Hardwood vs Softwood: Which Burns Better

Most firewood gets bought without anyone really checking what's in the bag. Some people might grab whatever's stacked at the garden centre, whatever the local supplier drops off, whatever's cheapest per cubic metre. Some of it is hardwood, a lot of it is softwood. And the difference matters more than most buyers realise.

The hardwood/softwood thing isn't marketing. It genuinely matters, and once you understand why, you stop buying mystery wood.

The names are a bit of a lie

"Hardwood" doesn't mean hard. Balsa is a hardwood and you can dent it with a fingernail. Yew is a softwood and it's harder than most oaks. The terms are botanical, not physical: hardwoods come from broadleaf trees that drop their leaves (oak, ash, beech, birch, hornbeam, alder), and softwoods come from conifers that don't (pine, spruce, fir, cedar, larch).

What you actually care about isn't the label. It's density.

Hardwoods typically grow slowly and pack more wood fibre into the same volume. A seasoned oak log feels heavy in your hand. A pine log of the same size feels like it's been hollowed out. That weight difference is fuel, and you're paying for the volume, not the mass, when you buy a bulk bag.

How much heat do you actually get?

Per kilogram, dry wood doesn't vary as much as you'd think. Most species sit between 4.5 and 5.4 kWh per kg at 20% moisture. Denser hardwoods like oak and ash are on the higher end of the scale, with less dense species: larch, pine and spruce around 4.5.  Therefore, weight for weight - oak only beats pine by about 10-20%.

The catch is that firewood is sold by volume in the UK, not weight. A bulk bag is a bulk bag, and that's where density does the heavy lifting.

When dried, solid oak weighs around 700 kg per cubic metre. Solid pine, around 440 kg. Solid spruce, around 400. So when you buy a bag of oak, you're getting roughly 50-70% more actual wood mass than the same-sized bag of pine, and that mass is what produces heat.

In real numbers, a typical bulk bag of kiln-dried oak (around 0.6-0.8m³ loose) gives you somewhere between 1,500 and 1,800 kWh of heat. The same-sized bag of pine or spruce gives you closer to 1,000-1,300 kWh. Denser softwoods like larch and Douglas fir close the gap a bit, but they don't close it entirely.

Why softwood can set your chimney on fire

This is the part nobody mentions when they're selling you the bag.

Softwoods are full of resin. When you burn them, the resin doesn't fully combust. It vapourises, drifts up the flue, and condenses on the cooler flue or chimney walls as creosote. Creosote is sticky, it's tarry, and it's flammable. When enough creosote builds, a stray ember from the fire can set the inside of your chimney alight. Chimney fires aren't theoretical. UK fire services attend over 31,000 chimney fires a year, and around 9,500 of those cause damage to the property. Most insurers won't pay out on a chimney fire claim unless you can prove the flue was professionally swept within the last year - and creosote buildup from burning the wrong wood is one of the main reasons those fires happen in the first place.

Hardwoods produce far less creosote because there's far less resin to begin with. You still need your flue swept, but you're not actively glazing it every time you light up.

What an evening actually looks like

A pine log gives you a bright, lively fire that's gone in 45 minutes to an hour. You'll be feeding the stove constantly to keep the room warm, and when you stop feeding it, it dies fast. There's nothing left in the firebox but ash.

Oak or ash burns slower and develops a thick bed of glowing coals as the flames die down. Those coals are the real prize. They keep radiating heat into the room long after the active flame is gone, and they let you go forty minutes between refuels instead of fifteen. A two-log evening becomes genuinely possible.

What this isn't, to be clear, is an excuse to load the stove and damp it down for the night. Slumber burns are a bad idea regardless of wood type. They choke the fire of oxygen, drop combustion temperatures, and produce the worst smoke, carbon monoxide and creosote of any burn pattern. Modern stove guidance is firmly against them. The point of good coaling hardwood is that you get a better evening, not that you can leave the fire unattended.

The real cost of burning softwood

People look at price-per-bag and assume softwood is the cheaper option. On the bag itself, it usually is. But that's not where the costs end up.

You burn through softwood faster. You handle more of it, store more of it, refuel more often. A winter's worth of softwood can be noticeably more bags than a winter's worth of hardwood for the same heat output, and every one of those bags has to be paid for, delivered, and stacked.

Then there's the chimney. Burning softwood as your main fuel means more creosote, which means sweeping the flue more often. A proper HETAS approved sweep runs £80-150. One extra sweep a year (or worse, a chimney fire), and any saving on the bag itself disappears.

The real cost-per-kWh comparison isn't on the price tag. It's the bag price plus the extra bags plus the extra sweeps plus the higher fire risk, divided by usable heat. By that measure, hardwood pulls ahead almost every time.

The "Ready to Burn" bit that matters

Since 2021, it's been illegal in England to sell wet firewood in volumes under 2 cubic metres. The rule comes from the Air Quality (Domestic Solid Fuels Standards) (England) Regulations 2020, and it means anything you buy in a net or a bulk bag has to carry the Ready to Burn logo and be under 20% moisture. This applies to both hardwood and softwood, and it's the single most important thing to look for on the bag.

Anything sold in larger volumes (2m³ or more) doesn't need the certification, but it must carry a drying notice. The assumption then being that bulk buyers will season the wood themselves before burning it.

Wet wood doesn't burn properly. It hisses, smokes, and dumps creosote into your chimney while giving you barely any heat. Buying Ready to Burn certified is the bare minimum, not a luxury.

This also kills off softwood's one historical advantage: it seasons faster. That used to matter when people cut their own. If you're buying from a supplier, the seasoning is their job, and you should be getting properly dry wood either way. Hardwood's slower drying time isn't your problem any more.

(Scotland, Wales and Northern Ireland have separate rules — but if you're buying certified Ready to Burn wood, you're meeting or exceeding the standard wherever you live.)

What softwood is actually good for

Kindling. Pine and spruce sticks light faster and easier than anything else. A handful of them under your hardwood logs is the right way to start a fire. That's softwood's actual job: getting the real wood going. When you buy kindling, it's almost always softwood. Beyond that, it doesn't earn its place as your main winter fuel.

So, what should you buy?

If you're heating a home, you want hardwood. Oak, ash, beech, birch, hornbeam, alder, any of the British natives, depending on what's local and what's available. Ready to Burn certified, under 20% moisture, in a bulk bag rather than tiny shrink-wrapped nets.

Keep some softwood around for kindling. Beyond that, anything cheap and unlabelled is almost always pine, almost always wetter than it should be, and almost always a worse deal once you do the actual sums.

Buy the heavy stuff. Your stove, your chimney, and your evening will all be better for it.