Scotty Greene of DeBence Museum in Franklin, Pennsylvania, asks about
the effects of temperature on tuning.  As a tuner for many years,
I can tell you organ pipes are much more sensitive to temperature than
pianos.  The biggest culprit is the percentage of relative humidity.

The artificial heat of winter can reduce the percentage of humidity.
When humidity levels drop, piano frames and sound boards can shrink.
When they shrink, the tension on the piano strings is lessened and the
pianos tend to go flat in some areas along the scale.  Each piano
shrinks differently -- it depends upon the construction of the piano.

Changing humidity also can also change the pitch of organ pipes, but
organ pipes are more sensitive to changes in temperature.  The air
temperature going through the pipes can be much different than the
temperature within the organ chambers.  Often blowers are located in
basements or attics which are not heated, or are over-heated in summer.
Sometimes the churning of air within the blower can increase in
temperature.

The best way to keep an instrument in tune is to monitor the percentage
of humidity and temperature, and keep it as constant as possible (i.e.,
in a climate-controlled room).

In my home, the percentage of relative humidity in summer can reach
85 percent, but in winter the artificial heat of the heating system
can reduce the percentage of humidity to as low as 20 percent.  This
drastic change causes the tuning of the piano to shift dramatically.

To compensate, the piano is stored in a room that is closely
monitored by a hygrometer and a de-humidifier is used during summer
when artificial heat is not required.  If the summer heat is excessive,
I add air conditioning.  Since my house is very old, adding extra
humidity in winter can damage the construction of the house, especially
in the attic and rooms that are not heated.  Therefore I cannot add
humidity to the house in winter without severe consequences.

I learned this the hard way.  When humidifiers became popular, I raised
the humidity in winter to that of summer.  Great, I thought ... until
the plaster ceiling in my upstairs hall collapsed.  This occurred
because of the excess moisture condensing on the cool surfaces.  Mold
and mildew appeared on windows in unheated rooms.

The only option was to encase the piano in plastic sheeting and place
containers of water inside _and_ behind the piano and monitor the
temperature and humidity under the plastic cover.  It is unwise to
humidify or de-humidify only one side of the piano sound board and not
the other.  It should be equal.

Bruce Clark