It's control: seasonal air density, fuel variation and load swings move the optimum daily — trim follows it automatically.
From our guide: Burner tuning & O2 trim — full context, charts and sources there.
Boilers, kilns, heat exchangers, valves and steam lines lose energy continuously. Inzonex makes patented (UK GB2508992.1) removable modular insulation — snap-fastened covers engineered per temperature tier, not generic off-the-shelf jackets: