Piano Humidity Control and Tuning Stability

Why pianos go out of tune

The top 3 reasons are:

1.  Humidity Change
2.  Humidity Change
3.  Humidity Change

Note: The above is really an analogy that helps lay people understand the concept of how soundboard/bridge expansion occurs with increased humidity resulting in increased string tension. HOWEVER… it is flawed. I believe flexing in the cast iron plate accounts for most of the change. HOWEVER…I believe the expansion of the wooden structure of the piano (the soundboard and the large beam bracings in back) cause flexing in the plate that results in the piano going out of tune.

The most solid proof of this is the Yamaha electric grand. This is very small baby grand made by Yamaha in the 1970’s. It was very much like an acoustic grand piano but lacked a soundboard. Small electromagnetic sensors (pick-ups) created a signal that could be amplified and played through a speaker system. I was surprised to find these pianos  go out of tune in a similar way to normal pianos, even though there is not a soundboard. When I’ve raised pitch (significantly increasing the tension across the entire instrument) on these pianos the pitch creeps backwards around 20%, which is exactly how regular pianos behave. This is compelling evidence that plate flexing plays the major role in tuning instability.

Number 4:  sudden temperature change. The strings can be sensitive to sudden cooling or heating. However, as the temperature of the cast iron frame that supports the strings’ tension equalizes with the strings, the tuning will recover to a large degree. Also, the temperature does affect the relative humidity of the air. Warm conditions dry pianos out, and cold conditions can have a humidifying effect.

Try this experiment! 

This works best on a grand because of the easier access to the strings, but could work on an upright with the front panel off. Simply pick one of the easy to access strings in the midrange of the piano (C above middle C is good) and rub your finger up and down the length string quickly several times. Now listen! You will really hear how a bit of heat can make a string go out of tune. Wait a couple of minutes, and listen again. The note is back in tune! 


Number 5:  Hard and intense playing. Certainly pianos that receive hours of heavy-duty use each day will deteriorate much more quickly than a lightly played piano. However, if the humidity doesn’t budge, you should be able to bang on it all day long and not have the tuning budge much. The voicing, however, will need regular attention to maintain good tone.

Myth: Never put your piano against an outside wall! 

That rule may have made sense a century ago before modern building codes and wall insulation. This is especially true in extreme weather climates like Chicago or New York where humidity can swing between 90 percent in the summer down to 10 percent in the winter. The outside wall rule can now be thrown into the category of “old wives tales”.

Here’s a good article on piano placement from the Dampp-Chaser corporation.

Piano makers without exception recommend at least two tunings per year.

The reason they do this is to cover themselves. If a person buys a beautiful new grand piano for $40,000 and it goes out of tune after few months, the person might think there is something wrong with the piano and that it doesn’t hold a tune well. The manufacturer recommendations create the expectation that tuning is somewhat temporary and will require ongoing maintenance.  

The “Dirty Secret” of Piano Tuning. Shhh! Don’t tell anyone!

“If you wait longer, it may actually get better!”

Could this really be true? Could a piano be in better tune after a year than after 4 months. I can assure you that it is certainly true, and I have seen it many hundreds of times in my 20+ year career as a piano technician.

When I see a piano in exactly one year, it is almost invariably in better tune than when I see it after a few months.

Why? The reason is the average humidity at any given time of year is similar to that of previous years. Not exactly, but similar enough that the tuning can correct itself to a surprising degree.

Q: What is “Relative Humidity (RH) anyways?

A: It is the amount of water in the air relative to the amount of water vapor the air can hold. Cold air can hold very little moisture, warm air can hold a lot. Think of the air as a measuring cup that gets larger or smaller depending on the temperature. If the cup is outside on a 30 degree winter day it may be full to the brim. But when you bring the cup into a 70 degree room it may get twice as big. The amount of water is the same, but because the cup is now bigger, it is only half as full or 50% relative humidity.

Q: What’s the ideal humidity level for a piano?

A: Between 40 and 45 percent

“A relative humidity level (RH) of approximately 45% is ideal” – Kawai owner’s manual

“Generally speaking, a relative humidity of between 40 and 45 percent is ideal for pianos.” – Yamaha’s official website

Manufacturers like to say that [pianos do best with] humidity about 45 percent. -Larry Fine’s Acoustic Piano Buyer

Humidity Trends in the Pacific Northwest

I regularly measure humidity in my clients’ homes. Over the years I notice fairly consistent patterns. In the summer, the relative humidity often averages around 65 percent dropping down to around 55 percent in the late fall and finally down to the 40’s in the winter. Occasionally we get humid spells in the summer with the humidity jumping up to 70 or even 80 percent. Likewise, a good cold snap in the winter can drive indoor humidity down into the 30’s.

Thus, we don’t really have to deal with dryness much in the Puget Sound, because the humidity can be close to ideal in the wintertime. It is the summertime humidity, and the subsequent swelling of the wooden components of the piano’s structure that makes our pianos go out of tune. That’s why the basic humidity control system (heating rod + humidistat) can be effective at keeping the pitch stable. During the occasional cold snap, running a room humidifier or keeping a tea kettle on the stove can keep the piano from become overly dry.

Rule: the colder it is outside the drier it is indoors.

Cold air can’t hold as much moisture as warm air. When cold air is brought indoors and heated to around 68 to 70 degrees, its relative humidity drops significantly. That is why winter is the driest time indoors. This can be counter-intuitive for clients who think that the winter rain and cold would cause the indoor humidity to be higher.

Fortunately for us in the Puget Sound, indoor humidity during the coldest months is close to the ideal of 45 percent. However the gradual increase in humidity from Spring into Summer is where problems arise.

A basic piano humidity control system is designed to take care of the piano during the summer months when average  humidity typically runs in the 60-70 percent range.

Don’t throw away your tuning dollars!

Believe it or not ~ I have seen pianos literally go out of tune in a week due to sudden humidity change.

Measuring Humidity and Pitch of Your Piano

One of the best ways to educate yourself on the effects of humidity is to purchase a humidity measuring device known as a hygrometer. Here is an inexpensive hygrometer (humidity measuring device) that is available from Amazon for around $10
It is called the ACU-RITE Backyard Weather Humidity Monitor

The readout gives current relative humidity and temperature and also tells you what the high and low have been in the last 24 hours. These inexpensive hygrometers are not known for their precision. However, for the purposes of protecting the stability of your piano’s tuning, absolute accuracy is not of paramount importance. Having a generalized idea of what the humidity is doing is the key.

There is an easy method of calibrating hygrometers by sealing them in a bag with table salt. Here is a fun description of the process.

If you are willing to spent around $100 you can get a hygrometer that will take regular temperature and humidity readings that can be downloaded onto your computer. This allows you to see a graph of the temperature and humidity readings over several weeks or months.

Measuring the change in your piano’s tuning

If you have a good musical ear and are sensitive to tuning changes, simply keeping an eye on your hygrometer and listening to your piano will help you make the connection to how the weather is affecting the tone. If you are not confident in your ability to detect out-of-tuneness, you can use an ap on your smartphone are an inexpensive tuner.

Screenshot of Tunelab for Android

Tunelab is a professional quality piano tuning ap available for Android phones and tablets. The full version sells for $350, but there is a shareware version that is fully functional. The only limitation of the free version is that it regularly freezes for 2 minutes in order to give you time to contemplate buying the full version!

To see how your piano is affected by humidity changes you will want to measure a few sample notes.  I recommend the last plain wire string before the copper wound bass strings begin.  Another good sample note is the very top note of the bass section.

When a piano goes flat, these notes will go extra flat. When it goes sharp these notes will go extra sharp. It’s also a good idea to measure A above middle C. This is sometimes called A440, and if the piano has just been tuned to standard pitch, it will be vibrating 440 cycles per second. When the humidity goes up for a week or two you may see A440 creep up to A441, or even A442.  If the piano gets dry it can easily drop down to A438, or in places with extreme winters, A437 or lower.

Right after your piano is tuned, ask your technician to make a note of the frequency Hz (vibrations per second) of your samples. You will want to write this down along with the current humidity. This will give you some data to compare future readings after the weather changes.

Caution: Don’t over-humidifier your house during a cold snap!

If you live an a climate that gets very cold in the winter, there are limits to how high you can let your indoor humidity get. During extreme cold spells, trying to keep the indoor environment at 45% relative humidity will damage your home by causing condensation inside the walls. Heating/Cooling specialists have charts listing the maximum humidity level indoors for a given outdoor temperature:

    Outside Temperature                        Inside Humidity

                        20º to 40ºF                                          Not over 40%

                        10º to 20ºF                                          Not over 35%

                        0º to 10ºF                                            Not over 30%

                        -10º to   0ºF                                         Not over 25%

                        -20º to –10ºF                                       Not over 20%

                        -20ºF or below                                     Not over 15%

Q: When’s the best time of year to tune my piano?

This is a frequently asked question that is tricky to answer. It depends on several factors. If you want to maximize the length of time your piano will sound acceptable, the best time to tune would be when the piano has been at an average humidity level over a period of 2 or 3 weeks. This usually means tuning the piano in the spring or fall and avoiding the extremes.

If you refer again to the charts near the top of this post, you will see that pianos have a driest point and a most humid point during the year. If you can have the piano tuned when it is right in the middle, the chances of the piano sounding acceptable throughout the year will be greater.

Some people love to play their piano over the Christmas holiday. For some, that is the ONLY time of year they play their piano. In that case it would make sense to tune it right before the holiday season, so you can enjoy the best sound. Other clients may play more in the summer when they have time off.

This is another reason to consider installing a humidity control system in the piano: The time of year becomes a little less important.

A True Story

My most talented client ever, Charlie Albright, lost power in his home in Centralia one winter. The house got very cold. When the power came on Charlie called me complaining about how bad his piano sounded. I told him to wait a couple of weeks and check in with me again. After two weeks Chalie called to say “it sounds fine now!”.

If I had tuned the piano right after the power came on, it would have quickly gone out of tune.

I take a great deal of pride in the quality and stability of my tunings. However, the most stable tuning in the world will only last as long as the humidity remains at the same level as when it was tuned.

A Dampp-Chaser system is one of the best assurances I know of to preserve the quality of my tunings. That is why we put them in the pianos we sell. That is why I recommend them to all my clients. Consistently the pianos that have a system are in much better tune when I arrive to service the piano than those without. This gives me more time to address other service needs of the piano besides tuning: Cleaning, voicing, regulating, etc.

Another true story: I arrived at a local piano teacher’s home during the summer  to tune her grand piano that I had tuned the past January. The piano had gone significantly sharp with the higher humidity and the tuning was really bothering her.  After some discussion she agreed to forego the tuning and instead had me install a Dampp-Chaser system. 2 weeks later at the monthly Olympia Music Teacher’s Association meeting, she was happy to tell me how much better her piano sounded already! The system dried the piano out and made its humidity level closer to where it was when it had last been tuned.

Q: “Won’t these humidity control systems put you out of a job?”

A: The systems are not perfect. It is true that a piano owner may find he/she can greatly extend the interval between tunings. However, tuning is just one aspect of the maintenance of a piano.

“tuning is just one aspect of the maintenance of a piano”

When I show up to service a piano that has a system installed, I am usually able to spend more time cleaning, controlling friction, and regulating touch and tone.. These are separate issues from tuning yet are equally important in order to get the most enjoyment of the instrument.

How much do they cost?

Basic Upright System: $275 + tax
Basic  System for grands under 6′: $325 + tax
Grands over 6′: $399 + tax

Dampp-chaser systems install out of site inside an upright piano or underneath a grand.

We recommend having the piano tuned 3-4 weeks after installation or as needed.

Suggestions for keeping your piano in tune:

    • Have a certified Dampp-Chaser technician install a basic humidity control system in the piano. If you live in a climate that experiences very cold winters, then invest in the more expensive full system.
    • Get a digital hygrometer and put it near the piano so you can actually watch what the temperature and humidity are doing.
    • Get a free tuning app for your smartphone or tablet computer that will allow you to measure the low, middle, and high C, so you can see how humidity change is affecting the pitch of these notes.
    • Run a humidifier in the winter if the humidity is dropping below 40 percent. Even a $20 unit is adequate, or a tea kettle on the stove. Caution – If you get much sub-freezing weather, too much humidifying can damage your home. 
    • Avoid having the piano tuned right after unusually humid or dry weather
    • Using an air conditioner in the summer months will keep the humidity closer to the ideal range.
    • Keeping the room cooler during the coldest months of winter will actually keep the piano from getting too dry.
    • Keep the piano away from direct sun and heating vents

For less than the cost of 2 tunings, you can help insure the tuning stability of your piano and improve your listening pleasure throughout the year

I think of these systems as my little assistants, helping keep my clients’ pianos in better tune until my next visit.  We like to install systems on the pianos we bring into our shop to refurbish and resell. This saves me time and energy, because I don’t have to retune all the pianos after a weather change! Sometimes pianos will be in our shop for over a year before the right buyer comes along. With the system installed, they are always ready for a showing, and don’t require extensive retuning. 

Dampp Chaser Corperation, 
Piano Technicians Guild Technical Bulletin #3: Humidity Control
Mayo Clinic Article on indoor humidity and your health
Excellent article on how relative humidity affects wood furniture
Caring for Your Piano – pianobuyer.com
How to Calibrate your Hygrometer
Accurite $10 Hygrometer
Tunelab Piano Tuning App for Android


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