One of the biggest factors in the piano's ability to stay in tune is humidity.  The action in a piano is also affected greatly by changes in humidity.  A piano's humidity can be controlled by the use of a humidity control system. Although a humidifier system will not take the place of tuning or regulating the piano,  it will help keep the piano more stable between servicing.  For more information about this system, go to

Humidity Control
Matt Shoemaker
Piano Tuning and Repair