Gas-fired: ~2–3% at high fire. Higher = excess air = loss; lower risks CO. Trim control holds the line as conditions vary.
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: