# How much heat should I recover from furnace flue gas, and how is the recovery rate calculated?

Canonical: https://senseible.earth/answers/waste-heat-recovery-rate-furnace-flue-gas

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.

- [Recuperator fuel savings](https://senseible.earth/answers/recuperator-combustion-air-preheat-fuel-saving)
- [Boiler economiser fuel saving](https://senseible.earth/answers/boiler-economiser-fuel-saving)
- [Which scope is waste heat power](https://senseible.earth/answers/waste-heat-recovery-power-which-scope)

Sources: [BEE, Energy Conservation Guidelines for MSME Sector (2019): Tables 6.9, 6.23, 6.40, 6.67 and 6.72, with the waste heat recovery rate formula](https://beeindia.gov.in/WriteReadData/L45218/1734411984.pdf)

Last reviewed 2026-10-24.