Choosing the right fuel for your stove or fireplace changes everything. Good logs produce steady warmth, clean glass, and minimal soot. Poor logs create thick smoke, tar in the flue, and very little real heat. Many homeowners buy logs without knowing how density, species, and water content affect their stove.
This guide serves as your comprehensive resource for making sensible buying decisions. It forms a central component of our master resource, Firewood 101: A Homeowner’s Guide to Efficient Wood Burning and Heat Management. When you know what to look for, you get better value for money and a far warmer home.
To get the most out of your heating system, you also need to know How to Store and Season Firewood Correctly once your delivery arrives. You will also want to understand How to Burn Wood Efficiently and Manage Stove Heat to ensure every log delivers its full heating potential.
Understanding Wood Density: Hardwood vs Softwood
All firewood is categorised into two broad botanical groups: hardwoods and softwoods. The main difference lies in how fast the tree grew and how dense the wood fibres are.
Hardwoods come from slow-growing broadleaf, deciduous trees like oak, ash, beech, and birch. Because these trees grow slowly, their wood cells pack closely together. A cubic metre of hardwood is noticeably heavier than a cubic metre of softwood. This density translates directly into energy density. A single hardwood log burns for a long time and leaves behind a bed of glowing embers. It suits everyday winter heating in an enclosed stove.
Softwoods originate from evergreen, cone-bearing conifers like pine, spruce, larch, and fir. These trees grow rapidly. Their timber has open, porous cellular structures. Softwoods catch fire quickly and burn with tall, lively flames. They release their energy fast and produce a sharp burst of heat. Softwood is ideal for kindling and for warming up a cold chimney flue quickly. For an in-depth breakdown of which wood suits specific appliances, read our detailed comparison on Hardwood or Softwood: Which Is Better for Your Log Burner?.
| Wood Species | Type | Heat Output | Burn Speed | Primary Homeowner Benefit |
|---|---|---|---|---|
| Ash | Hardwood | Very High | Moderate | Low sap levels; creates a steady, calm flame |
| Oak | Hardwood | Exceptional | Slow | Longest burn time; creates long-lasting embers |
| Silver Birch | Hardwood | High | Fast to Moderate | Catches easily; attractive bark and bright flame |
| Beech | Hardwood | Very High | Slow | Smooth bark; dense structure with high heat |
| Scots Pine | Softwood | Medium | Fast | Pleasant resinous scent; brilliant for starting fires |
Moisture Content: The Most Critical Factor
Species matters, but moisture content matters much more. A wet piece of oak will burn terribly, while a dry piece of soft pine will burn cleanly and efficiently. Newly felled timber contains between 45% and 60% water by weight. If you burn green timber, the fire must first boil that water away before it can release sensible heat into your room.
Water turns to steam, lowering the firebox temperature. This cooling effect prevents complete combustion. Instead of clean warmth, your chimney fills with unburned gases, volatile organic compounds, and steam. This sticky mixture cools inside the flue pipe to form creosote. Creosote is a corrosive, highly flammable tar that ruins metal flue liners and causes chimney fires.
To protect your home and stove, firewood must have an internal moisture reading below 20%. Logs can reach this level through natural air-drying over several seasons, or through industrial drying kilns. To determine which drying method suits your budget and storage capacity, check out our guide on What Is Kiln Dried Firewood and Is It Worth It?.
UK Clean Air Regulations: The Ready to Burn Standard
Domestic heating rules across the United Kingdom changed significantly under the Clean Air Strategy. It is now illegal for retailers in England to sell wet firewood in small volumes of under two cubic metres. All firewood sold in units under two cubic metres must be independently certified to guarantee moisture content below 20%.
This initiative is managed through Woodsure. Certified bags carry the clear Ready to Burn logo alongside the supplier's unique registration number. This standard protects consumers from buying damp timber that damages appliances and pollutes local air. Before purchasing fuel, familiarise yourself with the full rules outlined in A Guide to the UK Ready to Burn Certification Scheme.
If you live inside a designated Smoke Control Area, compliance is especially crucial. Stoves installed in these zones must be Defra-exempt appliances operated with approved dry fuels. Burning wet, uncertified logs can result in council fines of up to £300, alongside persistent issues with your neighbours due to excessive chimney smoke.
Selecting the Correct Log Dimensions
Many homeowners overlook the physical size of the logs they order. A load of firewood might be dry and dense, but if the pieces do not fit your stove, you will face frustration and extra labour with an axe.
- Standard Length: Most modern UK log burners feature fireboxes designed to accept logs 25 centimetres (10 inches) long. Always measure your firebox width before placing an order.
- Split Diameter: A healthy fire needs logs of varying thicknesses. Small splits measuring 6 to 8 centimetres across are ideal for building heat quickly. Thicker logs measuring 10 to 15 centimetres across are best added once the stove reaches its optimal operating temperature.
- Square Cuts: Look for logs with clean, flat-sawn ends. Flat-sawn logs stack neatly inside your log store and remain stable inside the firebox, reducing the risk of heavy wood rolling against the front glass pane.
Buying Quantities: Volume vs Weight
Never purchase firewood by weight alone. Weight is a misleading metric because water is heavy. An unscrupulous seller offering a tonne of wood might simply be selling you half a tonne of dry timber and half a tonne of useless trapped water.
Reputable merchants sell wood by volume, usually in loose cubic metres, stacked cubic metres, or cubic-metre builders' bulk bags (dumpy bags). Be aware that a loose cubic metre holds approximately 30% to 40% less solid timber than a neatly stacked cubic metre of the same dimensions. Factor these differences into your price comparisons.
Mortimers Fuel Tip: If you have dry outdoor space, buying hardwood bulk bags during the spring and summer offers significant cost savings compared to purchasing small convenience bags from petrol stations during mid-winter cold snaps.
Common Wood Buying Mistakes to Avoid
Avoid these common traps when purchasing winter firewood:
- Burning Construction Offcuts: Treated timber, fence posts, painted floorboards, and plywood contain toxic adhesives, copper, and arsenic. These chemicals release poisonous fumes and corrode your stove liner.
- Assuming All "Seasoned" Wood Is Dry: The term "seasoned" has no strict legal definition unless backed by the Ready to Burn certification. Wood left under an unventilated tarpaulin for two years may still be damp and mouldy.
- Relying Exclusively on Fast-Burning Softwoods: While softwood heats up quickly, relying on it entirely means restocking your firebox every 40 minutes, leading to high fuel consumption over an evening.
Frequently Asked Questions About Choosing Firewood
Can I burn freshly cut wood from my garden?
No. Freshly cut wood contains high levels of sap and moisture. It will hiss, smoulder, blacken your glass, and deposit dangerous creosote inside your chimney. You must split and season garden wood for 12 to 24 months until its moisture drops below 20%.
Which firewood produces the most heat?
Dense hardwoods like oak, beech, and hornbeam provide the highest heat output per log. They burn slowly and maintain a bed of glowing charcoal that radiates heat long after the flames die down.
Is birch good firewood?
Silver birch is an exceptional fuel. Its bark lights easily and the wood burns with a bright, lively flame and very pleasant scent. However, because birch is slightly less dense than oak, it burns through a bit faster.