Gas Insert vs. New Direct Vent Fireplace: Which Is Right for Your Home?

Most of the fireplace calls we get from Brooklyn brownstones, Queens two-families, Long Island colonials and Westchester Tudors start the same way: there is an old masonry wood fireplace in the living room, nobody has lit it in years, and the owner wants gas. From there the conversation splits. You can slide a gas insert into the existing firebox and vent it up the chimney, or close off the old fireplace and build in a new direct vent gas fireplace with its own vent. This guide covers what each one is, where the money goes, how they heat and look, and which we recommend in which situation. A cheaper third option gets its own section.

What is a gas insert?

A gas insert is a sealed steel firebox, with its own glass front, burner and log set, built to slide into the opening of an existing wood-burning fireplace. It is a direct vent appliance, just packaged differently. Instead of a rigid coaxial pipe, it vents with two flexible metal liners (co-linear venting) that run up the old chimney: one carries exhaust out, the other brings combustion air down. A cap at the top of the chimney ties the two together and seals off the old flue.

The insert is smaller than the masonry opening it goes into. A surround (also called a shroud or faceplate) covers the gap between the insert and the brick, and a decorative front finishes the face. Because the insert sits inside non-combustible masonry, it can run hotter than a framed-in fireplace and most models are built as serious heaters: steel tube heat exchangers, a blower, and 25,000 to 35,000 BTU burners are typical.

Real examples from our floor: the Majestic Ruby 30 runs 22,890 to 32,700 BTU on natural gas with IntelliFire Touch ignition, a variable fan and the RC400 touchscreen remote included. The Napoleon Oakville X3 is rated at 30,000 BTU with Proflame II electronic ignition and its blower in the box. The Kozy Heat Chaska 29 is a compact 30,000 BTU unit that fits small openings and still posts about 74 percent steady-state efficiency. The Montigo Illume DVCP34 modulates from 21,000 to 32,000 BTU and ships with its 3 inch and 4 inch co-linear flex kit. Kingsman's IDV26, IDV34 and IDV44 cover small, medium and large openings, with millivolt or Proflame II electronic ignition offered across the series.

What is a direct vent fireplace?

A direct vent fireplace (often called a zero-clearance or built-in fireplace) is a complete factory-built unit designed to be framed into a wall with ordinary lumber. It has its own insulated outer shell, so it needs no masonry at all. It vents through a rigid coaxial pipe, one tube inside another, that runs out through an exterior wall or up through the roof to a cap. Exhaust goes out the inner pipe; combustion air comes in through the gap between the pipes.

In a house with an existing masonry fireplace, one of three things happens to the old one: we demolish the masonry and frame the new unit in its place, we build the new unit beside the old opening and close the old one off, or the new fireplace goes on a different wall and the old one stays as a niche. The new unit does not use the chimney.

The payoff is freedom. You can choose a 36 inch traditional box like the Napoleon Ascent 36 or Kozy Heat Bayport 36, a high-output unit like the Majestic Marquis II, or a 48 to 72 inch linear like the Napoleon Ascent Linear Premium 46 or Montigo Distinction 48. None of those fit inside a typical 36 by 28 inch masonry opening.

How do they compare side by side?

Where does the cost go?

We do not print prices here because they move, but the shape of the budget is predictable and it is different for the two paths.

Insert jobs are driven by three things: the insert plus its required surround and front, the liner kit (a three-story brownstone chimney needs a lot more flex than a ranch), and the gas line. If the fireplace never had gas, running a new line from the meter is often the biggest variable. Chimney repair is the wild card, but a crown patch or new cap is modest next to a full rebuild.

Direct vent fireplace jobs are driven by construction. The unit and vent kit are only part of it. You are paying a carpenter to frame, a demo crew if the old masonry comes out, a tile or stone contractor for the non-combustible facing, drywall and paint, and possibly an electrician. A roof termination adds roofing. The result is a new focal wall, and the cost reflects that.

Our rule of thumb: with a good chimney, the insert path is usually the less expensive of the two by a meaningful margin, because so much of the structure is already there. When the chimney needs major work or the masonry is coming out anyway, the gap narrows fast and the design freedom of a new unit starts to look like the better spend.

Which heats better?

Both are sealed combustion appliances, and both are far more efficient than the open wood fireplace you are replacing, which pulls heated room air up the flue whether or not a fire is lit. Inserts have a structural edge: compact boxes with the burner close to the glass, a heat exchanger wrapped tightly around the firebox, and a blower on nearly every model. That is why a 30,000 BTU insert like the Oakville X3 or Chaska 34 can carry a 400 to 600 square foot living room through a Northeast winter evening.

A traditional direct vent fireplace in the same BTU class heats about as well. A large linear often does not, because the burner is spread across a wide, shallow box and much of the energy goes into the flame picture. If you are choosing a new unit for heat, pick a heater-rated traditional box or a linear with a heat management kit.

Published numbers to anchor on: the Chaska 29 lists 74 percent steady-state efficiency on natural gas with the log set; the Bayport 36 built-in lists 71 percent. Blower noise is the most common complaint in owner reviews for either category; get variable speed and plan on running it at low or medium.

What can you change about the look?

An insert keeps whatever you already have around the fireplace: the marble mantel in a prewar co-op, the brick in a Bay Ridge two-family, the carved wood surround in a Larchmont colonial. What changes is inside the opening. You choose the surround size (standard or custom cut), a front (clean screen, mission, arched, picture frame, cast iron), interior panels (brick, herringbone, reflective black glass) and media (oak, birch or driftwood logs, or glass and stones on contemporary models). Majestic's Trilliant 30 offers five front designs; the Napoleon Rosedale 3 adds arched faceplates for older openings.

What an insert cannot do is change the proportions. If the opening is 36 inches wide, the fire will be about 26 to 30 inches wide. If you want a 60 inch ribbon of flame under a floating TV, that is a new direct vent fireplace and a new wall.

A direct vent fireplace starts from zero, which cuts both ways. The whole wall is yours to design, and it has to be designed: facing material, mantel height and clearance, where the cap lands on the exterior. Our mantels and non-combustible shelves cover the finishing piece.

Is my chimney good enough for an insert?

An insert does not need the chimney to draft on its own; the liners handle that. It does need the chimney to be structurally sound and clear enough to run two flex liners from the firebox to the top. Before we quote an insert we want to know:

• Is the flue open end to end? Offsets, collapsed tiles, old bird screens, or a flue that was bricked over when a boiler was replaced all stop a liner.
• Is the crown and top of the chimney sound? The termination cap mounts there, and a crumbling crown lets water in around it.
• Is the flue shared? In some older NYC buildings a fireplace flue was tied into or runs beside a heating flue. A shared flue is a no.
• Is the damper removable? The liners pass through the damper opening. We usually remove the plate or lock it open; a cast damper that will not budge is a small job, but it is a job.

A camera inspection by a certified chimney sweep is worth doing before you commit. It also tells you whether the cheaper vented gas log route is on the table.

If the chimney fails, you either repair it (relining, crown work, rebuilding above the roofline) or walk away from it and build a direct vent fireplace that vents out the wall. In a detached Long Island or Westchester house with an exterior chimney that is leaning or spalling, the second choice is often the smarter one.

What about vented gas logs?

A vented gas log set is a burner and ceramic logs that sit on the grate of your open masonry fireplace. There is no glass, no liner and no sealed box. The chimney damper is clamped permanently open and the fire vents up the flue just like a wood fire did. The Napoleon Fiberglow and the Hargrove Charred Series are the ones we install most.

The appeal is cost and simplicity: no construction, no surround, battery or millivolt control, and the most realistic open flame of the three. The catch is heat. With the damper open, a vented log set loses most of its output up the chimney and pulls room air with it. Treat it as decorative even though the burner is rated at 50,000 BTU or more. It also depends on a chimney that drafts well, so the same inspection applies.

Vented log sets are legal in New York City in an existing, grandfathered wood-burning fireplace with a working chimney. Vent-free log sets are a different product and are not permitted in NYC, so if you shop our log set collection, stay on the vented side for any address in the five boroughs.

What are the NYC rules?

Three local rules push most city customers toward the insert.

Your old wood fireplace is grandfathered; a new one is not allowed. Local Law 38 of 2015 (Administrative Code Section 24-149.2, effective May 6, 2016) says no new fireplace may be operated unless it runs solely on natural gas or renewable fuel. Existing wood fireplaces may keep burning seasoned wood under 20 percent moisture. An insert keeps the original structure intact and converts it cleanly to gas, which is the path most co-op and condo boards are already comfortable with.

Vent-free is prohibited. The NYC Fuel Gas Code does not allow unvented gas room heaters or vent-free fireplaces and log sets. Every option in this guide (insert, direct vent fireplace, vented log set) is a vented appliance and is permitted. A vent-free insert advertised as a no-chimney solution is not an option inside the five boroughs.

Gas work needs a licensed master plumber. Under the NYC Fuel Gas Code, gas work must be done under the supervision of a DOB-licensed master plumber, and since January 1, 2020 anyone doing the work must hold a Master Plumber License or a Gas Work Qualification. Our crews install the insert, liner and finishing; the gas connection is done by a licensed master plumber under permit. Boards will ask for the permit and license number.

Outside the city, in Nassau, Suffolk, Westchester and New Jersey, the wood-burning rule does not apply, but the chimney logic is the same. Vent-free is legal in most of those areas; we still recommend vented for a primary living space.

Our recommended models

These are the units we quote most for masonry conversions, chosen by opening size, heat output and what ships in the box. Inserts first, then the two alternatives when the chimney is not an option or the budget is.

Gas inserts

Best OverallMajesticRuby 30 Gas InsertIt fits the common 36 inch opening, modulates from 22,890 to 32,700 BTU, and ships with the fan and RC400 remote, so there is nothing to add.View details →Best for HeatNapoleonOakville X3 (GDIX3N-1)A 30,000 BTU burner with the blower in the box is what carries a 400 to 600 square foot colonial living room through a January night.View details →Best for Small SpacesKozy HeatChaska 29 Gas InsertIt fits the shallow, narrow fireboxes in brownstones and prewar apartments and still posts about 74 percent efficiency.View details →Best ValueKingsmanIDV34 Direct Vent InsertCeramic glass, millivolt or Proflame II, and three surround styles at a price that leaves room for the liner and gas line.View details →Best PremiumMontigoIllume DVCP34 Large InsertThe 35 foot co-linear flex kit is in the box and the 21,000 to 32,000 BTU range covers big Long Island and Westchester openings.View details →Best for Older OpeningsNapoleonRosedale 3 (RD3N)The arched faceplate option solves the rounded prewar fireplace openings that square surrounds never quite cover.View details →

If the chimney is out, or the budget is tight

Best Built-In AlternativeNapoleonAscent 36 Direct Vent FireplaceWhen the chimney is out of the picture, this 36 inch box frames into a standard wall and vents out the side of the house.View details →Best Budget OptionNapoleonFiberglow Vented Log SetFor a working chimney and a few fires a year, it gives an open flame with no construction and battery control.View details →

Gas InsertsAll Fireplace InsertsDirect Vent Gas FireplacesGas Log SetsAll Gas Fireplaces

Which should you choose?

For the typical Brooklyn, Queens, Long Island or Westchester house with an old wood fireplace and a chimney that passes inspection, we recommend a gas insert: the Majestic Ruby 30 or Napoleon Oakville X3 for a standard opening, the Kozy Heat Chaska 29 for a small one. Build a new direct vent fireplace when the chimney fails or the design calls for a linear. Pick a vented log set only if you have made peace with it being decorative.

Frequently asked questions

Can a gas insert go into any wood-burning fireplace?

Into most masonry fireplaces with a sound, unobstructed chimney, yes. The opening has to be at least as large as the insert's minimum framing dimensions in width, height and depth, and two flex liners have to be able to run from the firebox to the top of the chimney. Factory-built (prefab) wood fireplaces are a case-by-case question; some are listed for specific inserts and many are not.

Does a gas insert need a chimney liner?

Yes. A direct vent gas insert uses co-linear venting: two flexible liners, typically 3 inch, or 3 and 4 inch depending on the model, that run the full height of the chimney and connect to a cap at the top. The old clay flue is not used as the vent.

Which heats better, a gas insert or a direct vent fireplace?

In the same BTU class, an insert usually heats a little better because it is a compact firebox with a blower and heat exchanger built in. A heater-rated traditional direct vent fireplace comes close. A large linear direct vent fireplace generally heats less for its size because the design favors the flame view.

Can I keep my existing mantel with a gas insert?

Usually yes. The insert sits inside the firebox and a surround covers the gap to the masonry, so the mantel, hearth and facing stay as they are. Check the insert's clearance to the mantel in the manual; some combinations need a heat shield.

Are vented gas logs a good heat source?

No. A vented log set burns with the damper clamped open, so most of the heat goes up the chimney along with room air. It is the most realistic open flame and the least expensive option, but treat it as decorative.

Can I install a gas insert or gas fireplace in New York City?

Yes. Inserts, direct vent fireplaces and vented log sets are all vented appliances and are permitted. Vent-free gas products are not allowed under the NYC Fuel Gas Code. The gas connection must be done by or under a DOB-licensed master plumber with a permit, and co-op and condo boards will want to approve the work.

Does a gas insert work during a power outage?

Millivolt models run with no electricity at all. Electronic ignition models from Majestic, Napoleon and Kingsman include battery backup for the valve so the fire lights without power. The blower and accent lights do need power.

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Written by the NYC Fireplaces & Outdoor Kitchens team. Last reviewed October 2026. We sell, install and service the products discussed here.

Sources:Kozy Heat: Direct Vent Insert vs. Direct Vent Fireplace, Kozy Heat Chaska 29 specifications, Napoleon Oakville X3, Napoleon Rosedale 3, Napoleon: How Direct Vent Fireplaces Work, Regency: Fireplace Insert vs. Direct Vent, NYC Administrative Code 24-149.2 (Local Law 38 of 2015), NYC DOB gas work service notice, 2022 New York City Fuel Gas Code. Specifications change; always confirm with the manufacturer's current installation manual.