Agro pellets: which boilers they suit and which they don't
Agro pellets cost 15-25% less than wood pellets with almost the same calorific value, and that is exactly why every year people try burning them in boilers that were never designed for them. The result is slag, daily cleaning and the verdict "agro pellets are bad". They are not bad; they are made for different equipment.
How agro pellets really differ from wood pellets
The raw material is sunflower husk (less often straw, maize or rapeseed). The difference in calorific value is small: 4.4-4.8 kWh/kg versus 4.7-5.0 for wood pellets. The main difference is the ash. Husk leaves 3-5% ash versus 0.5-1% for wood, that is 30-50 kg per tonne instead of 5-10. And this ash is different: it contains a lot of potassium, which lowers its melting point to 650-750 °C. In the hot zone of an ordinary burner such ash melts and fuses into slag. So the question "can I use agro pellets" is really a question of where the ash goes in your boiler and how hot the combustion zone is.
Where agro pellets work well
Retort (cup) burners with moving or self-cleaning grates. Fuel is fed from below, the ash is pushed over the edge of the cup by fresh fuel, and the moving grate bars break up the crust. This is the normal operating mode for agro fuel in Kotlant, Retra, Heiztechnik, "Mars" and similar boilers in their "agro pellet" versions. Check the boiler's technical passport: it states directly whether husk is allowed.
Industrial boilers with mechanised ash removal. Boiler houses, greenhouses, dryers, farms: an ash auger, a large ash pan, servicing once every day or two. Here agro pellets are the main fuel, and the price difference per tonne across dozens of tonnes a season more than covers the cleaning effort.
Boilers with a grate and manual loading (like those burning briquettes or coal): agro pellets can be added in a 5-10 cm layer on top of a glowing bed, and they burn like small coal. The ash stays on the grate and is shaken off. Not automatic, but economical.
Where agro pellets do not work
Flame burner. The most common type in household pellet boilers and in burners fitted into a standard boiler: fuel burns on a fixed grate, air blows from below, and the ash is supposed to fall through on its own. Husk ash does not fall through: it fuses into a cake on the grate within 3-6 hours, and the burner goes out. The forum complaint "a flame burner is too fussy about pellet quality" is exactly about this. More details in the article "Which pellets for a flame burner".
Pellet stoves and inexpensive imported boilers with a small cup. They are designed for A1 pellets with ash content up to 0.7%; 3-5% ash clogs the cup within a day.
Gravity burners without electricity. There is no fan that could compensate for slag with extra air, and no cleaning mechanism.
A "half wood, half agro" mix in a household burner. It looks like a compromise, but the ash content of the mix is still 2-3%, and the potassium from the husk lowers the melting point of all the ash. It slags almost as much as pure husk.
Compatibility table
| Equipment | Agro pellets | What happens |
|---|---|---|
| Retort burner with moving grate, passport allows agro fuel | yes | normal operation, cleaning every 2-3 days |
| Industrial boiler with mechanised ash removal | yes | main fuel, maximum savings |
| Retort burner without moving grate | with caution | daily cup cleaning, risk of slag in frosty weather |
| Boiler with grate, manual loading | yes, like small coal | no automation, shake the grate |
| Flame burner | no | a cake within 3-6 hours, shutdown |
| Pellet stove, small imported boiler | no | cup clogged within a day |
| Gravity burner without electricity | no | goes out |
Setting up the burner for husk
If your boiler allows agro pellets, three rules cut slagging by half. First, more air and a thinner layer: reduce the feed per cycle by 10-20% and increase the fan so the cup does not turn into a "forge". Second, do not let the bed sit for long in standby mode on the verge of going out: a shorter purge cycle, a shorter pause. Third, regularity: clean the cup on a schedule, not when the burner has gone out, because a thin layer of ash leaves on its own, but a crust does not. And do not keep the flow water temperature at maximum: the hotter the boiler, the hotter the cup.
When the savings are real and when they are not
The maths is simple. Say the price difference per tonne between wood and agro pellets is 20%. The difference in calorific value is 5% against husk. So per kilowatt-hour agro pellets are about 15% cheaper. For a house that burns 4 tonnes a season, that is several thousand hryvnias. The price you pay is cleaning the cup every 2-3 days instead of once a week, plus ash that has to go somewhere (incidentally, it works well on a vegetable garden: potassium and phosphorus). If your boiler allows husk and you live next to it, the savings are real. If the boiler is borderline compatible and you visit your country house once a week, they are not: one shutdown in a frost costs more than the entire difference.
Before you order a big bag, burn a 25 kg trial bag in your own burner. One bag is enough to see how much ash, and what kind, is left in your particular cup. Buy in the Agro pellets section; if the test fails, choose wood pellets.
Questions and answers
Can I burn agro pellets in an ordinary pellet boiler?
It depends on the burner. Retort burners with moving or self-cleaning grates run on husk normally, if the boiler's technical passport allows it. In a flame burner, a pellet stove or a gravity burner without electricity, agro pellets fuse into a cake within 3-6 hours and the burner goes out. Such burners need wood pellets: see the article which pellets for a flame burner.
How much ash do agro pellets produce and what do I do with it?
Sunflower husk leaves 3-5% ash versus 0.5-1% for wood pellets, that is 30-50 kg per tonne instead of 5-10 kg. This ash is rich in potassium and phosphorus, so it makes a good fertiliser for a vegetable garden. But it is the potassium that lowers the ash melting point to 650-750 °C, which is why it fuses into slag in a hot cup.
Is it cost-effective to burn agro pellets instead of wood pellets?
Agro pellets cost 15-25% less and give only about 5% less heat (4.4-4.8 versus 4.7-5.0 kWh/kg), so per kilowatt-hour they come out about 15% cheaper. The savings are real when the boiler's passport allows husk and you can clean the cup every 2-3 days. If the boiler is borderline compatible, one shutdown in a frost costs more than the entire difference.
Can I mix agro pellets with wood pellets?
In a household burner it does not help: the ash content of a "half and half" mix is still 2-3%, and the potassium from the husk lowers the melting point of all the ash. Such a mix slags almost as much as pure husk. A flame burner needs wood pellets only.
Can I burn agro pellets in a solid fuel boiler with manual loading?
Yes, in a boiler with a grate agro pellets burn like small coal. They are added in a 5-10 cm layer on top of an already glowing bed of fuel, and the ash is shaken off the grate. There is no automation, but this method is economical.
How do I set up the burner so that agro pellets slag less?
Reduce the fuel feed per cycle by 10-20% and increase the air supply so the layer in the cup is thinner. Shorten the pause in standby mode, clean the cup on a schedule rather than when the burner has gone out, and do not keep the flow water temperature at maximum. These rules cut slagging roughly by half, but only in boilers that allow agro fuel. Before buying a batch, burn a trial bag in your own burner.
Buy the fuel covered in this article
Prices per tonne and per bag, stock and delivery across Ukraine are on the category page. For wholesale: special terms.
