By the UK Wood Gasifier Hub – Off-Grid Power & Biomass Energy Guides Team · Updated May 2026 · Independent, reader-supported

Wood Gasifier Fuel Guide UK: Best Wood Types, Moisture Content & Chip Size

A wood gasifier will only perform well if you feed it the right fuel. Too much moisture, wrong wood species, or inconsistent chip size and you'll struggle with tar buildup, poor gas yield, and unreliable operation. This guide covers what actually works in UK conditions.

Why Fuel Quality Matters

Wood gasifiers convert solid biomass into combustible gas through a chemical process that requires precise feedstock conditions. Unlike a simple wood stove where you can burn whatever you find, a gasifier is fussy about what goes in. Get it wrong and you're dealing with restricted gas flow, tar condensation in pipes, and an engine that struggles to run cleanly. Fuel quality directly affects your overall system efficiency, maintenance intervals, and whether the system is even worth your time.

Moisture Content: The Critical Factor

Moisture is the single biggest variable affecting gasifier performance. This needs to be between 10–15% for optimal operation, measured on a dry-weight basis. Anything wetter and the gasifier wastes energy evaporating water rather than gasifying wood. The gas yield drops, tar production increases, and your engine runs lean and rough.

Measuring moisture properly matters. A basic moisture meter (the pin-type ones) costs £20–40 and is essential kit. More accurate are digital meters with conductivity probes, around £60–120. Don't guess—if you're investing in a gasifier, invest in a meter.

In the UK, freshly felled or recently split wood runs 40–60% moisture. You need to season it. Split wood dries faster than logs; a roughly split metre-long piece needs 12–18 months of open-air drying in a covered stack. If you're serious about year-round operation, you'll need two or three seasons of stock drying simultaneously.

Overdried wood (below 10%) isn't a disaster—it gasifies perfectly well—but storing it can be fiddly. The main downside is wood shrinks as it dries, so very dry stored material develops cracks and dust.

Wood Species: Hardwoods vs Softwoods

UK hardwoods are ideal: oak, ash, beech, hornbeam, and sycamore all gasify well. They're dense, have lower resin content, and produce stable, relatively clean gas. Ash is particularly good—it's local, splits easily, seasons quickly, and produces consistent results. Oak takes longer to season but is excellent once ready.

Avoid softwoods like pine, spruce, and larch. These contain high resin content that condenses as tar inside your system. Tar clogs pipes, corrodes engine valves, and requires constant cleaning. If you have no choice, you'll need robust tar-removal equipment downstream, which complicates the whole setup.

Avoid treated or painted wood entirely—chemically treated timber releases toxic compounds, and paint adds unknowns. Likewise, avoid plywood, MDF, and chipboard: the adhesives release formaldehyde and other nasties when gasified.

Softwoods and confiers from forestry waste (thinnings, offcuts) are sometimes available cheaply. Technically they work, but the tar hassle usually isn't worth the saving.

Chip Size and Preparation

Most UK gasifiers run best on chips roughly 10–25mm long and 5–10mm thick. This is a balance: larger chips gasify more completely but create air pockets and uneven flow; smaller chips increase surface area but compact and restrict airflow, especially if they're at all moist.

If you're buying pre-chipped wood (garden waste sites, tree surgeons), sort out the fines. Particles smaller than 3mm pack together, restrict flow, and shouldn't make up more than 10–15% of your feedstock.

If you're making your own chips, a basic petrol-driven wood chipper (£300–600) handles logs up to 80–100mm diameter. Hydraulic options exist but cost significantly more. An alternative is a large log splitter to produce split logs roughly 40–50mm square, which gasifies acceptably though not quite as efficiently as chips.

Whatever method you choose, it has to be dry before chipping. Chipping wet wood clogs the chipper and produces wet chips that won't gasify properly. This is worth stressing: dry first, chip second.

Seasonal Availability in the UK

Winter storms drop plenty of timber, but much of it's absorbed by conventional boiler and biomass plant operators. Summer is when you're most likely to find reasonably priced dried stock at garden centres and agricultural suppliers. Plan ahead: build your dry-wood reserve in summer and autumn, so you're not caught short when demand peaks.

Storage and Handling

Stack wood in a covered area where air can circulate but rain doesn't soak it. Direct ground contact invites moisture ingress and rot; ideally, stack on a gravel or concrete base. For longer-term storage, tarping the top but leaving the sides open works well in UK conditions.

Once chipped, the material is more prone to reabsorbing moisture and to insect activity. If you're making chips months ahead, store in breathable sacks (hessian or polypropylene mesh) in a dry shed rather than loose piles.

Common Mistakes

• Burning fresh wood. Most people's first attempt fails because they're burning wood that's 30+ % moisture. It won't work. Season first.
• Inconsistent particle size. A mix of dust-fine material and chunks larger than your system is designed for causes bridging and poor gas quality. Screening out fines and aiming for consistent sizing saves weeks of troubleshooting.
• Storage in damp sheds. If your storage space isn't drier than the wood you put in, your fuel quality won't improve. Proper ventilation and shelter are essential.

Summary

Feed your gasifier well-seasoned (10–15% moisture), properly sized hardwood chips, and it will run reliably. Cut corners on fuel prep and you'll spend half your time unblocking pipes and replacing engine components. The difference between success and frustration often comes down to fuel, not the gasifier itself.