Hay Pellets for Heating: Heat Value, Ash and Which Burners Accept Them

Hay pellets for heating are compressed dried hay with a heat value of roughly 4.5 kWh per kilogram, slightly below good wood pellets, and they leave more ash. They only suit burners whose manufacturer approves agricultural fuel, so check the manual before you buy a single bag.

This guide explains what hay pellets are, how they compare with wood pellets, what ash and slagging mean in practice, which burners accept them and how to store them.

What are hay pellets?

Hay pellets are made by drying and grinding hay or meadow grass and pressing it through a die. The natural lignin and heat of pressing hold the pellet together, so no binder is needed. The result is a small cylinder, usually 6 to 8 mm in diameter, that can be poured, stored in bags or big bags and fed by an auger.

They belong to the group of non-woody or agricultural pellets, which also includes straw, miscanthus and reed canary grass. The international standard for this group is ISO 17225-6, which is separate from the wood pellet standard ISO 17225-2 that ENplus is built on. This difference matters, because the two groups of fuel behave differently in a burner.

Our shop lists DIN hay pellets for heating. The product page states a heat value of 16 to 19 MJ/kg, which is the supplier’s declared range. Always compare a declared range with the datasheet of the batch you receive.

How does the heat value compare with wood pellets?

One laboratory study of pellets made from straw, hay and blends measured 16.07 MJ/kg for hay pellets and 17.00 MJ/kg for straw pellets. Converted, that is about 4.5 kWh/kg for hay and 4.7 kWh/kg for straw. Wood pellets of ENplus A1 quality have a net calorific value of at least 16.5 MJ/kg, which is about 4.6 kWh/kg, and many batches reach 4.8 to 5.0 kWh/kg.

In practice, hay pellets deliver about the same heat per kilogram as an average wood pellet and a little less than a good one. Because bulk density also matters, check it too. The same study found a bulk density of about 480 kg/m³ for hay pellets, below the 600 kg/m³ that ISO 17225-6 asks for. Lower bulk density means a bag or silo holds less energy for its volume.

Property	Hay pellets	Wood pellets (ENplus A1)
Net calorific value	About 16 MJ/kg in the cited study (about 4.5 kWh/kg); supplier ranges up to 19 MJ/kg.	At least 16.5 MJ/kg (about 4.6 kWh/kg)
Ash content	Higher than wood, varies by batch and cutting date	Up to 0.7% for A1
Bulk density	About 480 kg/m³ in the cited study	Higher; check the datasheet.
Standard	ISO 17225-6 (non-woody)	ISO 17225-2 and ENplus
Typical burner	An agricultural or multi-fuel boiler is approved for it.	Pellet stoves and boilers

How much ash do hay pellets leave?

Hay contains more mineral matter than wood because grasses take up silica, potassium and other minerals from the soil. A review of pellets from different sources found ash contents of 9.1% and 10.5% in wheat and barley straw pellets, against 0.9% to 4.8% for the woody pellets in the same review. Hay is a different material from straw, but the same pattern applies: herbaceous fuels leave more ash than wood.

The ash limit for the non-woody pellet grade in a New Zealand wood fuel technical guide is 10 % by weight, compared with 0.7 % for ENplus A1 wood pellets. Our product page lists a much lower ash value for DIN hay pellets, from 0.2 to 0.5%. Treat any ash figure as a declared value for a given batch. Ask for a laboratory report if the ash value matters for your boiler.

More ash means a fuller ash pan, more frequent emptying and, in a stove, more frequent burn pot cleaning. Plan for that before you switch fuels.

What is slagging, and does it affect hay pellets?

Slagging is the formation of hard, glassy lumps from ash that melts on the hot parts of a burner. It blocks air holes in the burn pot, interrupts the fire and can damage a grate. The risk rises when the ash melts at a low temperature.

The New Zealand guide notes that non-woody fuels can cause fouling and slagging, especially when the feedstock has high potassium and silicate contents and little calcium. Hay and grass often fit that description, but results differ between batches, so the risk cannot be stated as a fixed number. A burner with a moving grate or automatic ash removal copes better than a simple fixed pot.

You can lower the risk in three ways. Buy pellets with a declared ash and ash melting value from the producer. Run the burner at the settings the manual recommends for that fuel. Inspect the burn pot for clinkers every few days during the first weeks, and adjust your cleaning schedule from what you find.

Do hay pellets cause corrosion?

They can, in some boilers, but the evidence depends on the fuel and the boiler. The same guide states that non-woody pellets have higher chlorine, nitrogen and sulphur contents than wood pellets and advises attention to corrosion risk in small and medium boilers. Chlorine can form hydrochloric acid in the flue gas, and condensation raises the risk further.

This is a reason to avoid running hay pellets in an appliance that was only designed for wood. Boilers built for agricultural fuel often use corrosion-resistant materials and keep flue gas temperatures above the dew point. If a manufacturer does not name hay or grass pellets in the approved fuel list, treat the burner as unsuitable.

Which burners accept hay pellets?

There is no general rule that covers all models, so the manual and the manufacturer decide. As a guide, three groups exist:

• Standard wood pellet stoves: usually approved for wood pellets only, often ENplus A1. Using hay pellets can void the warranty and cause slagging.
• Wood pellet boilers: most are approved for wood pellets as well. A few models are tested for a wider fuel range, and the boiler data sheet will say so.
• Agricultural, multi-fuel and industrial boilers: built for herbaceous fuels, with a stronger grate, ash removal and a flue gas path suited to higher chlorine.

Ask your installer or the manufacturer for written confirmation that hay pellets are an approved fuel for your model and size of pellet. Also check local emission rules, because chimney sweeps and inspectors in some countries test emissions against the fuel class.

How should you store hay pellets?

Hay pellets take up moisture more readily than many wood pellets and can crumble when wet. Keep them in a dry, closed room off the ground, in sealed bags or in a silo with a dry vent. Avoid outdoor storage under a tarpaulin, because condensation forms under the sheet.

Check pellets for fine dust before you fill the hopper, and sieve the dust out if the burner manual asks for it. Our guides on pellet storage and humidity and on moisture content cover the principles. They are written for wood pellets, but the same rules on dryness and handling apply to hay pellets.

Use older bags first, and do not keep more than one heating season of fuel. Stored hay pellets that smell musty or feel soft are better discarded than burnt.

How to decide whether hay pellets are right for you

1. Read your burner manual and find the list of approved fuels.
2. Ask the manufacturer in writing if hay pellets are not listed.
3. Request the producer’s declared ash, moisture and heat value for the batch.
4. Compare the price per kWh, not per tonne. Use about 4.5 kWh/kg for hay pellets as an estimate.
5. Start with one bag or a small test quantity before you order a full season.

If your burner is a standard stove, wood pellets are the safer choice. Our buyer’s guide to ENplus A1 pellets explains how to choose them, and the ENplus certification guide explains what the label covers. ENplus describes itself as a certification scheme for wood pellets, so it does not apply to hay pellets.

Key takeaways

• Hay pellets give about 4.5 kWh/kg, close to but a little below good wood pellets.
• Ash content is higher than for wood pellets and varies by batch, so ask for a lab report.
• Slagging and corrosion are possible, mainly in burners not built for agricultural fuel.
• Only burn hay pellets in a burner whose manufacturer approves them.
• Store them dry and sealed, and test a small quantity first.

If your boiler is approved for them, see our DIN hay pellets for heating. For stoves and standard boilers, see our EN Plus A1 wood pellets.

FAQ

Can I burn hay pellets in a wood pellet stove?

Only if the manufacturer lists them as an approved fuel. Most wood pellet stoves are approved for wood pellets alone, and hay pellets can cause slagging or void the warranty.

Are hay pellets cheaper than wood pellets?

It depends on the market and the season, so compare the price per kWh rather than per tonne. Extra ash handling and maintenance can offset a lower purchase price.

Do hay pellets smell when they burn?

They can smell differently from wood pellets because hay has a different composition. A strong or acrid smell may point to damp fuel or poor combustion, and the burner settings should be checked.

How long can I store hay pellets?

Dry, sealed pellets can be kept through a heating season. Damp conditions break pellets down quickly, so storage conditions matter more than time.

Is the ash from hay pellets usable in the garden?

Rules differ between countries, and the ash may contain concentrated minerals. Check local waste regulations before you spread it, and do not assume it is suitable for every soil.