Best Wood to Burn: Why Species Matters Less Than You Think

Ask ten people what the best wood to burn is and you will get ash, oak, beech and a story about someone’s grandfather. The species argument is the loudest one in wood heat, and it is mostly the wrong argument, because the thing everyone is arguing about is not what decides how much heat comes out of your stove.

Here is the physics, sourced to Forest Research rather than folklore, then the five species compared on the measure that does matter, then what to do with the answer when you are buying.

The uncomfortable fact: dry wood is dry wood

Forest Research’s Wood as Fuel technical supplement, published by the Biomass Energy Centre, puts it in one sentence: “There is little variation of CV between species when tested at the same moisture content.”

CV is calorific value, the heat available per unit of fuel. The same document explains why the species myth persists. Most of the apparent difference between species is really a difference in how wet they are when felled. As it puts it, “fresh poplar timber will have about half the CV of fresh ash, but if both are dried to the same moisture content they will have a very similar CV per weight”.

So a kilogram of properly seasoned birch and a kilogram of properly seasoned oak will give you close to the same number of kilowatt hours. That is not a marketing claim from someone selling softwood. It is Crown Copyright.

What the same document is equally clear about is which variable does matter: “The moisture content of wood has the greatest effect on CV of any of the variables.” Wet wood is worse than any species choice you could make, because the water has to be boiled off before the wood will burn, and the energy to do that comes out of your fire.

Everything else on this page is a second-order effect sitting on top of that one.

What species actually changes: density

Species does not change the heat per kilogram much. It changes the heat per log, and the heat per cubic metre, because dense timber packs more wood into the same space.

Forest Research again: “As hardwood species are generally denser than softwood species, a tonne of hardwood logs will occupy a smaller space than a tonne of softwood logs. Dense woods will burn for longer than less dense woods, this means you will need fewer ‘top ups’ to keep a log stove burning. If you measure wood by volume you will generally receive more kilowatt hours (kWh) of heat from a cubic metre of hardwood than softwood.”

That is the whole species question, honestly stated. If you buy by weight, species barely matters. If you buy by volume, which almost everyone in the UK does because logs are sold by the cubic metre, the bulk bag or the crate, then density is worth real money, and a dense species means fewer trips to the log store on a January evening.

The five species, compared honestly

Roughly ordered by density, densest first. Treat these as tendencies rather than laboratory constants, because density varies with growth rate and where the tree grew.

Hornbeam

The densest common British firewood, and if you are buying by volume it gives you the most heat per cubic metre of anything on this list. It burns slowly and steadily and holds a fire overnight better than anything except perhaps well-chosen oak.

It is also hard work. Hornbeam is genuinely difficult to split by hand, the grain is interlocked and it dulls tools. If you are splitting your own, factor that in. It is uncommon in commercial log sales, so you will mostly meet it if you have a local supply.

Oak

The species with the best reputation and the longest wait. Oak is dense, burns long and slow, and produces excellent, long-lived embers, which is why it is the traditional overnight wood.

The catch is seasoning time. Oak is slow to dry, and the usual guidance of two years air-drying is not folklore, it reflects genuinely low permeability. Oak sold as seasoned after one summer is frequently not, and burning it wet wastes exactly the density advantage you paid for. If you are buying oak, a moisture meter is not optional. It is also higher in tannic acid than most, which is one reason it is not the wood to burn in a stove you have let run cool and smoky.

Beech

Excellent firewood and, in practice, the one many people find they like best. Dense, splits cleanly, burns hot with a bright flame and good embers.

Beech has one specific weakness worth knowing: it is unusually good at reabsorbing moisture from the air. Beech that was dry in September can measure wet in December if it has been stacked somewhere damp or left uncovered. Whatever you do about storage, do it properly for beech. Our log store size calculator will tell you what you need to build.

Ash

The one with the best working reputation in Britain, and there is a real reason behind the folklore: ash has a lower moisture content standing than most species, so it comes closer to burnable sooner. That is precisely the effect Forest Research identifies as the source of most between-species differences.

It does not mean you should burn it green. “Burns well even when green” was true relative to oak in an era of open fires; it is not true relative to the 20 per cent moisture standard a modern stove and the law both expect. Season it like anything else.

There is a live reason ash is unusually available at the moment. Ash dieback has moved through most of the country and is producing a large volume of felled ash. Forest Research’s chalara management guidance states that spread of the disease in wood is considered low risk, so “ash wood from infected as well as uninfected sites may continue to be moved without restriction within Great Britain”, with the sensible precaution of brushing leaf and shoot material off logs before they leave a site. Burning it is fine.

The practical warning is different: dead standing ash degrades. Wood that has been dead in the tree for a few years goes punky and light, and light wood is low-density wood, which is the one thing that actually matters. Cheap ash is often this. Pick a log up. If it feels like it weighs nothing, it will heat like it weighs nothing.

Birch

The fast one. Birch lights easily, burns hot and bright, and is genuinely lovely to watch, which is not nothing if you have a glass door. Its bark is one of the best natural firelighters there is.

It is also the least dense of the five, so it burns through quickly and you will be refuelling more often. Birch bark contains oils that burn very readily, which is a feature at the start of a fire and a reason not to load a cold stove with nothing but birch and expect a controlled burn. The standard approach is right: birch to get going, something denser to keep going.

What about softwood?

Burning softwood does not cause chimney fires. Burning wet wood causes chimney fires, and softwood has historically been sold wetter and burned in cooler fires, which is where the reputation came from.

Forest Research’s position is the practical one: you get fewer kilowatt hours per cubic metre from softwood, but “softwoods are often cheaper and easier to source”. Dry spruce or larch in a stove running properly is perfectly good fuel. It spits more, so it is poor on an open fire, and it burns down faster, so it needs more attention.

If your supplier’s softwood is genuinely dry and genuinely cheaper per kWh, it is a rational buy. Work it out rather than assuming, using our firewood price comparison calculator.

What you must not burn

Not a matter of preference.

Treated, painted or preserved timber, including old fence posts and decking, releases genuinely toxic products of combustion and can leave arsenic and copper compounds in the ash. MDF, chipboard and plywood contain adhesives that do the same. Driftwood carries salt, which turns into hydrochloric acid in the flue and corrodes the liner. Anything that arrived with a plastic coating, laminate flooring included, stays out of the stove.

And in England, wet logs are not just a bad idea, they are regulated. Wood sold in units under 2m³ must be certified below 20 per cent moisture. Our page on Ready to Burn sets out what the rules actually say and what the logo does and does not guarantee.

So what should you buy?

In order.

Buy dry, then worry about species. Under 20 per cent, measured, not claimed. Everything on this page is a rounding error next to that. What moisture should firewood be covers the number and how to use a moisture meter covers checking it, on a freshly split face, at room temperature, not on the outside of a cold log.

Buy dense if you are buying by volume. Beech, oak, hornbeam and a decent ash all give you more heat per cubic metre than birch or softwood. If you are paying by the cubic metre, that difference is the whole of your species decision.

Mix deliberately. Birch or softwood to establish the fire quickly and get the flue warm, then dense hardwood once it is up to temperature. This is better than either alone.

Watch the volume unit, not just the species. Forest Research notes that “1m³ loose volume is approximately 0.66m³ stacked volume”. A cubic metre of loose-tipped logs is around two thirds of a cubic metre of stacked wood, and suppliers do not always make clear which they mean. Our firewood volume converter handles the arithmetic, and boxed logs vs a bulk pallet covers where the real cost sits.

If you would rather not manage seasoning at all, kiln-dried logs and briquettes solve the moisture problem by removing it from your control, at a price. We cover both in the best kiln-dried logs in the UK and kiln-dried logs vs briquettes.

Frequently asked questions

What is the best wood to burn in a wood burner? By heat per cubic metre, hornbeam, then oak and beech, then ash, then birch, then softwood. But Forest Research is clear that there is little variation in calorific value between species at the same moisture content, so a well-seasoned birch log beats a poorly seasoned oak log every time. Buy on dryness first and density second.

Is ash really the best firewood? Ash has the best reputation in Britain because it holds less water standing than most species, so it reaches a burnable state sooner. That is a seasoning advantage, not a heat advantage. Dried to the same moisture content, ash is close to beech and slightly below oak on density. It is excellent wood, and it is currently plentiful because of ash dieback.

Can you burn ash affected by ash dieback? Yes. Forest Research states that spread of the disease in wood is considered low risk and that ash wood from infected and uninfected sites may be moved without restriction within Great Britain, with the precaution of brushing leaf and shoot material off logs before they leave the site. The practical caution is that long-dead standing ash goes light and punky, and light wood gives less heat.

How long does oak need to season? Around two years air-drying in the UK, and that figure reflects how slowly oak gives up water rather than tradition. One summer is not enough. Check with a moisture meter on a freshly split face rather than trusting a supplier’s description, and see our firewood seasoning time calculator for other species.

Does burning softwood cause chimney fires? No. Burning wet wood and running a stove too cool causes creosote to build up in the flue, and that is what causes chimney fires. Softwood acquired the reputation because it was often sold wetter and burned in cooler fires. Dry softwood in a properly run stove is acceptable fuel; it simply gives fewer kilowatt hours per cubic metre and burns down faster.

Which wood burns the longest overnight? Dense hardwood, so hornbeam, oak or beech, in large split pieces rather than small ones. Log size matters as much as species here, because surface area drives the burn rate. No wood will hold a stove overnight if the wood is wet or the air controls are set too open.

Is birch a good firewood? Yes, for a specific job. Birch lights easily, burns hot and bright, and its bark is one of the best natural firelighters available. It is the least dense of the common hardwoods, so it burns through fast. Use it to start a fire and to warm the flue, then move to something denser.

Does the species affect how much soot and tar I get? Far less than moisture content and how you run the stove. Wet wood and a starved air supply produce a cool, smoky burn and deposit creosote, whatever species you are burning. Resinous softwood burned cool is worse than hardwood burned cool, but the fix in both cases is dry fuel and enough air to keep the flue hot.