How to Check Wood Pellet Quality: 5 Home Tests

Updated: 14 August 2026 · Timo Pellets, wood pellet producer, Certeju de Sus, Romania · Citește în română

In short: you can assess pellet quality at home in minutes with five checks: the water test (good pellets sink), the drop test (they should not shatter), the dust check at the bottom of the bag, appearance and smell, and the ash volume after a few days of burning. On the packaging, the numbers that matter are those defined by ISO 17225-2: moisture ≤ 10%, ash ≤ 0.7% and calorific value ≥ 4.8 kWh/kg for premium class A1.

Five tests you can do at home

1. The water test (density)

Drop 5–10 pellets into a glass of water. Well-compressed pellets with a density above 1,100 kg/m³ sink immediately and resist disintegration. Those that float and fall apart within seconds have low density and usually higher moisture — they will burn faster and deliver less heat.

Note: the reverse version of this test circulates online ("if they float, they are premium"). It is wrong. High density is always a good sign in pellets.

2. The drop test (mechanical durability)

Take a handful of pellets and drop them from about one metre onto a hard surface. Quality pellets stay whole or break into large pieces. If they shatter into dust, mechanical durability is below standard — and that dust turns directly into ash and clogs the feed system.

3. Dust in the bag

Open the bag and look at the bottom. A visible layer of fine sawdust means poor pressing or rough handling. The standard limits fines to a maximum of 1% for class A1.

4. Appearance, smell and uniformity

Good pellets have a smooth, slightly glossy surface — a sign that the sawdust was pressed at the right temperature and the wood's own lignin acted as a natural binder. Colour should be uniform. Very uneven lengths, longitudinal cracks, pieces of plastic or paint and any chemical smell are red flags.

5. Ash after a few days of burning

This is the most honest test, because it measures the actual result. With class A1 pellets, ash removal is typically needed every 5–7 days of operation. If you must clean every 2–3 days, ash content is well above 0.7%.

What ISO 17225-2 actually means

ISO 17225-2 is the international standard defining quality classes for wood pellets intended for non-industrial use. It is not a commercial logo but a set of measurable, laboratory-verifiable limits.

Parameter	Class A1	Class A2	Class B
Diameter	6 or 8 mm	6 or 8 mm	6 or 8 mm
Length	3.15–40 mm	3.15–40 mm	3.15–40 mm
Moisture	≤ 10%	≤ 10%	≤ 10%
Ash	≤ 0.7%	≤ 1.2%	≤ 2.0%
Calorific value	≥ 4.6 kWh/kg	≥ 4.6 kWh/kg	≥ 4.6 kWh/kg
Mechanical durability	≥ 97.5%	≥ 97.5%	≥ 96.5%
Raw material	Natural wood, no chemically treated wood	Natural wood, bark tolerated	May include untreated recycled wood

Why these numbers matter to you

For your wallet: the gap between class A1 and an uncertified product shows up directly in consumption. High-moisture, low-density pellets can require 20–30% more fuel for the same indoor temperature.

For your boiler: excess ash, dust and impurities clog the feed auger, foul the heat exchanger and accelerate wear. Many boiler manufacturers make their warranty conditional on using certified-class pellets.

For health and environment: pellets made from chemically treated wood, chipboard or furniture waste release compounds that have no place in a home's flue.

How to verify a producer's claims

Ask for the laboratory report. A serious producer can present test results for moisture, ash and calorific value. It is the most direct test of credibility.
Check certification codes. ENplus and FSC assign individual codes, each belonging to a single company, published in online registers. A code printed on a bag can be verified in seconds.
Read the packaging. The absence of technical specifications is itself information.
Buy one trial bag first. Test it using the methods above before ordering a tonne or a pallet.

Timo Pellets products are made exclusively from natural hardwood — beech, oak, hornbeam, ash and black locust — with no additives and no binder, manufactured to the ISO 17225-2 class A1 specification. Full specifications are printed on every bag.

Frequently asked questions

Do good wood pellets float or sink in water?

Good quality pellets, well compressed and dense, sink. Those that float and disintegrate quickly have low density and higher moisture. Note that the opposite version of this test circulates online and is incorrect — quality pellet density exceeds 1,100 kg/m³, so they settle to the bottom.

What does ISO 17225-2 mean?

It is the international standard defining quality classes for wood pellets. It sets limits for diameter, length, moisture, ash content, mechanical durability, fines and calorific value, dividing pellets into classes A1, A2 and B.

How often should I empty the ash if the pellets are good?

With class A1 pellets (ash below 0.7%), ash removal is typically needed every 5–7 days of continuous operation. Having to clean every 2–3 days is a clear sign of high ash content.

How do I verify a producer's certification claims?

ENplus and FSC certifications carry individual codes that are publicly verifiable in the organisations' online registers. You can look up the code shown on the bag and immediately see which company it belongs to. A declaration of conformity with ISO 17225-2 is a producer's declaration, backed by laboratory test reports you can request.

Premium pellets, direct from the producer

Timo Pellets produces hardwood pellets (beech, oak, hornbeam, ash, black locust) in Certeju de Sus, Hunedoara County, Romania. Delivery across Romania and internationally.

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