Old Coal-Burning Fireplaces: Can You Burn Wood?

How to recognize a coal fireplace

Many city houses built before central heating were warmed room by room, and in much of the Northeast that meant coal. Brownstones, Philadelphia rowhouses and older Jersey City and Hoboken row homes often have a coal fireplace in every main room, each with its own small flue. They have a look of their own, and you can usually spot one without moving anything.

• A small, shallow opening, often with an arched top
• A cast iron surround, sometimes with a decorative summer cover that fits over the opening
• An iron coal grate or basket standing on legs or built into the front
• A firebox lined with iron plates or thin brick rather than full-size firebrick
• A narrow flue, frequently with no damper at all

Why coal and wood need different fireplaces

Coal burns in a compact, glowing bed. Air comes up through the bars of the grate from below, the fire stays low and steady, and it gives off a lot of radiant heat from a small volume. A coal fireplace only needed a modest opening, a shallow firebox to throw that heat into the room, and a small flue to carry the relatively modest volume of combustion gas.

Wood is the opposite. A log fire is taller and looser, it burns in flames rather than a glowing bed, and it releases much more smoke and water vapor, especially in the first half hour. It needs room above and behind it, plenty of air, and a flue big enough to move that smoke away quickly. Put logs into a shallow coal firebox and the fire sits right at the opening. Smoke rolls out the front, sparks reach the hearth, and heat hits the mantel and wood trim far harder than they were built to take.

The flue behind a coal fireplace

Usually the bigger limit is the flue. Coal flues in old row houses tend to be small, and many were built without a clay liner, so the smoke ran directly against brick and lime mortar. Coal smoke is rich in sulfur, which combines with moisture to attack mortar joints. After a century of that, it is common to find eroded joints, gaps between flues that share a wall, loose bricks and a heavy layer of old soot.

Several coal flues often run side by side in one stack, separated only by a single course of brick called a wythe. When that brick has deteriorated, smoke from one flue can slip into the next, and into rooms on another floor. That is why every flue in an old coal chimney is evaluated on its own before any fireplace is used.

What an inspection looks at

A proper look at a coal fireplace starts at the firebox and works up to the crown. The goal is to answer three questions: is the firebox big enough and sound enough for the fuel you want, is the flue lined and intact, and is it the right size for that fuel.

• Firebox depth, height and width, and whether the lining is firebrick, thin brick or iron
• Whether there is a damper, a smoke chamber and a smoke shelf, or just an open throat
• Whether the flue is lined, and the condition of the liner or the bare brick
• The walls between adjacent flues, and any sign of smoke passing between them
• Clearance from the firebox and flue to wood framing, floor joists and trim
• The crown, cap and top of the stack, where water often enters

Options for bringing one back

What makes sense depends on the firebox, the flue and what you want from the fireplace. For a real wood fire, some fireboxes can be rebuilt in firebrick with more depth, along with a properly sized liner, a damper and a hearth extension that meets code. That is masonry work, and it is only possible where the opening and the space behind it allow it.

Many owners choose a gas insert made for small openings instead. It needs little depth, vents through a liner run up the old flue, and gives steady heat with no smoke in the room. An electric insert needs no venting at all and suits a fireplace that only needs to look alive.

Others keep the fireplace purely decorative. In that case the flue should be properly closed at the top with a cap or seal that still allows a little ventilation, and the opening sealed at the throat, so the chimney does not become a cold draft and a water path.

Coal grates, summer covers and original inserts

An original coal grate is a handsome piece worth keeping, but it was made for coal and does not turn the fireplace into a wood burner. Many old coal fireplaces also have a cast iron insert, an iron box with a grate and a front frame, which may be original to the house. Before lighting anything in one, check whether it was built for burning or has been altered for show, and whether the flue behind it is sound.

Decorative summer covers, the hinged or loose iron panels that close the opening, often hide a firebox that has not been used in decades. Behind them it is common to find fallen soot, old nests and loose brick on the floor.

Can you still burn coal?

Coal should only go into a fireplace or stove that was built and lined for it, and only where local rules allow it. Rules on what fuels may be burned, and where, vary by town and change over time, so ask your town's building or environmental office before burning anything other than wood in an old fireplace. This is general guidance, not legal advice.

Before the first fire

Treat any old coal fireplace as unused until it has been inspected from top to bottom, even if a previous owner says it worked. The first fire in a long-cold flue is the one most likely to find a blocked flue, a cracked wall between flues or a nest sitting on the smoke shelf.

We can tell you whether the firebox can be rebuilt for wood, whether a small gas insert fits, and what the flue needs to be safe, with upfront pricing and no hidden fees. That lets you decide between a working fire, a gas flame or a handsome iron front that stays cold.