This page covers potential and economics; the heat-recovery-systems guide covers technology selection by temperature band (economizers, recuperators, heat pumps, ORC).
From our guide: Waste Heat Recovery — 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: