Double-Sided Fireplace Insert: Complete Guide for Homeowners

See-through fireplaces look stunning, framing a fire between a living room and dining room or a bedroom and bath. They are also notoriously inefficient and prone to smoking, because an opening on both sides lets drafts blow straight through the firebox. A double sided fireplace insert promises to fix both problems, but the options are narrower than most homeowners expect, and the right answer depends on the fireplace you already have. This guide explains what is actually available, how each type is vented, what installation costs, and the safety rules that apply.

What a Double Sided Fireplace Insert Actually Is

A standard fireplace insert is a sealed firebox that slides into an existing masonry or factory-built fireplace and vents through a new liner in the chimney. A double-sided, or see-through, insert does the same thing with glass on both faces. Here is the catch: very few manufacturers make true see-through inserts designed to slide into an existing two-sided masonry opening, because the openings vary widely in size and the unit must be serviceable from both rooms.

In practice, homeowners who want to upgrade a see-through fireplace usually end up with one of four solutions:

1. A see-through gas insert sized for the existing masonry opening, where a model exists that fits.
2. A zero-clearance see-through fireplace (gas or wood) that replaces the old firebox entirely after the masonry is partly removed and reframed.
3. A double-sided electric insert or firebox that needs no venting at all.
4. Closing off one side with a noncombustible panel and installing a standard single-sided insert facing the room where you want the heat.

Understanding which path fits your house is the first step, and a fireplace specialist can confirm it after measuring and inspecting the existing firebox and chimney.

Gas See-Through Inserts and Fireplaces

Direct-vent gas is the most popular choice for two-sided installations. The firebox is sealed behind fixed glass on both sides, and a coaxial or co-linear vent pulls combustion air from outside and exhausts combustion gases outside. Because no room air is used, drafts between rooms stop and efficiency climbs dramatically compared with an open masonry fireplace.

• Heat output: typically 20,000 to 40,000 BTU per hour, enough to supplement heat in two connected rooms.
• Viewing size: common widths are 36, 42, and 48 inches, with some linear models reaching 60 inches or more.
• Venting: through an existing chimney using two flexible aluminum liners (co-linear), or through a new coaxial pipe out a wall or roof when the unit is a zero-clearance replacement.
• Controls: remote and wall-switch operation, variable flame height, and optional blowers.

Since 2015, gas fireplaces and inserts sold in the U.S. have been required under ANSI Z21.88 to ship with a safety barrier screen over the glass. See-through glass can exceed 500°F in operation, and a see-through unit has two hot faces, so these screens need to stay in place on both sides, especially in homes with small children or pets.

Ventless Gas Options

Vent-free two-sided gas units exist, but they release combustion byproducts and moisture into the house. Several states and many local jurisdictions restrict or prohibit them, and they are generally not permitted in bedrooms or bathrooms. For a see-through fireplace that connects to a bedroom, direct-vent is the safer and more widely accepted choice.

Wood-Burning See-Through Options

If you want a real wood fire visible from both rooms, the usual approach is a factory-built, EPA-certified see-through wood fireplace rather than an insert. These units have tightly fitting doors on both sides, and one door is typically used for loading. They require a listed Class A chimney sized to the unit, usually 8 to 10 inches in diameter.

Two-sided wood units tend to be less efficient than single-sided wood inserts, and both doors must seal well to prevent smoke spillage when one door is opened. Expect to pay $4,000 to $8,000 for the unit alone and $8,000 to $18,000 installed, including chimney work. Wood-burning also carries ongoing chores: seasoned wood below 20 percent moisture, annual chimney sweeping, and ash removal from inside a firebox that opens into two rooms.

Double-Sided Electric Inserts

Electric see-through fireboxes are the easiest option by far. They produce a realistic LED flame visible from both sides, need no chimney or gas line, and typically include a fan-forced heater of about 5,000 BTU (1,500 watts). Many run on a standard 120-volt circuit, while larger units may need a dedicated 240-volt line.

• Unit cost: $1,200 to $4,000 for 36- to 60-inch two-sided models.
• Installation: $300 to $1,500 for framing, a dedicated circuit, and finish work.
• Heat: enough to take the chill off a room, not to heat a home.

Electric is a strong fit if you mainly want the look, if your chimney is in poor condition, or if you are adding a see-through feature in a wall that never had a fireplace. It can also be installed in an existing masonry opening, but block the chimney with a sealed damper or insulated plug to stop drafts and heat loss.

Double Sided Fireplace Insert Costs

Costs vary with fuel type, whether the old firebox must be removed, and how much finish work each side needs. Remember that a see-through installation means two faces of stone, tile, or trim, so finish costs are roughly double those of a single-sided fireplace.

Other line items to anticipate include a gas line extension ($250 to $1,000), chimney liner installation ($1,500 to $3,500), masonry demolition and reframing ($1,000 to $4,000), and permits ($100 to $400).

Installation Steps and What to Expect

For a gas see-through conversion, a typical project follows this sequence:

1. Chimney inspection: NFPA 211 calls for a Level II inspection whenever you change the appliance type connected to a chimney. Expect $200 to $500 with a video scan of the flue.
2. Measurement and model selection: the installer measures both openings, the depth, and the flue to confirm a unit fits or whether a zero-clearance replacement is required.
3. Demolition and framing: if the old firebox must go, masonry is removed and a noncombustible or listed framed enclosure is built to the new unit’s clearances.
4. Gas and venting: a licensed plumber or gas fitter runs the supply line, and the installer sets the vent liners or new direct-vent pipe with the correct termination cap.
5. Setting the unit and finishing: the unit is leveled, connected, and tested, then each face receives its surround and mantel within the manufacturer’s clearance to combustibles.

Most gas conversions take two to five days of work, spread over one to three weeks when permits, inspections, and stone or tile finish work are involved.

Fixing Smoke and Draft Problems in Existing See-Through Fireplaces

Many homeowners start shopping for an insert because their open see-through fireplace smokes into one room. The cause is usually physics. A two-sided opening has roughly twice the face area of a standard fireplace, and the chimney flue often is not large enough to pull that much air. A common rule of thumb is that the flue area should be at least one-tenth of the total opening area for an open fireplace, and many see-through fireplaces fall short. Cross-drafts from a door or HVAC register on one side can also push smoke out the other.

A sealed insert or direct-vent unit solves this completely because it no longer draws room air through the openings. If you want to keep an open wood fire, a chimney professional may suggest reducing the opening height with a metal smoke guard, extending the chimney, adding a top-mounted damper, or installing glass doors on both sides. These fixes cost far less than a full conversion, so it is worth diagnosing the problem before committing to a new unit.

Safety, Codes, and When to Call a Licensed Professional

A see-through fireplace combines gas or solid fuel, venting, and structural changes in the wall between two rooms, so this is not a DIY project for most homeowners. Hire a licensed professional in these situations:

• Any gas line work, which in nearly every jurisdiction requires a licensed gas fitter or plumber and a permit.
• Chimney relining, venting changes, or a new wall or roof termination.
• Removing masonry, which may involve load-bearing elements or a hearth supported by the floor framing.
• Any wood-burning installation, which should be done by an NFI-certified specialist.

Mantels, trim, and combustible finishes must stay outside the clearances listed in the installation manual, and those clearances apply to both faces. Install a carbon monoxide alarm in each room the fireplace opens into and smoke alarms on every level. Have gas units serviced every year to check the burner, pilot, glass gasket, and vent connections; a cracked gasket or loose vent joint can let exhaust into the house.

Choosing the Right Double-Sided Solution

If you love the look and want real heat with minimal upkeep, a direct-vent gas see-through unit is the best all-around choice. If a crackling wood fire is non-negotiable, plan for a certified see-through wood fireplace and a new chimney system. If you want the ambiance on a smaller budget, or your chimney is not worth saving, a double-sided electric firebox delivers the view with none of the venting. And if you mostly sit on one side, closing the rear opening and installing an efficient single-sided insert may deliver the most heat for the money.

Start with a chimney inspection and a site visit from a hearth specialist, get written quotes that include finish work on both sides, and confirm permit requirements with your local building department. With the right double sided fireplace insert or replacement unit, a drafty, smoky see-through fireplace can become the warmest and most-used feature in your home.