Fireplace Inserts

Choosing a fireplace insert

Measure the opening before you shop

Every insert publishes a minimum fireplace opening, and this is the gate every purchase has to clear. You need four numbers from your existing masonry firebox: height, width at the front, width at the back, and depth from the face to the back wall. The rear width catches people out, because most masonry fireboxes taper inwards and it is frequently the dimension that rules a model out. Depth is usually the tightest constraint of all. Take all four before you fall for a particular model.

The chimney is the real cost difference

The appliances are not as far apart in price as the installations are. A wood insert needs a continuous insulated stainless liner running the full height of the chimney, with a block-off plate at the damper — often the largest single line on the job after the insert. A direct vent gas insert needs a liner system too, usually either two flexible liners or a coaxial one, though it is typically a lighter job than a wood liner. A vent-free gas insert needs no liner at all. An electric insert needs nothing done to the chimney whatsoever; the damper can simply be closed and sealed. Price the liner and labour alongside the appliance, because that total is the only fair comparison.

Have the flue looked at before you commit

An insert seals the fireplace up, so anything wrong behind it becomes much harder to reach afterwards. A camera inspection tells you whether the flue is sound, what its true height is — which drives the liner cost — and whether there are offsets that make lining awkward. On an older chimney this is worth doing before you order anything, not after the insert is sitting in your hallway.

Gas: direct vent or vent-free

A direct vent gas insert is sealed behind glass and vents through a liner up the existing chimney, drawing its combustion air from outside. It is efficient, generally permitted in bedrooms, and the default choice for most people. A vent-free gas insert burns without any flue connection at all, which makes it the cheapest gas installation by a distance, but the combustion products stay in the room, output is tied to room volume, and many jurisdictions restrict or prohibit them in bedrooms and bathrooms. Check local code before choosing vent-free.

Electric: the one with no constraints

An electric insert needs no liner, no gas line and no venting, which makes it the cheapest and fastest of the three to install and the only one that works when the chimney is unusable, blocked or shared. It is also the only option for many condos and apartments. The trade is heat: around 5,100 BTU on a standard circuit, which takes the chill off a room but will not heat it, and that figure does not rise with the size of the unit. If you want the fireplace to look alive and cost almost nothing to fit, this is the answer.

Wood: the most heat, and the most work

A wood insert produces the most heat of the three and keeps producing it in a power cut, which is why people in cold or outage-prone places still choose it. In exchange it wants an insulated liner, seasoned wood, somewhere to store that wood, loading and tending, and an annual sweep. Look for an EPA certified model, which burns far cleaner and extracts more heat from the same wood than an older appliance would.

Size it to the room, not the house

Inserts are sized by firebox volume on wood and by BTU on gas, and in both cases the temptation is to buy more than you need. An oversized wood insert has to be run damped down, which burns dirty and glazes the glass; an oversized gas insert spends the winter on its lowest setting with a thin-looking flame. Remember too that an insert heats the room it is in far better than the rooms beyond, so size it for that room and let your existing heating handle the rest.

Budget for the surround as well

Almost every insert needs a surround or faceplate to cover the gap between the appliance and the fireplace opening, and they come in set sizes — commonly around 29" x 44" or 32" x 50" — so the one you need depends on your opening. Some are trimmable and some are not. Add a blower if the model offers one, since an insert sits inside masonry that will happily absorb the heat you paid for, and a fan makes a noticeable difference to what actually reaches the room.

Fireplace insert FAQs

What is a fireplace insert?

It is a sealed firebox designed to fit inside an existing masonry fireplace, turning an open hearth into a closed, controlled appliance. Gas and wood inserts vent through the existing chimney using a liner; electric inserts need no venting at all. The appeal is that you reuse the fireplace, hearth and chimney you already own, so there is no construction and no floor space lost.

Will an insert fit my fireplace?

Measure first: height, front width, rear width and depth of the masonry opening. Every model publishes a minimum fireplace opening in its manual, and your four numbers have to clear it. Rear width and depth are the two that most often rule a model out, because masonry fireboxes taper towards the back and are shallower than people assume.

Do I need a chimney liner for a fireplace insert?

It depends entirely on the fuel. A wood insert needs a full insulated stainless liner running the height of the chimney. A direct vent gas insert needs a liner system as well, though usually a lighter one. A vent-free gas insert and any electric insert need no liner at all. Since the liner is often the biggest cost after the appliance, this single question drives most of the price difference between the three options.

Which type of insert is cheapest to install?

Electric, by a wide margin, because nothing happens to the chimney and there is no gas line — frequently just a dedicated circuit. Vent-free gas comes next. Direct vent gas is higher because of the liner and the gas line. Wood is usually the most expensive to install, since the insulated liner is a substantial job in its own right. Compare installed totals rather than appliance prices, because the ranking often reverses.

Can I put an insert into a prefab or zero-clearance fireplace?

Only if both the insert and the fireplace are specifically listed for that combination, and most are not. A factory-built metal fireplace is a tested assembly, and fitting an appliance it was never certified with voids its listing and creates a real hazard. Some manufacturers do list particular inserts for particular prefab fireplaces. Check the manual and your fireplace's data plate, and have an installer confirm before ordering.

Do fireplace inserts save money on heating?

A gas or wood insert usually does, because an open masonry fireplace runs at roughly 5 to 15% efficiency and pulls heated household air up the chimney while it burns — it can leave a house colder overall. A sealed insert runs in the region of 70 to 85%, so the room it serves genuinely warms and your central heating works less. An electric insert will not save on heating, since it produces little heat; its appeal is the look and the near-zero installation cost.

Gas, electric or wood — which insert should I choose?

Choose gas if you want real heat with no work and you can get a gas line to the fireplace. Choose electric if the chimney is unusable or shared, you are in a condo, or you mainly want the look for the lowest possible cost. Choose wood if you want the most heat, you have somewhere to store fuel, and you want a fireplace that still works when the power is out. The chimney usually decides it before taste does.

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