I was reading the article "WHY PIANOS GO OUT OF TUN (FASTER THAN THEY SHOULD)" by Erni Juhn, RPT in the PTG PACE Tuning Examination Source Book. Near the end of the article he recounts a case where a piano owner claimed that her piano was stable for 4 years, then suddenly became unstable and neither she nor her normal tuner could figure out why. Ernie came in and asked if the piano had recently been moved from a different house and the answer we yes. He then found out that the current house had radiant heat, and that was the answer as to why the piano's stability took a nosedive. He didn't detail how much of the cause was the radiant heat, but my interpretation was that it was the main culprit.

Is radiant heat generally bad for piano stability? I had not heard this before.

Radiant heat is a form of heating where a heated liquid is pumped through tubes just under the floors of living spaces. The heat is transferred by radiation rather than conduction or convection. It does tend to heat objects sitting above it more than forced air heating does. For instance, it's common practice not to run the tubes under the location reserved for the frig. If that's the case, I guess it does make sense that it could be a no-no for pianos. But if it is, I'm surprised that I've never heard of this before.

If it is bad for pianos, is there a way to have a piano in a house with radiant heat? Perhaps a piece of shiny sheet metal under an upright would work, as shiny metal is used to reflect radiant heat. But what could be done with a grand? Shiny metal under the carpet?

My guess is that radiant heat is just as uniform as forced air heat in most cases. What makes a difference is the fact that radiant heat has no chance to add moisture to the air, while a forced air system can have a humidifier on it. Even if a house has no humidifier, forced air circulates the air and humidity that arises naturally from everyday living, such as cooking, house plants, showers, cleaning, etc. With radiant heat, the humidity from daily life many not propagate to the "music room".

Robert Scott
Ypsilanti, Michigan

In a case like this, I always question whether the piano was actually "stable for a 4 full years" or whether it eventually just went out far enough for the client to finally be able to hear it and so, now, all of a sudden it "just went out." How often haven't we all heard this one? "It just all of a sudden went out?" No, I didn't. It has actually been going out all along but, finally became bad enough for your ear to just now, hear it....

The reason IMO, the pianos tuning took a nosedive was because it was moved from one home to another. One home with a certain RH to another with a different RH factor.

That's what I think too, FWIW. RPD

All,
I just found that there is another thread on this same topic from a little over a year ago. It's at http://www.pianoworld.com/ubb/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=3;t=004322;p=0 .
There are a lot of opposing views presented in it. They can be broken down into two categories: 1) Why radiant heat should or shouldn't be bad for pianos from a theoretical standpoint. And 2) Experiences people have had with pianos and radiant heat. Unfortunately, for both categories, there are numerous views both for and against. So it's not very conclusive.

My question is how far out does a piano have to be to be considered "out of tune"... 0.5 cent, 5.0 cents? more than 10.0 cents? If a tuning forks frequency can change with just a few degrees, just how much can one expect a piano to stay "in tune" and for how long.

Is there (and I'm sure someone has researched it) data on this subject. Is there someone that has taken a piano in a controlled temp/RH environment and recorded info? just curious

No offense to anyone but, to me, I think it's silly to try and guess when we can hear it and when it considered out of tune and by what measurements or standards. There are far to many variances from one human ear to another.

What one person thinks sounds marvelous, the next might think, well, it's passable and the next might think it sounds terrible. That's why we hear every day after finding a piano that hasn't been tuned for 20 years "it sounds okay to me yet!"

In my, not so humble, opinion, to me, if and when, the piano is out of tune even less than half a beat, IF, to a well trained piano technician's ear it sounds a little out then, it's out of tune. Doesn't matter what measurements are what.

If it is not on pitch well, then, technically, it is also out of tune IMO. I'm sure others might disagree with that one but, it doesn't matter. Sure, it can be in tune with itself and off from pitch however, were we to change the pitch, we would then also have to change everything else too which means, A/439 is not, A/440...

It changes very drastically with the environment and from state to state. Day to day, heat up, heat down. Heat blowing on the piano? Cold air blowing on it? Sun hits it? Open a window near it? A door opens up, some kid leaves it open.. All of it knocks it out quickly. Move it to an uneven floor? Moving it back and forth a lot, bumping into walls in colleges etc... To many factors involved to say well, it will stay in tune for x amount of time. BANG on it and it'll change.

That's why we tune before, during and after each concert. Within a couple hour period, it'll drift. Hot lights above? Hard piano playing for a long time? The list is almost endless.

Dampp Chaser has taken controlled stats of pianos with and without their systems on it. I don't recall where the evidence is located, perhaps on the Dampp Chaser website?

So, how long will it stay in tune? Not very... To a well trained ear.

Radient heat is more stable than forced air. It uses the thermal mass of the concrete to keep the temperature uniform. If you live in a humid area in winter, forced air dries out the air but radient won't. There is not much air circulation with radient so miniclimates could become a factor. Air circulation is the mixer for the humidity in the air.

She says: "The piano was stable for 4 years." Translation: "I haven't had it tuned in 4 years and it sounded ok to me." It was just sitting on the edge of a cliff ready to go.

I had always understood there to be a definite and predictable relationship between air temp and RH. IOW, when you bring cold, outside air in and heat it, the RH drops, being relative to the temperature of the air mass. Is this somehow not true with radiant heat?

The few pianos that I have encountered in radiantly heated spaces seem to do poorly, but these spaces were (IMO) overheated, so I couldn't make any definite judgement.

Certainly that is true with radiant heat. A psychrometric chart is a good visual way to understand it.

However that assumes no additional moisture added or subtracted. This is area where the systems might differ. If a furnace is drawing combustion air from the space, then it is being continuously replaced by outside air at colder temperatures. When that outside air warms up, it will have a low RH, and mixed with your inside air will bring down the overall RH.

Either radiant or forced air may have a furnace, and either may draw combustion air from the space or from outside. (You can see this if you have a fireplace, which draws all the combustion air from the house, and sends it up the chimney. You feel warm in front of the fire by radiant heat, the rest of the house becomes ice cold.)

The rest of the fresh air that enters does so by infiltration - coming through the leaks in the walls, windows, roof, floor, etc. The pressure changes caused by pumping heated air into the space and withdrawing "return" air might make that worse. But also houses vary greatly in how tight they are due to construction practices. You could easily have a tight radiant house and a loose forced air, or vice versa.

It is true that forced air is far easier to add a humidifier to. I've never liked this, as control is difficult in the average system, but it can work.

Everyone is making the assumption that the piano hadn't been tuned for 4 years but that's not the way I read it. Ernie Juhn knows his stuff. I don't think he would have made that observation if the owner hadn't been tuning the piano regularly.

In my experience, grand pianos do very poorly with radiant heat. It collects under the sound board. If a customer put a piano on top of a heating rad we would be all over them about the placement of the piano. With radiant heat the whole floor is a heating source. If you live in an area that doesn't experience much cold weather then it may be OK but here in the great lakes area it's a problem.

There are surely more threads on this topic, I remember seeing a few...
In my experience, anyone putting a piano on that kind of a floor is asking for trouble. Tuning instability is just the start of it. The next phase can be soundboard and tuning pin torque issues, etc.

You can debate whether it is possible or not until the cows come home, what counts is what is actually happening.

Note: I am not saying bad things "will" happen, I am saying they "may" happen. Just don't be surprised...

In my experience, forced air with a good furnace humidifier beats radiant heat 10 fold. Radiant heat does make a piano very unstable. There will be a measurable change in pitch from winter to summer.

Radiant heat can be bad for pianos. One of my customer newer Baldwin upright developed a crack in the soundboard. I installed a Dampp-Chaser system and the crack closed up. You have to remember you have a constant 90-100 degree heat source and the piano is sitting on it. You are bound to have tuning problems and other issues like crack bridges, soundboard etc. I would always recommend a Dampp-Chaser system in these cases.