I agree with MusicDiva,
The piano we had in our living room when I was growing up, my mom would always have it tuned twice a year. The worst things for acoustic piano's is moving them, varying tempature and humidity differentals. Most professional rock bands like Elton John and the Rolling Stones always carried there own personal piano tuners when they were touring, and he would have to tune the piano's before the show started. But for home 2x a year is fine.