I read two posts about use of Dampp Chaser systems in pianos and
all I can say is that I highly support their use in pianos based on
personal experience as a professional piano technician.  I live on
the East Coast near the ocean and have seen the tremendous damage
that can be done from high humidity: mold, mildew, rust, sticking
actions, swollen keys, cracked soundboards, etc.  I have yet to see
a piano damaged by such systems although I will say the systems that
have no humidistats are a hazard due to the danger of over-drying.
Improper installs can cause problems which is one of the reasons
there now is a certified installer program.  Whole house systems are
expensive and room dehumidifiers have to be emptied and are noisy.  The
bottom line is the Dampp Chaser systems work and they are not a scam.

James Kelly