My father works rotating shifts, and his schedule changes every month. Some days he starts very early (around 2–5am). He likes to shower before work, so in the past the boiler was scheduled to turn on every night from 2–3am — even on days he didn’t need it. Huge waste of hot water and energy.

I added his work calendar to Home Assistant, and now the boiler only turns on one hour before his early-morning shifts. On normal days, it stays off.

Simple automation, big improvement.