How to Choose Pellets for Your Home
If you heat a home with pellets, the choice usually isn't between "good" and "bad" pellets — it's about how well a specific batch's declared parameters match your particular boiler or stove. Here's what to check first, and where to find the details on each parameter.
- Equipment type. An automatic pellet boiler or stove with a small ash pan needs low ash content and minimal fines — otherwise the burner clogs more often than the manufacturer intended. A stove or boiler with manual feeding and a large ash pan is far less sensitive to these.
- Certification class. For sensitive equipment, the benchmark is ENplus A1 or DINplus; see the pellet certification page for how classes A1/A2/B differ.
- Storage and delivery conditions. Even good pellets lose their properties if stored badly — see moisture and mechanical durability below.
- Storage volume. If space is limited, check bulk density — it determines how much energy fits into your available silo or storage room.
- Heating cost. Compare price per unit of heat, not just price per kilogram or bag — see calorific value.
A detailed breakdown of each parameter — what it means, what it affects, and what to look for — follows below.
Ash Content
What it is. The share of incombustible mineral residue (ash) left after pellets burn completely, as a percentage of dry mass. It underlies the EN ISO 17225-2 classes: A1 — ≤0.7%, A2 — ≤1.2%, B — ≤2.0% (see the class table on the certification page).
What it affects. Higher ash content means more frequent cleaning of the ash pan and burner, and a higher risk of clinker — fused ash that can clog a modern automatic boiler's burner and trigger a fault shutdown.
What to look for. For automatic boilers and stoves cleaned infrequently, class A1 pellets (ash ≤0.7%) are the better choice; a stove or boiler with manual feeding and a large ash pan can work fine with A2/B. Low ash content almost always goes hand in hand with cleaner raw material — free of bark and foreign matter.
Moisture
What it is. The share of water in a pellet's mass, normally brought down to ≤10% by the producer during drying and pressing.
What it affects. Water in a pellet has to evaporate before the wood can burn properly — part of the combustion energy goes into that, so wetter pellets give off less heat per kilogram (see calorific value), ignite less readily, and produce more smoke from incomplete combustion. In storage, overly moist pellets swell, crumble, and can go moldy.
What to look for. The standard across A1/A2/B is moisture no higher than 10%, but even certified pellets pick up moisture if stored somewhere damp and poorly ventilated. Pellets that feel damp, crumble easily, or smell musty are a red flag regardless of the stated class.
Mechanical Durability
What it is. The share of a pellet's mass that stays intact after a standardized abrasion/tumbling test — in other words, how well pellets hold together during transport and handling instead of breaking into crumbs and dust. Requirements: A1 — ≥98.0%, A2/B — ≥97.5%.
What it affects. Low mechanical durability means part of the batch turns to dust during transport, unloading, and auger feeding into the burner — increasing fines, clogging feed augers and sensors, and hurting combustion quality.
What to look for. Higher is better, but in practice it's hard to verify yourself beyond the stated certification class. Visible dust and crumbs at the bottom of a bag or silo after delivery is an indirect sign of low durability.
Fines
What it is. The share of particles smaller than 3.15 mm (crumbs and dust) in a batch, measured by sieving. The limit is the same across A1/A2/B — no more than 1.0%.
What it affects. Fines and dust are a fire and dust-exposure risk during storage and loading, clog feed augers and level sensors, and burn faster and hotter than a whole pellet — complicating the work of automatic boiler controls tuned for steady combustion.
What to look for. The share of fines is directly tied to a batch's mechanical durability and how carefully it was transported — visible dust in the bag or at the bottom of a silo signals a problem even if the packaging claims a premium class.
Calorific Value
What it is. The amount of heat energy released when one kilogram of pellets burns completely (net calorific value), measured in MJ/kg. EN ISO 17225-2 sets 16.5–19.0 MJ/kg for A1/A2 and 16.0–19.0 MJ/kg for B.
What it affects. The higher the calorific value, the fewer kilograms of pellets you need to burn for the same amount of heat — directly lowering how fast the silo empties and how often you need to restock over a heating season.
What to look for. When comparing sellers, it's worth working out price per unit of heat rather than just price per kilogram or bag — pellets that cost slightly more per kg but have a higher calorific value can end up cheaper overall. Calorific value is closely tied to moisture: drier pellets give off more heat.
Bulk Density
What it is. The mass of pellets loosely poured into a container of known volume, per unit of volume (kg/m³) — not to be confused with the density of a single pellet's material. The standard range is 600–750 kg/m³.
What it affects. Higher bulk density fits more energy into the same silo, storage room, or bag volume — reducing storage-space requirements and affecting delivery logistics, since a load of denser pellets delivers more heat energy per trip.
What to look for. If storage space is limited, favor pellets near the top of the range (700–750 kg/m³). Noticeably low bulk density can also indirectly point to looser raw material or higher moisture.
Raw Material
What it is. The wood species and condition pellets are pressed from: clean stem wood without bark (class A1), wood where bark is allowed (A2), or partially reprocessed and industrial wood (class B).
What it affects. Bark and foreign matter (sand, soil picked up during harvesting) raise ash content and change its composition, and can also affect smoke odor and combustion cleanliness. Raw material underlies the EN ISO 17225-2 classification and is what wood-origin certificates like FSC and PEFC additionally confirm (see the certification page) — but that's about sustainable sourcing, not the pellet's physical properties.
What to look for. For a stove or boiler where clean burning and minimal ash matter, clean, bark-free wood (A1) is the better choice. For a larger or less sensitive boiler, A2/B raw material isn't a shortcoming — it's often a more affordable alternative.