How to recognise good wood pellets before you burn a whole pallet

First, something most guides skip: judging "by eye" is a supplement to a certificate, not a replacement for it. As the trade magazine Magazyn Biomasa concedes, certainty about pellet quality comes only from laboratory tests — and home tests are viewed sceptically by some experts. They're still worth knowing, because they catch the grossest problems: a damp batch, one overloaded with fines, or one that doesn't match what the label promises.

Order matters. First what you check before paying, then what you check on delivery, and home tests last.

Before buying: the label and the paperwork

This is the filter that screens out the most — and needs no bag opened:

1. Class stated explicitly. A1, A2 or B — with the standard's specific thresholds (for A1: ash ≤ 0.70%, durability ≥ 98%). What they mean is in A1 vs A2. If the seller states no class anywhere — not on the bag, not on the page — you don't know what you're buying. In our price table we mark such offers as unknown class for precisely that reason.
2. A certificate number, not just the logo. The ENplus or DINplus mark can be printed; a number in the certifying body's database can't. How to verify it in three steps: ENplus and DINplus certificates.
3. Weight and price you can convert. An honest offer states the bag and pallet weight, so zł/t can be computed. An offer where you can't establish how many kilograms you're paying for is a warning sign in itself.

On delivery: what the naked eye can see

Here the ENplus standard translates into specifics, because some of its thresholds are visible without a laboratory:

• Fines at the bottom of the bag. The standard permits at most 0.5% fines in bags. A bag with a distinct layer of sawdust and dust at the bottom means pellets that crumbled in transport or were weak from the start — and fines clog the auger and worsen combustion.
• Pellet surface. A good pellet is smooth, hard and slightly glossy; it snaps with a crack rather than crumbling in your fingers.
• Length. The standard requires pellets of 3.15–40 mm. A batch full of very short fragments is again a sign of crumbling.
• Colour and smell. A uniform wood shade (varying by species — a darker colour alone doesn't disqualify) and the smell of wood, not chemicals or mustiness. Mustiness points to damp — what to do with such goods is in the storage article.

If a batch looks bad right on delivery — photos and a complaint before using the goods, not after.

The glass-of-water test — what it really shows

The most popular home test: a few pellets into a glass of water.

What to look for: a good pellet should quickly sink to the bottom — a sign of proper compaction. Left longer in water it will disintegrate into a pulp of wood fibres; that's normal, because good pellets are bound by lignin, wood's natural binder, not by glues. A floating pellet indicates too little compaction or dampness.

What this test does NOT show — and this is the more important half: it says nothing about ash content, calorific value or whether the fuel meets the standard. Magazyn Biomasa, describing the test, states plainly that only laboratory testing gives certainty — and some experts consider home tests unserious for certified pellets. So treat the glass as a quick detector of an obviously bad batch, not as proof that a batch is good.

The most reliable "test": the boiler's behaviour

Paradoxically the best home diagnostic is the boiler itself, watched for a few days on a new batch: how much ash is left in the pan compared with the previous fuel, whether the ash fuses into hard lumps (we noted under classes that the standard requires an ash deformation temperature of ≥ 1200°C for A1), whether the feeder runs smoothly and whether the boiler room smells of burning wood rather than something sharp. That's why with an unknown brand it's sensible to buy a bag or two first rather than pallets straight away — the same conclusion the arithmetic in bags or pallet leads to.

Summary

The order of defence against bad pellets: certificate with a number → inspection on delivery → a trial batch in the boiler. Home tests we leave for last, because that's how much they weigh. And once you know a given brand works for you — the rest of the difference is price, and that's where our table begins.

Sources

• Magazyn Biomasa — "Pellet w szklance wody – czy ten test działa naprawdę?" — mechanics of the water test, its limitations and the caveat that only laboratory tests give certainty (Polish).
• ENplus® ST 1001:2022 — ENplus® wood pellets: Requirements for companies (Bioenergy Europe / DEPI), Annex A, Table 4 — thresholds for fines (≤ 0.5% in bags), length (3.15–40 mm), mechanical durability and ash deformation temperature cited in the text.