Can You Convert a Wood Fireplace to Gas?

Two ways to put gas in a wood fireplace

Almost every conversion of a masonry fireplace comes down to one choice: keep the fireplace open and put gas logs in it, or close it up with a gas insert. The difference is not only looks. It decides how much heat you get, what the chimney needs, and how much work the job involves.

A rough rule: if the fireplace is a centerpiece you light for company and holidays, logs often fit. If the room is chilly every winter and you want the fireplace to carry part of the heating load, an insert is the conversion that does that. Some owners of multi-fireplace brownstones do both, logs in the front parlor and an insert in the room they actually live in.

Vented gas logs

A vented log set is a gas burner with ceramic logs arranged on top, sitting where the grate used to be. The fireplace stays open, and the flames are tall and yellow so they look like a wood fire. Because the logs produce exhaust, the flue has to stay open whenever they burn. The damper is usually fitted with a clamp or stop so it cannot close completely, as the log set's instructions require.

Vented logs suit someone who wants the look and the ritual of a fire on winter evenings without hauling wood or cleaning ash. They are not a heating system. Like a wood fire, most of their warmth leaves through the chimney, and the open damper lets warm room air escape too.

Gas inserts

A gas insert is a sealed firebox with a glass front that slides into the existing masonry firebox. Most current inserts are direct vent: they draw combustion air from outside and send exhaust outside through a pair of liners, or a single liner with an inner and outer pipe, running up the old flue to a fitting at the top. The room air never mixes with the fire.

Because the combustion is sealed and the unit is built to transfer heat into the room, an insert can warm a living room or a parlor floor on its own. It is the conversion that changes the fireplace from a feature into a heater. A metal surround panel covers the gap between the insert and the brick opening.

Inserts are sized to the opening, so the firebox is measured carefully before a unit is chosen. Shallow or unusually shaped fireboxes, including old coal fireplaces, narrow the list of models that fit.

A note on ventless logs

Ventless or vent-free gas logs burn without a chimney, releasing their combustion products into the room. Whether they are allowed, and where, depends on local codes, and some areas restrict them. If you are considering them, ask your local code office and read the manufacturer's instructions closely. Any gas appliance in the house calls for working carbon monoxide alarms, and with vent-free units that matters even more.

What the chimney needs first

Before any gas appliance goes in, the chimney is swept and inspected. Years of wood fires leave creosote in the flue and the smoke chamber, and that residue does not just sit quietly once gas logs are running: it can give off a strong smell, and in an insert installation it is in the way of the new liner. The flue, crown, cap and firebox should all be in sound condition.

In older homes across the region, the inspection often turns up something to fix first: cracked flue tile, a crown letting water in, loose firebrick or a damper rusted in place. In homes where a boiler or water heater shares the chimney, each appliance still needs its own flue, and a gas fireplace does not get vented into a flue already serving another appliance.

• Creosote removed from the flue and smoke chamber
• Flue tile or liner checked for cracks and open joints
• Damper working, or clamped as the log set requires
• Crown and cap sound so water stays out of the new system
• Firebox clear of loose or broken brick

Running the gas line

A gas line is run from the existing supply to the fireplace, ending in a shutoff valve that can be reached easily. Gas piping is work for a licensed plumber, and it usually involves a permit and an inspection. The route matters: a short run from a basement directly below the fireplace is simple, while a line that has to climb to a second-floor parlor in a brownstone, or cross finished ceilings, is a bigger job.

Homes heated with oil sometimes have no gas service at all. Then the question becomes whether the utility can bring service to the house, which is a separate conversation with them.

Factory-built wood fireplaces

If the fireplace is a metal factory-built unit rather than brick, the conversion has to follow that unit's manufacturer instructions. Some models allow specific gas log sets or inserts, and some do not allow conversion at all. The label inside the firebox, or on the frame behind the screen, identifies the model and points to the instructions.

If the label is missing or unreadable, the safe assumption is that the unit cannot be converted until its make and model are confirmed. Fitting gas into a factory-built firebox that was not tested for it can overheat the metal casing and the framing around it.

What shapes the cost

The biggest single choice is logs or an insert. After that, the price depends on the specific house and what the inspection finds.

• Logs versus insert, and the size of the unit
• Length and difficulty of the gas line run
• Whether a new liner is needed, and how tall the chimney is
• Any repair to the flue, crown, firebox or damper found first
• Finish work around the opening, and permits

Living with a gas fireplace

Gas burns cleaner than wood but still produces combustion gases, including carbon monoxide. The chimney or vent should be inspected every year, as NFPA 211 calls for with all chimneys and vents, and the unit serviced as its manufacturer recommends. Nests, debris and fallen tile can block a gas flue just as they block a wood one. Keep carbon monoxide alarms on every floor; if one sounds, head outside first, then phone 911 or your utility.

Our own crew handles the chimney side: the sweep, the inspection, the liner and the top fitting, coordinated with the plumber who runs the gas. You get the chimney work in writing after we have looked at it.