How to Install a Gas Fireplace

Updated: Feb. 22, 2023

Complete DIY instructions for installing a direct-vent gas fireplace

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Enjoy the comfort and ambiance of a crackling fire on a cold winter's night. Here we'll show you how to install a gas fireplace. Don't worry about installing a chimney. You don't need one. You simply vent the fireplace out the side of the house. Once the fireplace is installed, you just flip a switch to start a roaring fire.

Tools Required

  • Brad nail gun
  • Caulk gun
  • Circular saw
  • Cordless drill
  • Drill bit set
  • Drywall sander
  • Drywall saw
  • Dust mask
  • Hammer
  • Hearing protection
  • Knee pads
  • Knockdown knife
  • Level
  • Mud pan
  • Paintbrush
  • Rasp
  • Roller sleeve
  • Roller tray
  • Sanding block
  • Sanding pole
  • Screw gun
  • Socket/ratchet set
  • Straightedge
  • Stud finder
  • T-square
  • Tape measure
  • Tin snips
  • Utility knife

Materials Required

  • 1/2x48x96 drywall
  • 100-grit sandpaper
  • 2x10x12' lumber (2)
  • 3/4x4x4' plywood
  • 9" vent pipe
  • Acrylic caulk
  • Corner beads
  • Gas fireplace
  • Heat shield flashing
  • Interior firestop
  • Joint compound
  • Metal drip cap
  • Metal nail plates
  • Paint or textured finished
  • Polyurethane caulk
  • Silicone caulk
  • Straight pipe

Choosing a Gas Fireplace

It’s hard to beat a crackling wood fire on a chilly night. But modern gas fireplace come pretty close, and without the drawbacks of wood. Not only does gas burn much cleaner, making it a better choice for the environment, but there are no messy logs to carry through the house or ashes to clean out. And lighting the fire is as simple as flicking a switch or turning a valve.

A direct-vent gas fireplace doesn’t need a chimney. Rather, you can run a special vent to the outside through an exterior wall. This process is simple and fire-safe as long as you follow the manufacturer’s directions. Be sure to read them carefully, because they might differ slightly from what we show here. For fire safety, however, make sure to heed the manufacturer’s directions on clearances for combustibles.

Cost to Install a Gas Fireplace

Wondering how much does it cost to install a gas fireplace? If you have some carpentry and drywalling experience, you shouldn’t have any trouble finishing this project. The fireplace will take you about a day to install. Then plan to spend an entire weekend framing and installing drywall and a few hours each day for the rest of the week troweling on additional coats of joint compound. The following weekend you can prime the walls and apply the texture.

  • The direct-vent fireplace and vent parts we purchased cost us about $1,800. For $650 more, our fireplace dealer would have installed the fireplace, not including the gas and electric hookups or any interior finishing.
  • The materials for the wood framing, drywall and stucco coating cost an additional $175. Hire a plumber to run the gas line during the framing process and connect it to the fireplace ($250 to $500).

In addition to a basic set of hand tools, you’ll need a circular saw and a drill. A power miter box is handy but not necessary for cutting the angles on the framing parts. You’ll need a tin snips for cutting the metal corner bead, a collection of taping knives (2-in., 4-in., 6-in. and 12-in.) and a mud pan for applying the joint compound and texture.

Shopping for a Gas Fireplace

The fireplace we’re using, and the type we recommend, is a direct-vent fireplace. This type draws air from outdoors to feed the flame. Not only is this setup more efficient because you’re not losing valuable heated air up the chimney, it’s safer too because it greatly reduces the possibility of dangerous carbon monoxide backing up into your home.

The best place to shop for fireplaces is at fireplace dealers that have showrooms with working models on display. You’ll be able to see how the artificial logs look when they’re burning and pick a fireplace style you like.

Make Sure You Have Proper Venting

Adding a fireplace to a house is a complex project, but you can do it yourself. Proper ventilation is essential for a safe-operating fireplace.

Project step-by-step (22)

Step 1

Build a Mockup To Find the Best Position

Mock up the fireplace using the dimensions given in fireplace brochures and outline the hearth shape with masking tape. Your new fireplace will have a major impact on your room. Build a simple mock-up to get a feel for the amount of space it takes up and to see how the angled placement will affect furniture arrangement and traffic patterns.

When you’re satisfied with the aesthetics of the fireplace, turn your attention to the mechanical requirements. You’ll need to run a gas supply line for the fireplace. Call in a plumber to plan the route before you order the fireplace.

Most gas fireplaces don’t require electricity to operate. However, if you ever decide to add a blower to increase heat output or a hand-held remote control, you’ll have to connect the fireplace to an available electrical circuit, so run a wire to the fireplace while it’s accessible.

In addition, since electrical codes don’t allow you to simply cover a box that contains live wires, you’ll have to disconnect or relocate any boxes or receptacles that will be covered by the new fireplace.

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Step 2

Get the Gas, Electrical and Vent in Place First

Determine how you’ll get the vent from the fireplace to the outdoors. Thanks to the ingenious two-layer design that keeps the outside of the pipe relatively cool, the vents from direct-vent fireplaces can run straight out through the wall or up through the roof, allowing great flexibility in design and placement of the fireplace. Even so, there are very specific requirements that your fireplace and vent installation must meet. Check the installation manual to make sure. Here are a few key points to look for:

  • Clearances from the fireplace box to surrounding walls and to the wood framing. Ours required 1/2 in. on the sides and back and 3-1/2 in. on top.
  • Distance the vent must be kept from insulation, wood and other combustibles. Sometimes metal shields must be used over the top of the vent to divert the heat.
  • Maximum number of bends in the vent pipes and the relationship of horizontal to vertical lengths of pipes. Our manual had many illustrations with dimensions to help with the venting layout. You can ask the dealer for help with vent design.
  • Distance the vent cap must be kept from windows, doors, corners and other elements at the point where it leaves the house. Measure where the vent pipe will come out and make sure it meets the specifications.
  • And before you begin, contact the local building inspections department to obtain the permits required for a fireplace installation.

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Step 3

Build a Fireplace Platform

  • Cut 2x10s and nail them together to create an 11-1/2 in. tall platform the shape of the fireplace.
  • Nail 2×4 cleats to the bottom.
  • Cut 3/4-in. plywood to fit and screw it to the top.

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Step 4

Set the Fireplace in Position

  • Set the fireplace on the platform and slide it into position.
  • Then apply a pencil-width bead of sealant to the starting collar of the fireplace.
  • Use the sealant recommended by the manufacturer, usually stove cement or high-temperature silicone caulk.

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Step 5

Install the First Vent Pipe

  • Slide the first vent pipe over the starting collar and lock it in place according to the instructions.
  • If your fireplace requires a gasket to seal the joint between the vent and fireplace, make sure it’s properly positioned. (Ours required the braided rope gasket shown.)

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Step 6

Finish the Vent Pipe

  • Connect the 90-degree elbow and a 9-in. straight section to the first vent pipe. They should meet the exterior wall at a 90-degree angle.
  • Trace a circle around the pipe on the wall.
  • Using the interior firestop for reference, mark a 12-in. square on the wall. Our square is centered 1 in. above the center of the vent pipe.

With the preliminaries out of the way, here’s how you proceed.

  • First order the fireplace and vent parts.
  • When you know the delivery date, schedule the plumber and electrician to show up a few days later. This will give you time to accurately lay out the fireplace location on the floor, build the platform and run the vent.
  • After the gas line and wiring are done and all inspections are completed, you’ll build the frame, cover it with drywall, and complete the taping and decorating.

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Step 7

Punching Through the Wall Is the Tough Part

  • Cut out the 12-in. square hole with a drywall saw and look for obstructions.
  • If there’s a wall stud in the way, cut out the drywall between the two closest studs and about 9 in. above the square opening.

Caution: Keep the saw blade shallow to avoid cutting hidden electrical wires.

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Step 8

Frame the Opening

  • Cut out the wall stud and add a double 2×6 header.
  • Support the header with trimmers screwed to the existing studs.
  • Notch for electrical cables if necessary. (A metal nail plate is required if the cable is closer than 1-1/4 in. to the face of the framing.)
  • Frame the 12-in. opening.
  • Drill a 3/8-in. hole through the wall at each corner to transfer the location of the opening to the outside.

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Step 9

Remove the Siding

  • Connect the four holes with lines and cut out the 12-in. opening in the siding and sheathing.
  • Mark another square opening the size of your exterior firestop and cap, and cut through the siding only.
  • Finish the corners with a utility knife or chisel. Vinyl, aluminum, stucco and brick siding require different techniques.

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Step 10

Install the Interior Firestop

  • Replace the insulation and drywall, reusing the old piece if possible.
  • Seal the drywall seams with caulk and place a bead of caulk around the opening.
  • Press the interior firestop into the caulk and screw it to the wall.

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Step 11

Caulk the Firestop

  • Complete the vent by sliding a section of pipe through the firestop from the outside.
  • In our case this pipe was part of the telescoping exterior firestop and cap.
  • Then seal the gap between the vent and the interior firestop with high-temperature silicone caulk.

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Step 12

Install the Vent

  • Slide the combination firestop and vent termination into the telescoping section.
  • Screw the firestop to the wall and seal it with caulk.
  • If your cap has a built-in drip cap that prevents you from sliding it in, cut it off and slide a pre-bent drip cap under the siding as shown.

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Step 13

Run Electric and Gas Lines

  • Fine-tune the position and levelness of the fireplace and screw the platform to the floor.
  • Relocate electrical boxes as needed and run a new electrical line if you intend to install the optional fan or remote control.
  • Run the new gas line.
  • Screw wood backing between the studs to secure the surround as needed.

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Step 14

Build the Wall Surrounds

  • Build the wall that surrounds the fireplace using Fig. A as a guide.
  • Allow 1/2 in. of space between the wood framing and the fireplace on both sides.
  • Screw the metal tabs on the fireplace to the wood frame to secure it.

Note: You can download and print Figure A from the Additional Information section below.

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Step 15

Build the Mantel

  • Preassemble the mantel frame and slide it into position.
  • Screw through the 2×6 from the backside to secure the mantel.

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Step 16

Finish Assembling the Mantel

  • Miter short framing members to complete the angled ends of the mantel and attach them with screws.

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Step 17

Build the Hearth

  • Construct the hearth of 2x10s covered with two layers of 3/4-in. plywood.
  • Cut the plywood to shape first and use it as a pattern to build the 2×10 frame.
  • Support the inside edge with 2x4s screwed to the framing.

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Step 18

Build the Columns

  • Build the columns according to Fig. A and screw them to the framing.
  • Then cover all wood surfaces with drywall fastened with 1-1/4 in. drywall screws.
  • If your fireplace is a different size from ours, you’ll have to adjust the wood framing dimensions.

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Step 19

Nail on the Corner Bead

  • Cover all the outside corners with metal drywall corner bead. Where two or more corner beads meet, cut angles on the ends to form a point.
  • Nail the beads with 1-1/4 in. ring-shank drywall nails every 12 in. along the bead or more often if needed.
  • Use special 120-degree metal bead to cover the angles that are greater than 90 degrees.

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Step 20

Tape the Joints

  • Apply paper tape embedded in a layer of drywall joint compound to joints without corner bead.
  • Fill the area between corner beads with joint compound.
  • Sand the corners and joints smooth with 100-grit drywall sanding paper.
  • Because of shrinkage, the taping and filling process requires at least three coats, with drying time in between, so be sure to allow a few days to finish.

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Step 21

Premixed Texture Make You Feel Like a Master Plasterer

We decided to apply a sandy, plaster-like finish to the drywall on our fireplace. There are a dozen ways to accomplish this look. We chose an acrylic-based product manufactured by USG that’s typically used as an exterior finish. The USG Exterior Textured Finish is available in five textures, from fine to coarse, and 25 standard colors.

Troweling on the texture is a messy operation, so mask off the walls and floor and put on some old clothes before you start. First prime the walls with a top-quality drywall primer. When the primer is dry, use a wide trowel to spread a thin layer of the premixed texture over an entire section, stopping at a breaking point like a corner.

  • Prime the walls, then trowel on a layer of premixed acrylic stucco texture.
  • Press the trowel firmly against the wall. Cover all of one section.

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Step 22

Give the Stucco Texture

Next you’ll float the area to impart texture and smooth out the trowel marks. If you’re working in hot, dry conditions, start floating immediately. Otherwise you may have to let the texture mix set up for a few minutes.

You’ll have to experiment a little to see what works. We used a square of extruded polystyrene foam insulation to float the texture, but a grout float, wooden block or hard plastic trowel also will work. Each tool gives a little different texture. Practice on a large scrap of drywall to get a feel for the material and refine your floating technique. Work from the top down to avoid splattering on completed texture.

  • Rub block of foam insulation in small sweeping arcs over the compound to impart a stucco-like texture.
  • Occasionally clean off texture that builds up on the block.
  • Cut a 45-degree angle on a block to reach into inside corners.
  • Clean up spills and splatters with water before they dry and occasionally clean your tools and float in a bucket of water to avoid a buildup of dry texture mix. Then move on to the next section.
  • If you do mess up a section, it’s no big deal—just scrape it all off before it dries and start over with fresh texture mix.
  • When the texture is dry, usually overnight, you can assemble the log set and light the fireplace. Follow the manufacturer’s instructions for the exact procedure.
  • If necessary, ask the plumber to help you light the pilot and fire up the burner.
  • The smell of burning oil will go away once the factory residue burns off.

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