How to Install a Gas Fireplace

Silver fireplace inset into a black and white wall


  • Total Time: 2 - 5 days
  • Skill Level: Advanced
  • Estimated Cost: $2,000 to $3,000

With prices for natural gas holding fairly low for quite some time, a gas fireplace is a popular approach to adding warmth and ambiance to your home. Good gas fireplaces are considerably more efficient than wood-burning fireplaces, which generally drain more heat from drafts going up the chimney than they produce. A good airtight gas-burning fireplace with a circulating blower, on the other hand, is nearly as efficient as a furnace for adding heat to a room. And when equipped with good gas burners and realistic ceramic logs, gas fireplaces are extremely attractive and practical.

Installing a gas fireplace yourself, however, is most definitely an advanced DIY project, and you shouldn't attempt it before thoroughly researching the work required and the installation instructions for any fireplace units you are considering.

Gas Fireplace Variations

Gas fireplaces come in several styles for different applications. For example, if you have an existing wood-burning fireplace, the firebox can be fitted with a gas-burning insert to convert it to a gas fireplace. This will require a considerable amount of renovation work, however, including running new gas lines and installing a different type of chimney flue. You can't simply vent a gas-burning fireplace up the existing masonry flue of a wood-burning fireplace. For this reason, retrofitting a gas fireplace into a wood-burning masonry fireplace is almost always done by a company specializing in this work.

If you are installing a brand-new gas fireplace where none existed—for example, in a newly finished family room, room addition, or in a basement or attic finishing project—there are two types to choose from: direct-venting units and non-venting units.

Direct-venting fireplaces are the standard type and the best choice for most applications. These fireplaces have a metal flue or chimney that vents combustion fumes directly to the outdoors, either through the sidewall of the home or up through a metal chimney through the roof. These metal flues are specially double-wall designs made expressly for this kind of application. You can't use ordinary metal ductwork to vent a gas fireplace, as the heat generated is more than ordinary ductwork can handle.

There are also vent-free fireplaces that use special burners designed to burn very efficiently, producing such a small amount of combustion gas that they can vent back directly into the room rather than to the outdoors. While these might seem like a great option that allows you to bypass the complicated work of running vent pipes, the use of vent-free fireplaces is controversial, and in some places, it is outlawed due to safety concerns. Several states prohibit the use of vent-free fireplaces, and in other locales, they may be forbidden in bedrooms.

The installation example described here will feature a traditional direct-vent fireplace that exhausts to the outdoors.

DIY Installation

For most people, hiring professionals is the preferred strategy for adding a gas fireplace to the home. This process involves several skills that are somewhat complicated, and local laws may even forbid you from doing some aspects of the project. While a moderately experienced DIYer can do the carpentry work required to frame in the box to hold the fireplace and finish the surround treatment and trim, it generally takes a licensed professional to run the gas piping to the fireplace unit.

In addition, installing a modern gas fireplace usually involves running a new electrical circuit, or extending an existing circuit, to provide power to the blower and timer features on the fireplace. In some states, this is work that can only be done by a licensed electrician.

Finally, fireplace installation requires running special vent flues out the sidewall or through the roof of your home. This can be tricky work that is often best handled by a pro.

Despite these complications, many homeowners can and do install gas fireplaces themselves. But if you take on this project, make sure that you follow local regulations for obtaining building permits and following inspection schedules. One option may be to perform the carpentry framing and finishing work yourself but hire a plumber and electrician to do the critical work of running gas and electrical lines.

Gas fireplaces usually come with detailed instructions for installation. Make sure to follow these directions precisely to ensure a safe installation. The quantities of materials such as framing lumber, finish trim, and metal flues will vary widely depending on the unit you buy and the configuration of your installation. Your own project could vary considerably from the overview described here. Careful planning is essential to a smooth installation.

What You'll Need

Equipment / Tools

  • Tape measure
  • Utility knife
  • Power miter saw or circular saw
  • Screwgun
  • Hammer or power nailer
  • Drill
  • Caulk gun
  • Pencil
  • Drywall saw
  • Reciprocating saw (optional)
  • Aviation shears
  • Drywall knives
  • Tile cutter or tile saw
  • Thinset adhesive trowel
  • Grout float
  • Grout sponge


  • Cardboard boxes (optional)
  • 2x10 and 2x4 framing lumber, as needed
  • 3/4-inch plywood, as needed
  • Utility screws or framing nails
  • Gas fireplace unit
  • High-temperature silicone caulk
  • Metal vent components, as needed
  • Sheet metal screws (as needed)
  • Vent cap with fire-stop plates
  • 1/2-inch drywall panels, as needed
  • Metal corner bead
  • Drywall taping compound
  • Cement backer board
  • Ceramic tile for surround area
  • Thinset tile adhesive
  • Tile grout
  • Grout sealer
  • Trim lumber (as needed)
  • Finish nails/brads


This demonstration project describes a fairly simple gas fireplace installation, in which the fireplace unit rests inside a box frame constructed from ordinary framing lumber. Gas and electrical lines are extended to the frame, and the venting flue is run directly through the sidewall of the house. Once the fireplace is installed, the frame walls are finished with ordinary drywall panels, with ceramic tile used for the surround area immediately around the fireplace. The fireplace is then trimmed out with wood moldings to give it a finished look.

  1. Plan the Location

    There are many ways you can configure a gas fireplace installation and many different fireplace models to choose from, so careful planning is essential. For example, it is possible to build a fireplace that is inset into the exterior wall so most of the unit juts outside while leaving the interior footprint of the room intact. But this approach does require a considerable amount of exterior carpentry to box in the portion fireplace box that extends outdoors.

    Or, you can create a fireplace that sits within a frame constructed along an interior wall of the room. This method will not interfere with the outdoor facade of the home, but it can take up a considerable amount of interior space in the room. There are even corner fireplace units designed to fit within a frame built into the corner of the room.

    One approach to planning is to construct a mock-up of the fireplace from cardboard, then position it at various places in the room to determine where it will best fit. When you decide the best location for the fireplace, then you can buy the fireplace unit and thoroughly study the instruction specifications.

  2. Build the Pedestal

    Most fireplaces must be supported well above the floor to ensure that heat from the fireplace can't damage floor framing, so a fireplace installation typically begins by building a pedestal base from 2x10 lumber and 3/4-inch plywood. This pedestal should be sized according to the fireplace instructions. The pieces of the pedestal can be joined together with framing nails or utility screws. Secure the pedestal to the floor following the wall-distance clearances specified by the instructions.

  3. Position the Fireplace

    Move the fireplace into position on the pedestal. The fireplace unit is quite heavy, so this work will be best accomplished with at least one helper assisting you. Apply a thin bead of high-temp silicone caulk around the flue collar on the top of the firebox, then slide the first vent pipe segment over the flue collar. Your fireplace may require a gasket forced into the joint between the vent and the fireplace; if so, press it in place at this time.

    Lock the first vent pipe segment in place according to the manufacturer's directions. This may require driving sheet metal screws to hold the pieces together.

  4. Open the Wall

    Most gas fireplaces are vented out the back wall behind the fireplace, using an L-shaped vent that extends upward from the firebox a foot or so, then makes a sharp 90-degree bend that penetrates through the back wall and terminates in a vent cap with a firestop. This is a little more complicated than just punching through the wall and extending the vent pipe, as the opening must be carefully framed and the vent pipe must be collared on both the inside and outside surfaces with fire-stop plates that prevent excessive heat from radiating to the walls.

    Begin by marking the interior wall where the vent pipe will extend through. This is easiest to do by loosely assembling the vent pipe pieces and elbow, then tracing around the vent pipe to show where it will extend through the wall. Next, position the interior fire-stop plate over the marked outline, and trace around the square fire-stop plate. Use a wallboard saw to cut along the fire-stop outline and remove the drywall, leaving a square opening into the wall cavity.

    You will now need to create a square frame in the wall cavity to secure the vent pipe and fire-stop plates, using 2x4 lumber. If your vent opening happens to lie over an existing wall stud, this may mean that you'll need to remove a section of the stud in order to create the frame for the vent pipe.

    Now, you need to remove the outer siding to fully open up the wall. This is easiest to do by drilling a series of pilot holes through from the inside, around the edges of the vent frame. Then, from the outside, cut away the siding along the pilot holes and remove the siding and sheathing. You now have a square opening through the exterior wall, which will hold the round vent pipe and square fire-stop collars.

  5. Complete the Vent Pipe

    With the exterior wall open, you can now assemble the vent pipe sections using sheet metal screws. Depending on the required length, you may need to cut the vent pipe to size using aviation shears.

    The L-shaped vent pipe is held within the wall frame with metal fire-stop collars that keep the pipe from touching the wood framing members. The collars are screwed to the vent frame—one on the outside and one on the inside—then the vent pipe is extended through the collars.

    Seal the gaps between the vent pipe and the fire-stop collars with high-temperature silicone caulk, then attach the outer cap as directed by the manufacturer.

  6. Run Gas Lines

    Before beginning work on the frame around the fireplace, have a plumber or heating specialist run gas lines for the fireplace. In most cases, the plumber will extend existing natural gas or propane lines already running to the furnace or another gas appliance. The plumber should also install a shutoff valve to allow for easy shutoff of gas in case of an emergency. This shutoff valve needs to remain accessible; it can't be walled over inside the fireplace frame.

    Because the walls behind the fireplace will be hidden by a frame around the fireplace, it is fine for the plumber to open up walls in order to run the gas line. There is no need to patch walls if the plumber or electrician opens these wall cavities since they will be hidden by the fireplace frame.

  7. Run Electrical Service

    If your fireplace has an air circulating fan or electric controls (most do), have an electrician run a new circuit or extend an existing circuit to provide the necessary power to the fireplace unit. If your fireplace frame will cover up an existing outlet, the electrician should also remove and reroute these electrical cables, as it is illegal to cover up existing outlets.

  8. Build the Frame

    Based on the fireplace instructions, use 2x4 construction lumber to build a frame to box around the fireplace. Most fireplaces have very specific instructions for the height above the floor and clearances between the edges of the firebox and adjoining frame walls. These clearances are critical for safety, so make sure to follow the instructions closely when building the frame surround the fireplace. The frame MUST be large enough to provide the necessary clearances around the firebox.

    There are many ways to construct the fireplace frame. If the vent flue will be routed out the back wall, then you can terminate the frame two feet or so above the horizontal flue, creating a flat top to serve as a mantel above the fireplace unit. If the vent flue will extend straight up through the roof, then most installers will build the fireplace frame to create full walls from floor to ceiling. The frame provides a "chase" to run the vent flue all the way up through the attic and through the room.

    Use standard construction methods to build the frame, spacing the frame studs 16 inches apart.

    Note: Make sure your frame allows for access to any shutoff valves or wire-connection panels in the fireplace. This may entail adding a removable hatch or door.

  9. Finish the Frame Walls

    The vertical walls of the fireplace frame can now be finished with standard 1/2-inch drywall panels. If you will be using ceramic tile to cover the surround area around the fireplace, use cement backer board to cover the frame studs in this area.

    If the fireplace frame will end below the ceiling, use 3/4-inch plywood to cover the top of the frame. This will create a sturdy horizontal mantel above the framed-in fireplace.

    Once the drywall and backer board is installed, use metal corner bead to cover any corners, then tape and mud the seams and corners, following standard drywalling techniques.

  10. Finish Fireplace Surround (Optional)

    Next, apply ceramic tile over the surround area around the fireplace if your design includes this. This works uses the same tile-setting techniques used for any wall tile installation, and will require trowels, a tile cutter or wet saw, thin-set adhesive, grout and grout sponge, and grout sealer. A ceramic tile surround is an opportunity to get creative with your fireplace project, so spend some time designing the pattern you want.

    Make sure the tile has fully set up and the grout is fully hardened and sealed before you use the fireplace.

  11. Complete the Trim

    Finish the installation by attaching whatever wood trim you choose. This can range from a simple wood edge molding to frame around the fireplace to an elaborate faux paneling treatment or extended "pillars" that give the fireplace a truly classic built-in look. If you wish, you can also buy and install a mantelpiece.

    A power miter saw and power nailer are the best tools for cutting and attaching these trim pieces.