Is a Fireplace Insert Better Than an Open Fireplace?

How an open fireplace behaves

An open fire pulls a large volume of room air into the opening and sends it up the chimney along with the smoke. You feel strong radiant heat sitting close to the flames, but warm air from the rest of the room is drawn up the flue too, and cold outside air seeps in through windows, doors and gaps to replace it. Rooms away from the fireplace can actually get cooler while it burns.

That is the trade-off. An open fireplace is about atmosphere: the crackle, the smell, the open view of the flames. It was not designed as an efficient heater, and in older homes built around a coal grate or a shallow wood firebox, it often draws a lot of air for the warmth it gives back.

How an insert works

An insert is a steel or cast iron firebox with a sealed glass door that slides into the masonry fireplace. The air feeding the fire is controlled, so a wood fire burns slower and more completely, and a gas flame burns at a set rate. Heat moves into the room through the glass and the metal face, and many models add a blower that pushes warm air out from around the box.

The insert connects to a liner that runs up inside the existing chimney to its outlet. A decorative surround panel closes the gap between the insert and the fireplace opening, so room air is no longer pulled up the old flue. The masonry around it stores some heat and releases it slowly after the fire dies down.

Side by side

The three options differ less in looks than in how they fit your routine and your chimney:

Wood insert or gas insert

A wood-burning insert gives a real fire with much more usable heat than the open fireplace it replaces, and longer burns between reloads. You still buy, store and carry wood, keep the fuel dry and seasoned, carry out ash, and keep the liner swept, because a slower-burning fire can still deposit creosote if the wood is wet or the air is turned down too far.

A gas insert runs from a switch, remote or thermostat, with no wood and no ash. It needs a gas line brought to the firebox by a licensed installer, and permit rules for that work vary by town. The flame looks close to a wood fire but is more uniform. Both types are vented appliances, and their venting belongs in the same yearly chimney inspection that NFPA 211 sets out.

The liner an insert needs

An insert is designed to vent through a liner sized to its own outlet, as the manufacturer's installation instructions specify. The original clay flue in a fireplace chimney was sized for a large open opening, so it is usually far bigger than an insert's outlet. Venting a small appliance into that oversized flue lets the exhaust cool and slow down, which hurts draft and lets deposits or condensation build up. Wood inserts commonly use a stainless steel liner; gas inserts vent through the system their maker lists, often with separate paths for exhaust and fresh air.

The liner usually runs from the insert's collar to the outlet in one continuous length, with a cap at the outlet. The damper is typically removed or locked open to let the liner pass, and the smoke chamber around it is closed off.

What the existing fireplace must provide

Not every fireplace can take every insert. Before choosing a model, the fireplace is measured and the chimney inspected, checking these points:

• Firebox width, depth and height, front and back, against the insert's required dimensions
• Hearth extension size and the clearance to the mantel and trim the insert's manual sets
• Sound firebox, smoke chamber and chimney structure
• A flue that serves only the fireplace, not a boiler or water heater as well
• Room at the chimney outlet for the liner and cap
• An outlet nearby for a blower, and a gas supply route for a gas model

Older homes and shared chimneys

In many houses across New York, New Jersey and the Philadelphia area, one masonry chimney carries more than one flue, and over the decades the fireplace flue was sometimes handed to an oil or gas boiler. An insert needs its own flue. If the fireplace flue is already in use by a heating appliance, the options are finding a free flue in the stack, venting the heating appliance another way, or choosing an electric unit that needs no flue at all. That question is settled at the inspection, before any money is spent on equipment.

Size is the other common hurdle. Many late nineteenth and early twentieth century rowhouses and brownstones have fireplaces originally built for coal, with shallow fireboxes and small openings. Most wood inserts need more depth than those fireboxes offer. Some of these openings can take a gas insert designed for shallow spaces, and others are better suited to an electric unit or to restoration as an open fireplace with a smaller fire.

Which one suits your home

The deciding factor is how you actually use the fireplace. An insert adds the unit, a liner and installation, and a gas insert adds the gas line, so the investment pays back in comfort when the fireplace is used often. A few patterns hold for most households:

• Occasional fires for atmosphere: keep the open fireplace in good repair
• Real heat on cold nights, with wood on hand: a wood-burning insert
• Heat on demand with no wood or ash: a gas insert
• A cracked or unlined flue that needs a liner anyway: a good time to consider an insert
• No usable flue: an electric insert, which plugs into an outlet