How to choose pellets for your boiler: ENplus class, ash content, diameter, testing

Wood pellets or agro pellets

The first fork in the road is the raw material. Wood pellets are pressed from softwood or hardwood sawdust; their ash content is below one per cent, and they are the ones suited to domestic pellet boilers with a small ash pan. Agro pellets are made from sunflower husk, straw or other plant material: a tonne costs noticeably less and the calorific value is only a few per cent lower, but there is 3-5 times more ash and it tends to sinter. Agro pellets make sense in boiler houses with mechanised ash removal and in boilers whose manufacturer explicitly permits agro fuel. For a home boiler without such a note in its manual, use wood pellets only.

What ENplus A1 and A2 mean

ENplus is the European certification scheme for wood pellets, which sets standards for the raw material, ash content, moisture, durability, fines content and even logistics. Two classes matter to the buyer.

Parameter	ENplus A1	ENplus A2	Industrial (B, unclassified)
Raw material	stem wood without bark	stem wood, residues with bark	any wood
Ash content	up to 0.7%	up to 1.2%	up to 2% or more
Moisture	up to 10%	up to 10%	up to 10-15%
Mechanical durability	from 98%	from 97.5%	not specified
Fines (dust) in the bag	up to 1%	up to 1%	not specified
Suitable boiler	domestic with a small ash pan	domestic with a larger ash pan, boiler houses	industrial boilers

For most home boilers, the difference between A1 and A2 is how often you clean: with A2 you will empty the ash pan roughly twice as often, but the tonne is cheaper. If the boiler has automatic ash removal or a large ash pan, A2 is a sensible saving. If the burner is small and prone to sintering, choose A1.

An important detail: an ENplus certificate is issued to a specific producer or trader and carries a number such as UA 001. The words "ENplus A1" on a bag without a number or a certificate are marketing, not a class. The number can be checked in the public register on the ENplus website. We provide the documents for each batch together with the delivery note; if there is no certificate for a particular batch, we say so on the product page instead of assigning a class at random.

Diameter: 6 or 8 mm

Almost all domestic pellet boilers and burners in Ukraine are designed for 6 mm pellets. The 8 mm diameter is found in industrial boilers and some older models. An 8 mm pellet in an auger designed for 6 mm feeds unevenly and jams; a 6 mm pellet in a boiler designed for 8 mm usually works fine, although the feed rate will be slightly different. Check the boiler manual: it always states the diameter and often the maximum pellet length (usually up to 40 mm).

Pine or oak

Softwood pellets (pine, spruce) are the most common and usually the cheapest wood pellets. Thanks to the resin their calorific value is even slightly higher, they leave less ash and they are light in colour. Hardwood pellets (oak, ash, beech) are denser and burn longer, but leave slightly more ash and cost more. For the boiler the difference is not essential, so choose by price per tonne and availability. It is worse when bark gets into the sawdust: the pellets darken, the ash content rises and the burner clogs faster. A uniform light colour is a good sign.

How to test pellets without a laboratory

The bag. Intact and dry, with the producer's markings; no more than a handful of sawdust at the bottom. If there is a finger-thick layer of dust at the bottom, the pellets are brittle or the bags were stored carelessly.

The surface. Smooth, glossy, without cracks or "tails". A matt, rough pellet is a sign of weak pressing.

The snap test. A pellet is hard to break with your fingers; dropped from table height, it does not crumble into sawdust.

The water test. In a glass of water, good pellets sink and break down into uniform sawdust within 5-10 minutes. If they float, the density is low; if the water turns oily or develops a film, binders have been added.

The smell. Fresh wood, with no chemical notes. A sharp smell indicates glue or treated wood, and such raw material is not allowed in pellets.

The burn test. Put a few pellets on a metal plate: they should burn with an even flame and leave a pinch of light ash. A black sticky mass instead of ash means high ash content or sintering, and such pellets are not suitable for a home boiler.

Documents worth asking for

At a minimum, a quality certificate for the batch with four figures: ash content, moisture, calorific value and mechanical durability. If the seller claims ENplus, the certificate number. For a boiler house buying by the railcar, also a test report from an accredited laboratory. At Thermera the certificate comes with the delivery note; we fill in the specifications on product pages only after we receive the document for the batch, so an empty "Ash content" field on the website means "the batch has not been tested yet", not "we forgot".

How much to buy and how to store it

An insulated house of 100-150 m² uses 3-5 tonnes of wood pellets per season, which is 3-5 pallets of 65-70 bags. A 15 kg bag is convenient for topping up the hopper every day; big bags and bulk loads suit boiler houses with storage and auger feed. Keep pellets dry: they absorb moisture from the air, swell and crumble. Store bags on a pallet under a canopy or indoors, and big bags only under a roof. In these conditions pellets keep for several seasons without any loss.