Why does the Surat manual measure a boiler at 36.3% but cost the new boiler against 60%?

The Bureau of Energy Efficiency (BEE) Surat manual measures a boiler at 36.3% efficiency, then costs a new 75% boiler against an old one at 60%. That prints 1,500 tonnes and rupees (Rs) 33.0 lakh a year; from 36.3% the same sums give about 3,790 tonnes and Rs 83.4 lakh.

The two tables

• Boiler performance table: 5,000 kilograms (kg) an hour boiler making 2,000 kg of steam, burning 850 kg of fuel an hour at 4,000 kilocalories (kcal) a kg. Heat in 3,400,000 kcal an hour, heat out 1,234,200, efficiency 36.3%.
• Cost table (1 lakh = 100,000): new boiler 75%, present boiler 60%, fuel saving 21%, present use 7,344 tonnes a year, saving 1,500 tonnes, Rs 33.00 lakh a year at Rs 2,200 a tonne of lignite, investment Rs 32.00 lakh, payback 1.0 year.
• The text before them says boilers of single pass design had efficiencies 'around 40% only' and recommends 75%.

Rebuilding the cost table

850 kg x 24 hours x 360 days = 7,344 tonnes, so present use is the measured boiler's. 1 minus 60/75 = 20%, or 1,469 tonnes, against 21% and 1,500 printed. 1,500 x Rs 2,200 = Rs 33.0 lakh. Payback 32 / 33 = 0.97 years.

From the measured 36.3% instead: 1 minus 36.3/75 = 51.6%, 3,790 tonnes, Rs 83.4 lakh, payback 32 / 83.4 = 0.38 years, about 4.6 months. A lower old efficiency means more fuel for the same steam, so the printed saving is the cautious one.

Why not to take 83.4 either

• The measured boiler runs at 40% of its rating (2,000 of 5,000 kg an hour). The manual blames low efficiency on sub-optimal loading as well as design. A new 5,000 kg an hour boiler on the same load may also part-load.
• 75% is a design figure. The manufacturer table in the manual prints 72 plus or minus 2 for its 2,000 to 4,000 kg an hour models. At 72% the measured case saves 49.6%.
• The cost table names lignite for price but the cluster total in the text says tonnes of coal. Confirm which fuel you burn.

The cluster line

The text puts the replacement at about 50 units: 75,000 tonnes of coal, Rs 1,650 lakh a year, investment Rs 1,600 lakh, payback 1.00 year. These are 50 times the one-unit lines: 50 x 1,500, 50 x 33.0, 50 x 32. The cluster figure inherits whichever baseline the single unit used.

One unit, two baselines

• Present use: 850 kg x 24 x 360 = 7,344 tonnes
• Costed from 60%: 1 minus 60/75 = 20%, 1,469 tonnes (1,500 printed), 1,500 x 2,200 = Rs 33.0 lakh, payback 0.97 years
• Costed from 36.3%: 1 minus 36.3/75 = 51.6%, 3,790 tonnes, x 2,200 = Rs 83.4 lakh, payback 0.38 years
• 50 units at the printed line: 75,000 tonnes, Rs 1,650 lakh, Rs 1,600 lakh invested

Inputs are the manual's, at its year's prices. The 36.3% rebuild is our arithmetic; it is an upper bound until the maker guarantees efficiency at your load.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so your boiler's fuel tonnes by month are on file, so the baseline is your invoices and not a table. It does not measure boiler efficiency; that needs a flue gas test or a heat balance.

• Surat 3 and 4 tonne boiler reports
• Online flue gas analyser on a coal boiler
• Green loan readiness check

Sources: BEE, Manual on Energy Conservation Measures in Textile Cluster, Surat (SAMEEEKSHA)

Last reviewed 2026-11-06. Figures are the manual's, at its year's prices. Get a current quote and a guaranteed efficiency at your own load before relying on the payback.