Adding or converting a fireplace during a remodel is a scope that varies more in cost and complexity than most homeowners expect. The range from a prefabricated gas insert in an existing masonry firebox to a built-in gas fireplace in a new framed chase is significant — in both cost and the construction work required. Understanding what each option actually involves prevents scope surprises mid-project.
Here's what fireplace work in a remodel actually requires, and what drives cost and timeline.
Gas Fireplace Insert vs. Built-In: The Core Decision
The starting point for any fireplace scope is whether you're working with an existing firebox or starting from scratch:
- Gas insert in existing masonry: the least invasive approach. A gas insert fits into an existing masonry fireplace opening, vents through the existing chimney (with a liner), and provides a gas fire with a realistic appearance. Cost range: $3,000–$6,500 installed, including liner. No structural work required if the firebox and chimney are in good condition.
- Direct-vent built-in gas fireplace: a new gas fireplace unit installed in a framed chase, venting directly through an exterior wall or roof. This approach allows placement anywhere in the house, not just where a masonry chimney exists. Cost range: $6,000–$15,000 installed depending on unit, surround, and vent run complexity.
- B-vent (natural draft): a venting method that uses room air for combustion and vents through a flue to exterior. B-vent requires a vertical flue run and cannot go through a wall horizontally. Less common in new installations today; primarily encountered in existing systems.
- Linear gas fireplace: contemporary design option — a wide, low-profile firebox that fits in a recessed wall installation. These units require specific clearance, structural support, and a vent run that's designed to the unit. Cost: $7,000–$20,000 installed, with the range driven by unit cost and surround complexity.
Framing, Clearances, and Finish Surround Options
The construction work around a new fireplace is often more involved than the fireplace itself:
- Framing clearances: all gas fireplace units have minimum clearances to combustibles — typically 1–2 inches on sides and top. Framing must be built to accommodate the unit and its clearances, then finished with non-combustible materials (tile, stone, steel) within the clearance zone.
- Hearth extension code: a gas fireplace with a screen or door does not require a hearth extension under most codes. An open-face gas fireplace (no screen) requires a hearth extension of at least 16 inches in front and 8 inches on each side, of non-combustible material.
- Mantel clearances: combustible mantels have minimum distance requirements above the fireplace opening — typically 12 inches above the opening for every inch of projection beyond 1.5 inches. This determines how high the mantel can be placed above the unit.
- Finish surround options: tile (most common, widest design range), stone (natural or manufactured, higher cost), steel plate (contemporary applications, requires metalwork fabrication), and prefabricated surrounds (manufacturer-supplied, faster installation but limited design flexibility).
- Electrical requirement: most built-in gas fireplaces require a 120V outlet within the chase for the ignition, blower, and controls. This must be roughed in before framing is closed.
KCC designs and installs gas fireplaces as part of whole-home and addition projects throughout the West Metro. If you're considering a fireplace addition or conversion in Edina, Minnetonka, or Plymouth, request a consultation to discuss the options and what the scope actually involves.