readable in dark conditions.

This really helps especially in instances where the customer's home doesn't have great lighting in the room where the piano is located.

Record as levels fluctuate using the record mode

Pressing the "R" (Record) button will start the record mode. When you are done recording, press the button one more time to exit the record mode.

After the record mode has started and ended between the two times the "R" button is pressed, you may toggle between viewing the high and low readings by clicking the R button.

Long press the "R" button to exit the record mode.

Hold/Pause Screen

By pressing the "H" (Hold) button will pause/hold the screen.

This allows the user to walk around with the humidity/temperature levels taken at the piano, while being able to transport what's displayed on the LCD screen to any location where the piano owner may be in order to show them if they are not nearby.

Press the "H" button to unhold/unpause the screen.

Choosing Celsius or Fahrenheit

  1. Long press SET button. The bottom display will show ‘PoFF’.

  2. Press the R button. The bottom display will show t-CF’.

  3. Press the ▲ or ▼ button to select C or F.

  4. Press the R button to save the selection.

  5. Wait approximately 10 seconds for the meter to return to normal operation.

Auto Power Off (How to set to on or off)

Hygrometer Auto Power Off Setting

It's useful to know that the APO (Auto Power Off) must be on display underneath the battery life icon in order to preserve the battery life.

Even though I recently discovered this functionality, it takes about a year before I have to replace the batteries even without this feature.

Hygrometer auto power off yes

Press the downward arrow/"set" button so that the screen will display "No PoFF" or "Yes PoFF."

Be sure that the LCD screen displays "Yes PoFF" in order to have it on the correct setting to prolong the battery life by turning off the screen after 10 minutes of inactivity.

If you leave the screen on "No PoFF" then that will ensure that the battery will run out faster by having the screen permanently on unless you press the power button.

Hygrometer save auto power off setting

In order to save your settings, click on the "R" (Record) button.

Wait 10 seconds so that your settings are properly saved.

Now, your device will display "APO" (Auto Power Off) underneath the battery life icon.

Extech RHT510 General Specifications

Extech Psychrometer useful information

These General Specifications taken from the User Manual show useful information that I didn't know about this device.

For instance, the "Input Overload Display" reads "----" when there is an overload. Thankfully, in the few years that I've used this device, I've never seen that appear on the display screen.

All of the other specifications are good to know, however, I didn't find them particularly important as a piano technician/tuner.

Definitions for lesser used modes of the Hygrometer

What's Dew point?

That's the temperature at which the air cannot hold any additional moisture.

For example, the dew point is reached it causes condensation against windows, blades of grass, and conditions for rainfall.

*It's important for the room that a pianos sits in to never reach this point because strings may rust in especially salty aired environments like near the ocean.

This device is able to accurately measure the Dew point when environmental conditions are between -13.5 to 120.0 degrees Fahrenheit.

What's wet bulb temperature?

That's the lowest temperature that an object can reach if it were covered in a wet cloth from heat loss due to the evaporation of water.

For example, on a summer day if you held a wet cloth over your hand it can only get so cold in the wind before it doesn't get any colder.

*This information is not particularly useful to piano technicians, however it's a neat feature that this psychrometer has.

This device is able to accurately measure Wet Bulb Temperature when the environmental conditions are between 22.2 to 120.0 degrees Fahrenheit.

What is does the Type K Thermometer measure?

From what I understand, this is applicable to a wide range of extremely cold (-148 degrees Fahrenheit) to extremely hot (2,372 degrees Fahrenheit) environments that may have corrosive elements involved in taking the measurements/readings.

This device is able to accurately measure Type K Temperatures when the environmental conditions taken from the Type K probe measure between -148 and 2,372 degrees Fahrenheit.

*This information is definitely not useful to piano technicians, but hey, you learn something new everyday!

For a more detailed and accurate answer to this question about Type K Temperatures, this is not the place. I'm a piano tuner for crying out loud!


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Disclosure:  Some of the links in this article may be affiliate links, which can provide compensation to me at no cost to you if you decide to purchase.