# How much wood does an economiser on a thermic fluid heater save?

Canonical: https://senseible.earth/answers/thermic-fluid-heater-economiser-wood-saving

Thirty tonnes of wood a year in BEE's Solapur report, about a fifth of a dyeing unit's 144 t, by cooling heater flue gas from 360 C to 120 C to make process hot water. Cost Rs 1.29 lakh, payback 1.7 years at Rs 2,500 a tonne (2010). Size it to your hot water use first.

## The heater in the report

- Thermic fluid heater of 3 lakh kcal an hour, fired on wood of about 3,200 kcal a kg, 8 hours a day, 240 days a year.
- Efficiency 35 to 45%. Flue gas leaves at 330 to 360 C and carries 33 to 38% of the heat.
- The unit burns 144 t of wood a year for 288 t of product.
- Proposed: a shell and tube economiser in the flue, rated 2,500 litres a day, heating process water to 55 to 60 C, with flue gas leaving at about 120 C.

## Check the 30 tonnes against your water

Heating 2,500 litres a day from 27 C to 55 C takes about 70,000 kcal. At the heater's 35 to 45% efficiency that replaces about 49 to 63 kg of wood a day, roughly 12 to 15 t a year. The report's 30 t needs about 5,000 to 6,400 litres of hot water a day from the economiser. If you use only 2,500 litres, expect the smaller saving and a payback nearer 4 years.

## Cost and fitting

- Rs 1.25 lakh for the economiser, insulation, piping and tank; Rs 1.29 lakh in all.
- About 2 days to fit; it can be done on a weekly holiday.
- Saving in the report: 30 t x Rs 2,500 = Rs 0.75 lakh a year.

## What it does to your carbon figures

- Fossil CO2: no change; the saving is wood
- Wood saved: 30 t x 3,200 kcal/kg x 4.1868 = about 402 GJ
- Biogenic CO2 avoided: 402 GJ x 112 kg = about 45 t
- The report's 42 t used 1.4 t CO2 a tonne of wood
- Wood per kg of product: 0.50 kg falls to about 0.40 kg

Wood CO2 uses the IPCC 2006 default of 112 kg CO2 a GJ with the report's calorific value. It is biogenic and reported separately, outside Scopes 1 to 3.

## What Senseible does here

Senseible reads your electricity bills into records with CO2. It has no factor for wood, so keep wood tonnes from purchase bills as a separate biogenic line; the green loan check shows what a lender asks for on heat recovery.

- [Green loan readiness check](https://senseible.earth/green-loan-check)
- [Solapur textiles: wood fuel and carbon](https://senseible.earth/answers/solapur-textile-cluster-wood-fuel-carbon)
- [Thermic fluid heater emissions](https://senseible.earth/answers/thermic-fluid-heater-emissions-scope-1)
- [Efficient wood hot water generator](https://senseible.earth/answers/efficient-hot-water-generator-wood-saving)

Sources: [BEE, Detailed project report: waste heat recovery through economizer, 2,500 LPD, Solapur textile cluster (2010, SAMEEEKSHA)](https://sameeeksha.org/pdf/dpr/fluid_heater.pdf), [IPCC 2006 Guidelines, Volume 2 Energy, Tables 1.2 and 2.3](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html), [GHG Protocol Corporate Standard (biogenic CO2 reported separately)](https://ghgprotocol.org/corporate-standard)

Last reviewed 2026-10-31. Report figures are from a BEE SME programme project report; costs and paybacks are at 2010 prices. Check today's wood price and your own hot water use.