What Is a Fireplace Insert? Why So Many Fireplaces Get Called One

A fireplace insert is a heater made to go inside a fireplace you already have. It sits in the old opening, a surround covers the gap around it, and a wood or direct vent gas insert vents through a new liner run up the existing chimney. That is the strict meaning. In stores, on product pages and in conversations with contractors, "insert" also gets used for built-in fireplaces, electric fireboxes, log sets and even wood stoves, so a lot of people end up shopping for the wrong thing. Here's where the mix-up comes from and how to sort it out before you buy.

What makes something an insert

Every true insert has three things in common.

1. A minimum fireplace opening. The spec sheet lists the smallest existing fireplace it will fit. The Majestic Ruby 35" gas insert needs an opening 36-5/8" wide at the front, 25-1/8" at the rear, 24-1/4" high and 15" deep. The Osburn 2000 wood insert needs 28-7/8" wide, 23-3/8" high and 15-3/4" deep.
2. The old chimney does the venting. Osburn's wood inserts call for a 6" listed liner run up the chimney, and the Ruby vents through a direct vent liner kit, such as Majestic's insert kits with termination caps. Electric and vent-free gas inserts don't vent at all.
3. A surround or faceplate. It covers the gap between the insert and the old opening. Majestic lists a front and a surround as required for the Ruby 35", starting with a 42" x 29" surround. The Osburn 2000 needs a door overlay, a faceplate and faceplate trims to be complete.

If what you're looking at lists framing dimensions instead of a minimum fireplace opening, it is a built-in fireplace, whatever it is called. For the side-by-side on cost, efficiency and fit, see Fireplace vs. Fireplace Insert.

Why the word gets misused

A built-in fireplace looks like an insert once it's finished

A zero clearance fireplace is a complete fireplace framed into a wall, with its own chimney or vent. Finished in stone, it looks just like an insert: a steel box behind glass doors. Compare two Osburn models. The Stratford II ($4,499) is a zero clearance fireplace: its spec sheet gives framing dimensions, 0" clearance to the enclosure at the back, sides and floor, and a 6" chimney at least 15' tall. The Osburn 2000 ($3,129) is an insert: its spec sheet gives a minimum fireplace opening, and it vents through a liner in the chimney you already have. Same brand, both behind glass, and two different products. Our guide to zero clearance fireplaces explains how they work.

Product names use "insert" for more than one job

Some products really can do both, and their names follow one use:

• The Modern Flames Redstone is sold as a "built-in electric fireplace insert." It plugs into a 120V outlet when it slides into an existing zero clearance wood-burning fireplace, and it is hardwired when it is recessed into a wall 10" deep.
• The Empire Loft VFLC28 is a "vent-free gas fireplace insert." It fits an existing wood-burning masonry or factory-built fireplace, or a framed wall with a 30 1/2" x 22 3/8" x 15" rough opening.

So the name tells you what a product can do, not what you need. Start from what you have: a fireplace or a blank wall.

Some wood stoves are inserts too

The Buck Stove Model 21NC ($2,191) and Model 91 ($4,047) install either way: freestanding as a stove, or with a trim kit as an insert in a masonry fireplace. That is why "stove" and "insert" overlap in so many listings.

Log sets get lumped in

An electric log set is the lightest option for an open fireplace, and it is often called an insert too. The Dimplex Revillusion 20" Plug-In Electric Log Set ($429.99) sets into a masonry opening and plugs into an ordinary outlet, and the back of the fireplace stays visible through the flame the way it does with an open grate, so the fireplace keeps its open look. The Napoleon Woodland ($629) also runs on a standard 120V outlet. See all electric log sets.

The fireplace you have may already be factory-built

Plenty of fireplaces are themselves zero clearance units: a steel firebox with a metal chimney. Putting an insert in one means putting one appliance inside another, and many inserts don't allow it. Most of the wood inserts we carry are made for masonry fireplaces only, including the Osburn Matrix, Inspire 2000-I and 3500, the Ironstrike and Empire Archway inserts, and the Buck Model 91. The True North TN20 ($2,546.14) is made for masonry and factory-built fireplaces. Some fireplaces rule it out on their side too: the Superior WCT6940 is for dry, seasoned wood only, not gas logs or a fireplace insert.

Insert, built-in or log set: what are you shopping for?

Prices at Dreamwood Living as of November 2026.

Five questions to ask before you buy anything called an insert

1. Does the spec sheet give a minimum fireplace opening, framing dimensions or both? The Ruby lists a minimum opening, the Stratford II lists framing, and the Empire Loft lists both.
2. Is my fireplace masonry or factory-built, and does the insert allow it? Check the insert's listing and the label on your fireplace.
3. How does it vent? A wood insert needs a liner up the chimney, a direct vent gas insert needs its liner kit, and electric and vent-free inserts need none.
4. What else has to be ordered with it? The Ruby needs a front and a surround, the Osburn 2000 a door overlay, faceplate and trims, and the Loft a surround.
5. Can I go back to burning wood? Not always. Empire says a fireplace converted for the Loft cannot go back to burning wood.

Frequently asked questions

What is a fireplace insert?

A heater made to fit inside an existing fireplace. It uses that fireplace's opening and, for wood and direct vent gas models, a new liner up its chimney, with a surround to cover the gap around the face.

How does a fireplace insert work?

It closes the open fireplace with a firebox behind glass. A wood insert burns in a sealed firebox, and on most models a blower pushes room air through the space around the firebox and back out the front. A direct vent gas insert like the Ruby 35" burns 24,500 to 35,000 Btu/hr and has a fan built in. An electric insert plugs in: the Orion V2 gives 5,000 BTU on a standard 120V outlet.

Is a zero clearance fireplace an insert?

No. A zero clearance fireplace frames into a wall and has its own chimney or vent. An insert goes inside a fireplace that is already there.

Is an electric fireplace an insert?

Some are and some aren't. The Modern Flames Orion V2 is built to slide into an existing fireplace. The Redstone works either way. The Napoleon Elevation Electric 36" is built-in only, fully recessed into a framed wall.

Can you put a fireplace insert in a prefab fireplace?

Only when both allow it. Among the models we carry, the True North TN20 wood insert, the Empire Loft vent-free gas inserts and the Modern Flames Redstone electric are made to go in factory-built fireplaces. Most of our wood inserts are made for masonry fireplaces only.

Do I need an insert or a new fireplace?

If you have a working fireplace and chimney you want to keep, an insert. If you have a blank wall or you are opening one up, a built-in fireplace. Our guide to fireplace vs. fireplace insert compares the cost of each.

Not sure which one you need?

Call us at 888-486-2909 with your fireplace's front width, rear width, height and depth, and the model number off its label if it has one. We will tell you whether you need an insert or a fireplace, and which ones fit. We are here 9am to 9pm CST. You can also browse all of our fireplace inserts.