I have tried everything.  Not long ago I posted an article on how
I keep my own piano properly humidified in winter.  The first attempt
was to use an in-room portable humidifier.  It seemed to work well but
soon caused structural damage to my house, including mold and mildew
in the attic, exterior house paint peeling, ice dams on the roof, and
more.

Because of these problems, I have constructed a plastic tent over
the entire piano, and keep pans of water on the floor under the "tent".
I keep a hygrometer inside the tent and I keep an eye on the percentage
of humidity.  I keep it at or close to 35% relative humidity.

In summer the outside percentage of humidity can reach upward toward
90%, therefore I keep the doors and windows closed to the room in which
the piano is kept, and use a de-humidifier, and air conditioning to
keep the humidity close to 35%.  Problems in pianos originate from
drastic changes in humidity.

In regard to commercial humidity control attachments for pianos,
adding humidity to one side of anything made of wood, will eventually
cause it to warp.  Not long ago, on a very hot and humid day in July,
I was asked to tune the piano for a local church.  The outside humidity
was over 80%.  The church windows were open.

When I entered the building, I found a woman pouring water to one of
these devices.  I told her water was not required during the hot and
humid summer.  She responded, "The nice man who sold us the unit told
us to keep in full of water at all times."  I could not get her to
understand, and gave up.

Bruce Clark