Start With What You Can Actually Get

A forge is only ever as good as the fuel you can reliably shovel into it. Before comparing flame temperatures or price per bag, answer two practical questions: what can you buy within reasonable driving distance, and what are you actually allowed to burn where you live? Across much of England, Scotland and Wales, built-up areas are designated smoke control areas, where only authorised smokeless fuels may be burned. A coal fire in a suburban back garden will attract complaints long before it attracts admiration, and your local council's environmental health team can act on them.

Ask around your local blacksmithing group, the agricultural merchant, or the farrier's supplier. They usually know who keeps coke in stock and who will drop a tonne of coal on your drive at a sensible price. Bulk buying transforms the economics, but only if you have somewhere dry and secure to store it.

Coal: The Traditional Standby

Bituminous smithing coal, sometimes sold simply as smithy coal, is what most people picture when they think of a blacksmith's fire. Its great virtue is that it cokes as it burns. The volatiles drive off, the coal swells and fuses into a soft, sticky mass, and you are left with a bright, intense coke core surrounded by a bank of green coal. That bank is your insulation, and it is why a coal fire can be hollowed out into a deep, localised welding fire with a bit of practice.

The drawbacks are real: smoke on start-up, a smell that clings to clothing, and clinker — the fused, glassy residue that creeps across your air supply and has to be broken out and removed. It is dirty to handle, too. A small forge will get through perhaps two to four kilogrammes of coal in a couple of hours of solid work. Bagged coal from a blacksmithing supplier tends to run around £20–£30 for 25kg, while bulk delivery is far cheaper per kilogramme if you can take a tonne and keep it dry.

Coke: Coal Without the Smoke

Coke is coal that has already had its volatiles driven off before it reaches you. It lights harder and demands a deeper fire and a decent blast of air, but once it is going it burns with very little smoke, produces far less clinker, and holds its shape rather than swelling. For anyone in a smoke control area, or simply with close neighbours and a low tolerance for complaints, that is often the deciding factor.

A coke fire is thirsty for air and unforgiving of a shallow firepot — it wants depth, and it wants a good draught beneath it. Many smiths run coke for everyday work and switch to coal when they need that sticky, controllable fire for forge welding. Coke comes through solid fuel merchants, usually in 25kg bags or by the tonne, and it stores well provided it stays dry.

Charcoal: Clean, Quick, and Hungry

Lumpwood charcoal is the oldest forge fuel of all, and easily the pleasantest to use. It lights without fuss, produces almost no smoke or clinker, and gives a clean, bright fire free of sulphur. You can work in a small space with the door open, and the fire answers quickly when you change the blast.

The catch is appetite. Charcoal burns down fast, so you will be topping up constantly, which makes it fiddly for long or repetitive work. It sparks, so keep the area around the forge clear of anything flammable. Expect to burn three to five kilogrammes in a session, and be choosy: proper lumpwood far outperforms briquettes, which crumble and may be bound with additives that foul your fire. Budget roughly £1.50–£2.50 per kilogramme in small quantities.

Propane: Consistency in a Bottle

A gas forge sidesteps fuel handling altogether. Turn a valve, light it, and you have stable, adjustable heat with no ash, no clinker and no smoke. Propane burns cleanly and predictably, which makes it excellent for blade work and for anyone forging in a small shed or workshop with sensible ventilation.

It is not a like-for-like swap. You need a purpose-built gas forge with a refractory lining and burner, plus a regulator and hose, and you will be running it from a 13kg or 47kg cylinder. A single-burner forge typically consumes around half a kilogramme to a kilogramme of propane an hour, so a 13kg cylinder gives perhaps fifteen to twenty hours of forging. Refills are inexpensive, but the initial outlay and cylinder deposit are not. Gas forges also tend to run an oxidising atmosphere, which means more scale on your work, and they are less suited to the deep, tightly localised heat that some traditional joints demand.

Weighing Up Cost, Smoke and Convenience

There is no single right answer, only the answer that fits your workshop, your neighbours and the work you do. As a rough guide:

• Smoke-sensitive site or built-up area: coke, charcoal or propane will keep you out of trouble. Coal almost certainly will not.
• Tight budget with space to store in bulk: coal remains the cheapest heat per hour by a wide margin.
• Small, clean, occasional forging: charcoal is forgiving to learn on and needs minimal kit.
• Consistency and low fuss: propane wins, especially for blades and repetitive work.
• Best of both worlds: keep a solid fuel firepot and a gas forge, and match the fuel to the job.

If you are new to this, buy a small quantity of two or three fuels rather than committing to a tonne. Your forge, your neighbours and your hands will tell you fairly quickly which one suits. The fire always has the final word.