How much heat should I recover from furnace flue gas, and how is the recovery rate calculated?
Waste heat recovery rate is the heat recovered divided by the sensible heat in the exhaust gas, times 100. BEE's MSME guidelines expect at least 30% from forging, aluminium and galvanizing furnaces, with targets of 38 to 49%, and flue gas leaving at 250 to 300 °C with natural draft or 150 to 250 °C with induced draft.
Standard and target recovery rates
- Forging furnace, exhaust 600 to 1,000 °C: standard 30%, target 49%
- Heat treatment furnace, exhaust up to 600 °C: standard 30%, target 38%
- Aluminium bulk melting furnace, exhaust 500 to 600 °C: standard 30%, target 49%
- Galvanizing furnace, exhaust up to 600 °C: standard 30%, target 38%
- Glass tank furnace, exhaust 1,200 to 1,300 °C: standard 47%, target 57%
- Glass pot furnace, exhaust 800 to 1,000 °C: standard 37%, target 49%
- Boiler in a chemicals or dye unit, exhaust 400 to 600 °C: standard 22%, target 43%
How BEE set the numbers
The standard assumes the top of the exhaust temperature range and a heat exchanger working at 60% efficiency. The target assumes the bottom of the range and 65% efficiency. Natural draft systems leave flue gas hotter than induced draft ones.
Where to put the heat
- Air preheater or recuperator: heats combustion air with flue gas
- Charge preheater: heats the material going in, such as aluminium scrap, billets or glass cullet
- Economiser on a boiler: heats feedwater
Keep it working
Recovery equipment fouls. BEE asks chemical and dye units to clean and maintain flue path recovery systems every six months to stop scale cutting performance.
What Senseible does here
Senseible reads fuel invoices into monthly totals, so the fuel saved after fitting a recuperator or economiser shows in the record against the months before.
Last reviewed 2026-10-24.