# Biomass gasifier or LPG for a small furnace or dryer: which has lower emissions?

Canonical: https://senseible.earth/answers/biomass-gasifier-vs-lpg-furnace-emissions

A biomass gasifier usually has far lower reported Scope 1 emissions than LPG, because the CO2 from burning biomass is biogenic and reported outside the scopes. Only its methane and nitrous oxide count, a small fraction of LPG's CO2. The claim holds only if the biomass is residue or sustainably sourced, and the gasifier's blower power still counts.

## How each fuel is counted

- LPG: 2.98 kg CO2 per kg burnt (IPCC 2006 default), all fossil Scope 1, plus very small CH4 and N2O.
- Biomass through a gasifier: the CO2 from the producer gas flame is biogenic. The GHG Protocol asks you to report it separately, outside Scopes 1, 2 and 3.
- CH4 and N2O from biomass combustion are counted in Scope 1, using IPCC 2006 stationary combustion factors and a named GWP set.
- Electricity for the gasifier blower, feeder and gas cleaning is Scope 2; diesel for a backup DG is Scope 1.

## Compare per unit of useful heat, not per kg

A gasifier system loses more energy between fuel and product than an LPG burner: char, tar and sensible heat in the gas. Work out the biomass needed for the same useful heat using the efficiency of each system, then apply the factors. A lower efficiency raises the biomass tonnage and the CH4 and N2O, but rarely enough to close the gap with LPG.

## When the biomass claim weakens

- Wood cut from land that is not regrowing: buyers and assurers may question a zero fossil figure without evidence of sustainable sourcing.
- Biomass carried long distances by truck: transport diesel belongs in Scope 3 and grows with distance.
- A gasifier running poorly, with high tar and unburnt gas venting, which raises methane.
- A dryer where product quality needs clean heat and LPG is kept as backup; count the LPG you still buy.

## What to keep as evidence

- Biomass purchase invoices with tonnage and type, such as rice husk, wood chips or briquettes.
- Supplier declarations on where the residue or wood came from.
- Moisture content tests, since wet biomass carries less energy per tonne.
- Any LPG still bought, and electricity bills for the gasifier connection.

## Illustrative dryer using 20,000 kg LPG a year

- LPG CO2: 20,000 x 2.98 = 59,600 kg CO2; its CH4 and N2O add about 52 kg CO2e
- LPG energy: 20,000 kg x 47.3 GJ per t = 946 GJ; useful heat at 80% burner efficiency = 757 GJ
- Gasifier at an assumed 60% system efficiency: 757 / 0.60 = 1,261 GJ of biomass, about 81 t of wood at 15.6 GJ per t
- CH4: 1.261 TJ x 30 kg per TJ = 37.8 kg x 28 (AR5 GWP) = 1,060 kg CO2e
- N2O: 1.261 TJ x 4 kg per TJ = 5.0 kg x 265 (AR5 GWP) = 1,337 kg CO2e
- Gasifier Scope 1: about 2,400 kg CO2e, against about 59,650 kg CO2e for LPG; biogenic CO2 of about 141 t reported separately

System efficiencies are assumptions. Calorific values (LPG 47.3 GJ per t, wood 15.6 GJ per t), the wood CO2 factor (112 t per TJ) and CH4 and N2O factors are IPCC 2006 defaults; the wood factors for manufacturing combustion stand in for producer gas. Add Scope 2 for the gasifier's electricity.

## What Senseible does here

Senseible calculates LPG CO2 at 2.98 kg per kg from your purchase invoices and keeps each invoice as the source, so a switch shows up month by month as LPG tonnage falling. Keep the biomass invoices, supplier declarations and the gasifier's electricity bills with the same record.

- [Biomass or waste fuel in a boiler](https://senseible.earth/answers/biomass-or-waste-fuel-in-boiler-scope-1)
- [Morbi coal gasifier vs natural gas](https://senseible.earth/answers/morbi-coal-gasifier-vs-natural-gas-emissions)
- [Biomass fuel supplier evidence](https://senseible.earth/answers/biomass-fuel-supplier-evidence)
- [LPG emission factor](https://senseible.earth/emission-factors/lpg)

Sources: [2006 IPCC Guidelines, Volume 2, Chapter 2, Tables 2.2 to 2.5 (stationary combustion CH4 and N2O factors)](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html), [GHG Protocol Corporate Standard (biogenic CO2 reported outside the scopes)](https://ghgprotocol.org/corporate-standard), [IPCC Fifth Assessment Report, 100-year GWP values (CH4 28, N2O 265)](https://www.ipcc.ch)

Last reviewed 2026-10-18.