How to Turn Wood Chips and Yard Waste Into Pellets
You can turn wood chips and pruning waste into pellets in five steps: sort the material, crush it, dry it, grind it fine and press it. Chips cannot go straight into a pellet mill, because they are too coarse and usually too wet. Fresh chips can be around 50% moisture, and they need to reach roughly 10 to 15% before pressing. Clean, bark-free wood makes the best pellets. Leaves, soil and bark all raise ash, which decides what you can do with the finished product.
Step 1: Sort what comes in
Your feedstock decides your market, so sorting is the most important step.
Material | Use it? | Why |
|---|---|---|
Clean branches and orchard pruning | Yes | Good base material. Bark raises ash somewhat |
Sawmill slabs and clean offcuts | Yes | Often the best and driest option |
Mixed arborist chips | With care | They mix wood, bark and often leaves, so ash varies by load |
Leaves and needles | Keep separate | Higher ash and chlorine. See our leaf pellet guide |
Stumps, roots, soil-covered wood | No | Soil contamination can push ash to 6 to 10% and wears the die |
Painted or treated wood, plywood, pallets | No | Toxic when burned, and prohibited in residential wood heaters |
Lawn clippings | No | Too wet, and better composted |
Diseased or quarantined trees | Check first | Moving wood can spread pests and may be restricted |
If you accept waste from other people, your state may treat you as a waste or composting facility. Rules vary, so ask your state environmental agency before you take in outside loads.
Step 2: Crush branches into small pieces
A wood crusher handles branches, slabs, bamboo and straw. Our MK-FSD series cuts wood into chips, passes them through a hammer chamber until they become sawdust, then sends them up a cyclone into a bag. That can combine this step with grinding.
If you already have a chipper, use it here and move on to drying.
Keep stones and metal out. Tree service loads can carry nails, wire and gravel, and any of them can damage hammers and dies.
Step 3: Dry it
This is usually the most expensive step. Industrial plants take chips from about 50% moisture down to about 12% before milling.
For small volumes, air drying works. Pile the chips under a roof with good airflow, turn them regularly, and be patient. For larger volumes you will need a rotary or belt dryer. Check with a moisture meter, and aim for 10 to 15% before pressing. Our MKRD250C-W ring die mill, for example, specifies raw material moisture of up to 13%.
Fire warning. Large piles of damp chips can heat themselves and catch fire. Keep piles modest in size, monitor their temperature, and keep them away from buildings.
Step 4: Grind it fine
A hammer mill turns dry chips into fine, uniform material. Particles should be smaller than the die holes. A 1/4 inch (6 mm) screen is a common starting point for a 6 mm die, with a finer screen if pellets come out rough. Some materials need a second pass.
Grinding dry material makes dust, and wood dust is combustible. Use a cyclone or dust collector, ground your equipment, clean up regularly, and never let dust build up on beams or motors.
Step 5: Press, cool and store
Feed the mill steadily, starting with a 6 mm die.
Clean wood: a standard flat die pellet mill works well.
Bark-heavy or mixed material: a rotating roller model presses harder and handles material that binds poorly.
Continuous production: a ring die pellet mill.
Let pellets cool before bagging, so they harden and do not sweat. Screen out fines and run them again. Store pellets dry and in a ventilated area. Bulk wood pellets can give off carbon monoxide and use up oxygen in closed storage, so never enter a closed bin or silo without ventilating it and checking the air.
Where can these pellets go?
Use | Fit | What to know |
|---|---|---|
EPA-certified residential heaters | Only if graded | Federal rules limit these heaters to pellets graded under a third-party program such as PFI, ENplus or CANplus, and prohibit yard waste |
Commercial and industrial boilers | Good | Match the boiler's ash and moisture limits and your air permit |
Animal bedding | Good | Clean, soft wood works well, and horse bedding is an established market. Avoid black walnut, which is toxic to horses |
Soil amendment or mulch | Good | A way to use material with more bark and leaves. State rules apply if you sell it |
Mushroom substrate | Niche | Growers use clean hardwood pellets, so bark-free hardwood is the requirement |
Quality comes down to bark, foliage and soil. An Irish forestry note lists pure wood pellets at about 0.5 to 0.7% ash, and each of those three pushes that number up quickly. Send a sample to a lab before you promise a grade to anyone.
Does it pay?
Free feedstock is not free. You still pay for loading, crushing, drying and grinding. The numbers usually work best in these situations:
Tree services and landscapers who pay to dump chips today
Orchards and vineyards with annual pruning that would otherwise be burned or left in piles
Sawmills and woodworking shops with dry, clean residue, which is the easiest case of all
Municipalities with green waste programs
Write down your tons per year, moisture, distance to buyers and current disposal cost. Those four numbers tell you most of what you need to know.
Frequently asked questions
Can I press wood chips directly? No. Chips must be ground to fine particles first, and almost always dried.
Can I make pellets from chips delivered by a tree service? Yes, but expect a mix of wood, bark and leaves that changes from load to load. Screen out large pieces, and test ash before selling as fuel.
How long does it take to air dry chips? It depends on climate, pile depth and turning. Use a moisture meter instead of a calendar.
Will my pellets meet premium grade? Clean, debarked wood can get close, but only a licensed third-party program can grade them. PFI premium allows no more than 1% ash.
What is the smallest setup? A small hammer mill like the MKH158B and a small flat die mill can process trimmings from your own property, once they are chipped and dried.
Can I use the pellets in my own stove? Check the owner's manual first. Certified heaters are limited to graded pellets. See our note in How to Make Wood Pellets at Home.
Tell us about your material
Send us your material, tons per year and moisture, and we will help you plan a line. See what to prepare for a quote.
