# How much furnace oil does an air preheater save on a galvanizing or annealing furnace?

Canonical: https://senseible.earth/answers/galvanizing-furnace-air-preheater-oil-saving

Close to one litre in twenty, 4.8%, in BEE's Howrah report: 5,647 litres a year out of 118,080, by cooling flue gas from 490 C to 380 C and heating combustion air with it. That is about 17 t CO2. Cost Rs 2.49 lakh, payback 1.47 years (2010), but the report gives the unit only a 3 year life.

## What BEE measured

- Furnaces in the cluster dump flue gas at 490 to 600 C; the audited furnace at about 470 to 490 C, with 4.5% oxygen.
- A typical unit burns 118,080 litres of furnace oil a year at Rs 30 a litre.
- The air preheater takes flue gas in at 490 C and lets it out at 380 C, a 110 C drop.
- Installation needs about 4 days of downtime to change the flue line.

## How the 4.78% was worked out

The report uses a rule of thumb: each 23 C taken out of the flue gas improves efficiency by 1%. 110 / 23 = 4.78%, applied to the oil bill. It is an estimate, not a measured trial. Your saving depends on how much air the preheater actually warms and how airtight it stays.

## The 3 year life changes the sums

- Cost: Rs 1.80 lakh for the unit, Rs 0.40 lakh to install, Rs 0.29 lakh taxes and freight.
- Saving: about Rs 1.69 lakh a year at 2010 oil prices.
- Over the 3 year life the report assumes: about Rs 5.1 lakh saved for Rs 2.49 lakh spent.
- Ask the supplier why the life is 3 years and what a replacement costs.

## Keep it working

- Check for leaks between the flue side and the air side; leaking flue gas into the burner air cancels the saving.
- Log flue temperature after the preheater weekly. If it creeps up, the surfaces are fouling.
- Keep oil litres and tonnes galvanized in the same monthly log, so oil per tonne can be compared.

## One furnace, one year

- Oil before: 118,080 L x 2.97 = 350.7 t CO2
- Oil saved: 118,080 x 4.78% = 5,647 L
- CO2 saved: 5,647 x 2.97 = 16.8 t a year
- Report says 18 t; the difference is the oil factor used

Furnace oil at our factor of 2.97 kg CO2 per litre, an estimate.

## What Senseible does here

Senseible reads furnace oil invoices into monthly records with CO2 at 2.97 kg per litre, so a 5% drop in oil per month is visible once the preheater is in. The green loan check shows what a lender will want to see.

- [Green loan readiness check](https://senseible.earth/green-loan-check)
- [Galvanizing energy per tonne benchmark](https://senseible.earth/answers/galvanizing-plant-energy-per-tonne-benchmark)
- [Howrah galvanizers and CBAM](https://senseible.earth/answers/howrah-galvanizing-wire-units-cbam-carbon)
- [Coal galvanizing furnace to biomass gasifier](https://senseible.earth/answers/galvanizing-coal-furnace-to-biomass-gasifier)

Sources: [BEE, Detailed project report: air pre-heater for galvanizing and annealing furnaces, Howrah cluster (2010, SAMEEEKSHA)](https://sameeeksha.org/pdf/Howrah_galvinising/DPR_on_Air_Pre_Heater_for_galvanizing_and_annealing_furnace.pdf)

Last reviewed 2026-10-31. Equipment figures are from a BEE SME programme project report; costs and paybacks are at that report's prices. Recheck with today's fuel and power prices and a current quote.