Wood shifts with humidity, and so your guitar will subtly adjust and this can throw your tuning off. Your HVAC could be causing major humidity shifts that your guitar doesn’t like. Check to see whether the room that you keep your guitar in has significant humidity shifts by purchasing a hygrometer. You can find digital hygrometers online for around $10 to $20. You should keep the room where you guitar is stored in the 40 to 60% humidity range. If you see fluctuations outside this range, get either a humidifier, dehumidifier, or both.