Wood Burning Fireplace Inserts: Sizes, How to Measure and Chimney Liners

A wood burning fireplace insert is a wood stove built to sit inside an existing fireplace, usually vented through a stainless steel liner run up the chimney. Three questions decide whether one will work in your house: what kind of fireplace you have, whether the opening is big enough, and what the chimney needs. This guide answers each one with the published specs of the wood inserts we carry, which run from $2,191 for the Buck Stove Model 21NC to $4,639 for the Ironstrike Montlake 300.

The short answer

Most wood inserts are made for masonry fireplaces only; of the inserts we carry, the True North TN20 is the one that also goes into a factory-built fireplace. The opening has to meet the insert's minimum width, height and depth, and some also list a minimum rear width and a maximum lintel depth. Osburn, Ventis, Empire, Ironstrike and True North all call for a listed 6" chimney liner. Then budget for the faceplate or surround most inserts need to look finished, and size the insert to the space you want to heat.

Step 1: Check what kind of fireplace you have

This rules out more inserts than anything else. A masonry fireplace is built of brick or stone on site. A factory-built (prefab or zero-clearance) fireplace is a metal box framed into the wall. Here is what the manufacturers allow:

• Osburn: the Matrix 1900, Inspire 2000-I, 3500 and Matrix inserts are masonry only, and factory-built fireplaces are not permitted.
• Ironstrike: masonry fireplaces only. The manual for the Striker C160 states it must not go in a factory-built (zero-clearance) fireplace.
• Empire Archway: only in a code-compliant masonry fireplace with a lined masonry chimney built for solid fuel.
• Buck Stove Model 91: not for factory-built (zero-clearance) fireplaces.
• True North TN20 Wood Insert ($2,546.14): made for masonry and factory-built fireplaces.

If you have a factory-built fireplace and another insert won't go in it, the TN20 is the wood option here. Otherwise, look at EPA certified zero clearance wood fireplaces to replace the unit, or an electric insert, which needs no chimney.

Step 2: Measure the fireplace opening

Measure inside the firebox and write each number down:

1. Front width across the opening.
2. Rear width across the back wall. Masonry fireboxes often narrow toward the back, and some inserts list a minimum rear width: 22-1/2" for the Ironstrike Montlake 230 and 27-1/4" for the Montlake 300.
3. Height from the hearth floor to the top of the opening.
4. Depth from the front of the opening to the back wall.
5. Lintel depth: how far the top of the opening (the lintel) extends back before the firebox opens up. Ironstrike lists a maximum: 4-3/4" for the Striker C160 and 5-3/8" for the Montlake inserts, without an offset box or smoke deflector.
6. The face around the opening, for the faceplate or surround to cover (Step 4).
7. The hearth and mantel. The Montlake 230 needs a hearth extension 16" in front of the door opening and 8" to each side, and a mantel at least 36-3/4" above the base of the insert. The Montlake 300 needs 18" in front and a mantel at least 48-3/4" up.

Then compare with the minimum opening for each insert. If you need a fresh air intake, Osburn says to add at least 4" to the minimum width on the 2000 and Matrix inserts.

Prices at Dreamwood Living as of November 2026. The Montlake figures are the minimum front width, height and depth, with the minimum rear width in brackets. The Osburn Matrix can go into a shallower opening, 17-5/8" or 15-5/8" deep, with its projection kit. See all wood fireplace inserts.

The width you need climbs with the size of the insert. The smallest inserts here fit openings as narrow as 23-1/4" to 25", while the 3.5 cu ft Osburn 3500 and Ventis HEI350 need 31". The Ventis HEI90's tapered top and sides let it slip into openings as small as 19" high by 25" wide by 15-1/2" deep.

Size for the room, not only the opening

Once you know which inserts fit, choose by the space you want to heat, the same way you would choose a wood stove. The ratings run from 250 to 1,200 sq ft on the Osburn Matrix 1900 up to 2,000 to 3,000 sq ft on the Montlake 300. A bigger firebox also burns longer: the Osburn 1700 insert is rated for up to 7 hours, the 2000 for 8 and the 3500 for 10.

Step 3: The chimney liner

The Osburn, Ventis, Empire, Ironstrike and True North inserts all call for a listed chimney liner from the insert up the chimney:

• Osburn: a 6" listed liner (UL 1777), at least 12 feet tall.
• Ventis: a 6" listed liner (UL 1777); 12 feet minimum on the HEI90.
• Empire Archway: a continuous 6" stainless steel liner listed to UL 1777.
• Ironstrike: a 6" stainless steel liner; for the Montlake, from the insert to the top of the chimney.
• True North TN20: a 6" listed stainless steel liner, rigid or flexible. Pacific Energy recommends a full liner to the top of the chimney, and in the USA also permits a direct connection with the liner sealed into the first flue tile.
• Buck Stove Model 21NC and Model 91: the chimney requirements are in the manual. The 21NC has a 6" flue and the 91 an 8" flue, with 6" and 8" offset adapters available.

We carry the National Chimney M-Flex Wood-Burning Insert Basic Liner Kit, a 316 stainless steel liner listed to UL 1777. It comes in 6" or 8" and in 15, 25 or 35 foot lengths, from $658.92 (15 feet, 6") to $1,439.54 (35 feet, 8"); the 25 foot, 6" kit is $947.24. Each kit includes an EZ clamp stove adapter, a rain cap and a 13" x 13" top plate. To pick a length, measure from the fireplace floor to the top of the chimney and allow for the connection at the insert. Osburn lists an offset liner adapter, and Ventis offset and hook-up liner adapters, for their inserts. Whether the liner needs insulation depends on your chimney and local code, so ask your installer and check the insert's manual.

Step 4: The faceplate or surround

A wood insert usually needs a faceplate or surround to cover the gap between the insert and the fireplace opening, and on most models it is ordered separately:

• Osburn 1700 and 2000: need a door overlay, a faceplate and faceplate trims to be complete, with a regular 29" x 44" or large 32" x 50" faceplate. The 2000 can instead take an optional 32" x 50" cuttable faceplate, and then only the door overlay is required.
• Ventis HEI240: one faceplate required, regular 29" x 44" or large 34" x 50". The HEI90 takes a 26" x 42" faceplate.
• Empire Archway 1700: a door overlay and a surround (29" x 44" or 32" x 50") are required.
• Ironstrike Montlake 230: one top and one surround panel kit sized to the opening, from 26-1/2" x 41" to a trimmable 33" x 48".
• Ironstrike Striker C160: surround panels are required, in overall sizes from 26-1/2" x 40" to 30-1/2" x 48".
• True North TN20: a standard 27" x 38" surround is included, with a 32" x 48" oversize backing plate available for bigger openings.

Compare the face measurement you took with these sizes. If your fireplace face is larger than the biggest faceplate made for an insert, call us before you order.

Power for the blower

Most of these inserts come with a blower, and it needs an outlet near the fireplace. The True North TN20's blower runs on 115V at 0.5 A with a grounded three-prong plug, and the Ironstrike Montlake's on 120V at 0.8 A. The Ironstrike Striker C160 and Performer C210 list a 160 CFM blower as an option.

Insert or wood stove?

An insert sits inside the fireplace and vents up the chimney you already have. A freestanding stove sits on the hearth or floor in front of it. The Buck Stove Model 21NC and Model 91 can do either: freestanding as a stove, or with a trim kit as an insert in a masonry fireplace. For more on the difference, see fireplace vs fireplace insert and types of wood burning fireplaces.

Frequently asked questions

Do I need a chimney liner for a wood burning insert?

Yes, for the Osburn, Ventis, Empire, Ironstrike and True North inserts we carry. Osburn, Ventis, Empire and Ironstrike call for a listed 6" liner, and Osburn and the Ventis HEI90 require it to be at least 12 feet tall. True North recommends a full liner to the top of the chimney for the TN20. For the Buck inserts, follow the chimney requirements in the manual.

Can a wood insert go in a prefab fireplace?

Only if the manufacturer allows it. Of the inserts we carry, the True North TN20 is made for masonry and factory-built fireplaces. The Osburn, Ironstrike, Empire Archway and Buck Model 91 inserts are for masonry fireplaces only.

What size wood burning fireplace insert do I need?

Two sizes matter. First, your opening has to meet the insert's minimum width, height and depth, plus the rear width and lintel depth where they are listed. Second, the insert's heating area should cover the space you want to heat. Among inserts that fit, pick the one rated for your square footage.

What is the largest wood burning fireplace insert?

Of the inserts we carry, the Osburn 3500 and Ventis HEI350 have the most output at 110,000 BTU/h, with 3.5 cu ft fireboxes rated for 1,000 to 2,700 sq ft. The catalytic Buck Stove Model 91 has the largest firebox at 4.4 cu ft and is rated for up to 3,200 sq ft. The Ironstrike Montlake 300 is rated for 2,000 to 3,000 sq ft.

Do wood inserts come with a blower?

Most of ours do, from 90 CFM on the Ventis HEI90 and Osburn Matrix 1900 to 176 CFM on the Osburn Inspire 2000-I and Matrix 2700. On the Ironstrike Striker C160 and Performer C210, the blower is optional.

How much does a wood burning insert cost?

The inserts we carry run from $2,191 to $4,639. Add the faceplate or surround most models need, and a liner kit, from $658.92 for 15 feet of 6" liner. Installation is separate.

Send us your measurements

Call us at 888-486-2909 with your fireplace's front width, rear width, height and depth. Tell us whether it is masonry or factory-built and how tall the chimney is, and we will tell you which inserts fit and what to order with them. We are here 9am to 9pm CST.