Ask ten smiths which forge is best and you will get ten answers, usually delivered with a hammer in hand. The truth is that coke forges and gas forges do the same job by very different means, and the one that suits you depends on your work, your workshop, and how much patience you have for fire tending. Here is a practical comparison drawn from everyday use in a small shop.

The Two Approaches at a Glance

A coke forge is a firepot, a tuyere and a blast of air. You burn a solid fuel — usually smithy coke, sometimes coal you coke down yourself — and you control the heat by how much air you push through and where you place the metal in the fire. Everything is visible and immediate, and the fire is a living thing you learn to read.

A gas forge is an insulated chamber with a burner. A venturi burner draws its own air; a blown burner uses a fan for more control. You line the shell with ceramic fibre, rigidise it, coat it to protect against flux, and fire it with propane. Once tuned, it holds a temperature and stays there with almost no intervention.

Fuel Costs and What You Actually Spend

Solid fuel is usually cheaper per hour of forging, but the gap is narrower than people expect once you account for idle time.

• Coke — expect to pay roughly £15–£25 for a 25 kg sack from a coal merchant or farrier supplier. A working forge burns through 3–5 kg an hour when you are busy, more if you keep a big fire banked.
• Propane — a 19 kg refill runs around £40–£50, and a typical single-burner forge uses 1–2 kg an hour. A 47 kg cylinder is far better value per kilogram if you have somewhere safe to store it.
• Idle behaviour — a gas forge left running between heats costs you fuel every minute. A coke fire can be damped down, banked, and revived, so short breaks cost far less.

Buy coke in bulk where you can, keep it dry, and remember that a wet sack of fuel wastes heat drying itself out. For gas, a spare cylinder is not a luxury — running out mid-heat is a particular kind of frustration.

Temperature Control and Forge Atmosphere

This is where the two forges feel most different. A gas forge is repeatable. You set the regulator, watch the colour of the lining, and know that 1,100°C is 1,100°C every time. For heat treating, normalising, and any job where consistency matters, that counts for a great deal.

A coke forge is local and fierce. The heart of the fire will reach 1,300°C and beyond, hot enough for forge welding, while a hand's width away the metal is barely warm. You steer the work through the fire rather than waiting for a chamber to heat it. Scale behaves differently too: a clean coke fire with the right blast gives a reducing atmosphere that keeps oxides down, while a badly tuned gas forge produces generous flakes of scale. Tune the gas burner slightly rich and you get much of the same benefit.

The coke forge's price is clinker. Impurities melt and form a glassy lump that blocks the tuyere and kills your heat, so you slice it out with a poker and rake, sometimes several times in a session.

Lighting Up: Two Very Different Mornings

Starting a coke forge is a small ritual. Paper and kindling first, then wood, then a handful of coke or green coal around the edges, with the blast turned right down. You build the fire outward from the centre, adding fuel and air gradually. From cold to a working heat takes fifteen to thirty minutes, and rushing it produces smoke, steam and a sulking fire.

A gas forge is running in five minutes flat — valve open a crack, burner lit, then wind it up. The catch is that the lining needs to soak heat before it works well, so the first ten minutes feel sluggish. Both forges reward you for starting them before you need them.

Workshop Practicalities

• Ventilation — a coke forge needs a proper flue or hood and a clear chimney. A gas forge still needs ventilation: carbon monoxide is colourless and odourless, so a CO alarm is not optional.
• Storage — propane cylinders belong outside, upright, and away from heat. Coke wants a dry, covered bunker.
• Mess and noise — coke means ash, clinker, dust and the whine of a blower. Gas is quiet and clean, which matters if you share walls with neighbours.
• Portability — a small gas forge can be carried to a demonstration or a friend's shop. A coke forge travels as a firepot, a blower and a sack of fuel.

Which Forge Suits Your Work

If you make blades and need predictable soak times, or you work in a shed with limited space and awkward neighbours, gas is the easier introduction. If you forge weld regularly, work large sections, or simply enjoy the craft of the fire itself, coke gives you a heat that gas struggles to match at the same price.

Plenty of smiths end up with both: a coke forge for heavy welding and rough shaping, a gas forge for finishing and heat treatment. If you can, spend an afternoon at each before you commit your money. Your hands will tell you which one you want to light tomorrow morning.