How to Install a Gas Fireplace Insert and When to Call a Pro

How Do You Measure Your Fireplace for an Insert?

A gas insert must fit snugly inside your existing firebox (the inner cavity where fires burn). If the chassis is even half an inch too tall or deep, the metal frame will stick out past the hearth. Taking six measurements prevents ordering errors and confirms your hearth meets safety clearances.

Grab a tape measure, a notepad, and a flashlight. Record each dimension to the nearest eighth of an inch:

• Front opening width: Measure across the front opening from left to right at both the top and bottom. Record the smaller number.
• Rear opening width: Most wood fireplaces taper inward toward the back. Measure across the rear brick face, which is often the tightest pinch point.
• Opening height: Measure vertically from the firebox floor to the lowest point of the opening or steel lintel bar.
• Firebox depth: Measure from the front face of the masonry straight back to the rear wall along the floor and near the top.
• Hearth extension: Measure how far your non-combustible floor extends into the room, along with its thickness.
• Clearances to combustibles: Measure the distance from the opening top to your wood mantel, and from the sides to any nearby trim or walls.

Manufacturer manuals specify minimum clearances to mantels and side walls. If your mantel sits closer than listed, you will need a metal deflector hood or a shallower insert.

How Do Vent Pipes Fit Down Your Chimney?

Most modern gas inserts use a direct-vent system. Direct vent means a sealed two-pipe system that draws outside air to feed the flames and vents exhaust safely back outside. Unlike an open wood fire, a direct-vent insert never pulls heated room air up the chimney or pushes drafts into your living room.

These systems require two flue liners (flexible metal vent pipes inside the chimney). One pipe measures three inches across for combustion air, while the other measures three or four inches across for exhaust. Both flexible aluminum or stainless steel pipes run the entire height of your chimney from the roof cap down to the firebox.

Before installing pipes, address your old chimney damper. The damper is the movable metal plate inside the throat of the chimney that closes off drafts. Because the flexible pipes must pass straight through this throat, you must remove the damper plate or lock it open permanently with a steel clamp. For more on how chimney throats operate, see our guide on how to handle a fireplace damper.

Dropping the liners requires two people. One person stands on the roof uncoiling the pipe, while a helper guides the bottom end from inside the hearth. Attaching a rope and rounded pull cone helps guide the flexible pipe past rough masonry ledges without ripping the metal.

At the roof, the liners attach to a chimney termination cap. This metal cap seals the top flue opening with a flashing plate and silicone sealant. It keeps the intake and exhaust separated and stops rain, debris, and animals from entering the chimney.

How Do You Run Gas and Power Lines Safely?

A gas insert needs two utilities: fuel to produce heat and electricity to run the blower fan and controls. Planning these connections before sliding the heavy chassis into place prevents costly mistakes.

For fuel, your installer routes a dedicated gas line into the firebox cavity. In a brick hearth, this involves drilling through the side or rear masonry with a rotary hammer drill. The line supplies either natural gas or propane, matching your unit. Building codes require a manual shut-off valve located near the hearth or behind the lower control panel so you can cut fuel quickly during servicing.

Electricity powers the internal blower fan (the heating vent or blower grille that pushes warm air into your room). It also powers electronic spark ignitions and remote control receivers. The cleanest approach is having an electrician install a standard 120-volt wall outlet inside the lower back corner of the firebox.

Never run an extension cord through masonry walls or beneath the hearth trim. Extension cords can pinch, overheat, or melt against hot sheet metal, creating an immediate fire hazard.

Working with fuel lines and wiring presents serious safety hazards. A loose gas joint can leak vapor into your walls, and faulty wiring creates shock risks. While homeowners can handle measuring and cleaning, hiring a licensed plumber and electrician for the utility connections ensures your system complies with local fire safety codes.

What Are the Steps to Slide In the Insert?

Once your chimney liners, gas line, and electrical outlet are ready, you can position the insert chassis into the opening. Follow these steps in order to avoid scratching surfaces or pinching lines:

1. Clean the firebox floor: Sweep away loose soot, mortar chips, and wood ash with a vacuum. Grit left behind will scratch your hearth tiles and prevent the metal base from sitting flat.
2. Protect your hearth surface: Lay a thick moving blanket or heavy cardboard across the hearth. The metal insert chassis often weighs over one hundred pounds, and sharp steel edges can chip slate or scratch wood flooring.
3. Position the vent collar plate: Many inserts feature a detachable exhaust slide plate on top. Connect your two flexible flue liners to this plate using hose clamps and high-temperature sealant before sliding the appliance into the cavity.
4. Slide the chassis halfway in: Move the metal box slowly across your floor protector. Stop halfway into the opening to check that the gas line and power cord are not pinched against sharp corners.
5. Engage the vent collar: Push the chassis the rest of the way into the firebox until the top opening aligns with the vent plate. Engage the locking lever or secure the retention screws as directed in the manual.
6. Level the unit: Locate the adjustable leveling bolts at each corner of the base. Set a spirit level on top of the chassis. Turn the bolts with a wrench until the unit sits level and stable without rocking.

How Do You Hook Up Gas and Mount the Trim?

With the metal box leveled in place, you are ready for final utility connections, safety checks, and trim installation. Follow these steps carefully:

1. Connect the gas supply line: Attach a flexible corrugated stainless steel gas line between the manual shut-off valve and the insert inlet valve. Apply gas-rated pipe sealant or yellow PTFE tape to male pipe threads, but leave flared brass fittings dry and clean.
2. Inspect all joints for leaks: Turn on the gas shut-off valve. Brush a generous coat of commercial non-corrosive gas leak detector fluid or thick soapy water over every fitting. Watch each joint closely for several minutes. If growing bubbles appear, turn off the gas, tighten the fitting, and inspect again until the bubbles stop. Never use an open flame to check for fuel leaks.
3. Plug in electrical components: Plug the blower fan power cord into the 120-volt outlet inside the cavity. Connect any remote receiver wires or wall switches to the designated terminals on the control module.
4. Arrange the burner media: Place the ceramic log set, burner grates, and glowing embers over the burner pan exactly as shown in the manual diagram. Avoid piling embers over the burner ports, which can block airflow and cause soot buildup.
5. Mount the surround and draft seal: Stick self-adhesive fiberglass insulation strips along the back perimeter of the surround (the metal trim covering gaps around the unit). This insulation compresses against the rough brick face to seal out cold drafts. Hook the surround panel onto the chassis brackets and secure it with mounting screws.

What Accessories Help You Finish the Installation?

A smooth gas insert installation depends on several key accessories that bridge the gap between an old brick fireplace and a modern heating appliance. Gathering these items before you begin helps prevent air leaks, reduces mechanical noise, and creates a neat, finished look.

Look for these practical installation supplies when planning your project:

• Whistle-free flexible gas lines: Standard corrugated gas lines often create an annoying high-pitched whistling noise as fuel passes through the ridges. Flexible lines built with varied corrugation patterns disrupt internal vibration and keep fuel flow quiet.
• Self-adhesive fiberglass insulation strips: Applying high-density insulation tape behind your metal surround panel creates a tight seal against uneven masonry. This prevents cold outdoor air and chimney odors from seeping into your room.
• Properly sized trim kits: Old fireplace openings rarely match standard modern insert dimensions. Three-sided or four-sided metal trim panels overlap oversized gaps and blend the unit into your brickwork.
• High-heat glowing embers: Spreading loose rock wool or mineral vermiculite across the burner ports creates a realistic glowing coal bed beneath the ceramic logs.

If measuring your chimney reveals tight bends or if running new gas lines through your foundation is too costly, you have alternatives. Many homeowners choose an electric fireplace insert for large room heating instead, which slides into your existing opening and plugs straight into a wall outlet without chimney venting or gas piping.

1

Comfort Glow Vent Free Gas Fireplace Log Insert, 6 Pcs

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  9.6
• Brand
  Comfort Glow

Key specs2

Heat Output and Fuel

30,000 BTUs, dual fuel (liquid propane or natural gas)

Thermostat Operation

The manual dial adjusts between 1 and 5, shutting the burner off when target temperature is reached and relighting automatically as room air cools.

Pros & cons42

Pros

• Dual fuel support allows operation with either natural gas or liquid propane setups
• Delivers up to 30,000 BTUs of heat to warm spaces up to 1,000 square feet
• Built-in thermostatic knob offers 5 temperature settings to regulate room heat automatically
• Realistic 6-piece oak log layout provides traditional fireplace visuals without wood mess

Cons

• Requires permanently sealing fireplace ash dumps and outside air ducts before setup
• At 24.5 inches wide, it will not fit smaller or narrow hearth openings

2

Gas Fireplace Glowing Embers, Rock Wool for Vent Free or

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  9.2
• Brand
  Glowing Fireplace Embers

Key specs1

Embers Compatibility

Vented or vent-free gas log sets, inserts, and stoves

Pros & cons32

Pros

• Compatible with both vented and vent-free gas fireplaces, inserts, and stoves
• Resealable zipper bag with tear strip keeps unused rock wool clean for future touch-ups
• Provides 4 ounces of rock wool to simulate glowing embers across burner pans

Cons

• Limited to 4 ounces, which may not cover wide double-burner pans in large fireplaces
• Manufacturer specifies it must only be used with appliances designed for rock wool

3

RealFyre 18 Inch Vented Gas Fireplace Logs Kit, Natural Gas

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  9.2
• Brand
  RealFyre

Key specs2

Burner and Log Hardware

• 18-inch ceramic refractory log set reinforced with steel rods
• Natural gas burner pan with included fireplace grate
• Damper clamp, silica sand, glowing embers, and gas fittings

Fuel and Venting Type

Natural gas only, vented chimney required

Pros & cons42

Pros

• Ceramic logs are reinforced internally with steel rods for added durability under high heat
• Complete installation kit supplies the burner, grate, silica sand, embers, and damper clamp
• Hand-painted bark detailing replicates the appearance of seasoned live oak wood
• Backed by a 2-year limited manufacturer warranty on components

Cons

• Designed strictly for natural gas fuel lines and cannot run on liquid propane
• Requires an open, vented chimney setup with manual match-light ignition

4

Midwest Hearth Whistle Free Gas Flex Line for Fire Pit

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  9.0
• Brand
  Midwest Hearth

Key specs2

Gas Line Specifications

Features 3/8-inch inner diameter and 1/2-inch outer diameter stainless steel tubing with 1/2-inch flare nuts, designed to eliminate whistling noises.

Fuel Compatibility

Natural gas and liquid propane

Pros & cons42

Pros

• Multi-pattern corrugation stops high-pitched whistling vibrations during gas flow
• Stainless steel build handles indoor fireplace inserts as well as outdoor fire pits
• Compatible with both natural gas and liquid propane connections
• Standard 3/8-inch inner diameter and 1/2-inch outer diameter with 1/2-inch flare nuts

Cons

• Fixed 18-inch length provides no slack if the gas supply stub is positioned farther away
• Flare fittings must match your supply valve size or require separate step-down adapters

5

Rodalflame Fireplace Insert Trim Kit for 32.99" W x 24.92"

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  8.8
• Brand
  RODALFLAME

Key specs1

Outer and Cutout Dimensions

• Outer frame measures 41.9 inches wide by 29.5 inches high
• Inner opening measures 30.3 inches wide by 23.6 inches high
• Overall depth profile of 0.7 inches in black sheet metal

Pros & cons32

Pros

• Sturdy sheet metal construction resists warping under normal room conditions
• Covers gaps between wall openings and insert chassis for a clean finished look
• Includes all necessary assembly hardware for quick installation

Cons

• Designed only for size-matched Rodalflame fireplaces (model B0BBR1HTLN)
• Fixed 30.3-inch by 23.6-inch inner cutout cannot adjust to fit other brand inserts

6

GASPRO Gas Fireplace Embers, 10 Oz. Glowing Embers for Gas

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  8.8
• Brand
  GASPRO

Key specs2

Media Bed Composition

Combines basalt-based rock wool fibers with expandable vermiculite flakes to scatter flame points and produce deep ember glow across the burner.

Manufacturer Warranty

365 days from date of purchase

Pros & cons42

Pros

• Blend of rock wool and vermiculite creates authentic glowing and flickering coal effects
• Flaked vermiculite helps distribute gas across the burner pan for even flame coverage
• Asbestos-free mineral formula made from natural basalt, diabase, and vermiculite
• Generous 10-ounce bag provides extra material for future maintenance refresh

Cons

• Can create loose mineral dust during initial placement, requiring gentle handling
• Excessive application on burner ports can interfere with proper combustion

7

Rutland Products 1111 Fireplace Insert Insulation Fiberglass, 1-1/2-Inch by 10-Feet,

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  8.6
• Brand
  RUTLAND PRODUCTS

Key specs2

Gasket Size and Rating

1.5 inches wide by 10 feet long, rated up to 225 degrees F

Installation Seal Role

Seals the perimeter gap between the metal insert body and the masonry firebox face to block cold drafts from entering the living space.

Pros & cons42

Pros

• Temperature rated up to 225 degrees Fahrenheit for dependable insert perimeter sealing
• Integrated adhesive backing allows direct application to clean insert outer flanges
• Generous 10-foot strip covers top and side margins on standard residential inserts
• Backed by an 18-month warranty against defects in material and manufacture

Cons

• Must be replaced every time the fireplace insert is pulled out for maintenance or cleaning
• 225-degree rating means it is designed for perimeter masonry drafts, not direct firebox flame contact

8

Midwest Hearth Fireplace Insert Insulation 10' Roll w/Self Adhesive Backing

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  8.2
• Brand
  Midwest Hearth

Key specs1

Draft Sealing Dimensions

Supplies 10 feet of 1.5-inch wide dark brown fiberglass insulation strip rated to 225 degrees Fahrenheit to seal outer hearth gaps.

Pros & cons42

Pros

• Pressure-sensitive adhesive backing adheres smoothly without messy separate cements
• 1.5-inch width provides solid surface contact against rough brick or stone surfaces
• Helps stop room drafts and cold air infiltration around masonry firebox margins
• Rated to withstand temperatures up to 225 degrees Fahrenheit

Cons

• Requires replacement each time the insert chassis is pulled for chimney sweeping or service
• Masonry surfaces must be thoroughly cleaned of soot and dust for the adhesive to stick properly

9

Skyflame 18-inch Fireplace Log Grate with Dual Burner Pan and

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  7.8
• Brand
  Skyflame

Key specs2

Firebox Clearance Requirements

• Minimum front opening width: 28 inches
• Minimum rear cavity width: 21 inches
• Minimum firebox floor depth: 15 inches

Included Connection Hardware

Comes with an 18-inch 5-bar grate, dual pipe burner, 12-inch non-whistle flex connector, adapter fittings, and a damper clamp for natural gas installs.

Pros & cons42

Pros

• Built with 304 stainless steel for enhanced corrosion resistance under high temperatures
• 5-bar grate design holds gas logs firmly in place to prevent shifting or rolling
• Dual pipe burner structure distributes gas evenly for variable flame height and ember coverage
• Includes 12-inch non-whistle flex line, brass connection fittings, and chimney damper clamp

Cons

• Requires minimum firebox cavity of 28 inches front width, 21 inches back width, and 15 inches depth
• Natural gas only, requiring a match-light procedure with no remote or wall switch control

10

Frienda 8 oz Glowing Embers Rock Wool Mixed with Vermiculite

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  7.2
• Brand
  Frienda

Key specs1

Media Pack Specifications

8 oz rock wool fiber mixed with exfoliating vermiculite

Pros & cons32

Pros

• Blended mix of fiber rock wool and exfoliated vermiculite mimics active wood ember beds
• Formulated to withstand high heat inside vented gas log sets, inserts, and stoves
• 8-ounce quantity provides sufficient material to refresh burner media across several seasons

Cons

• Not explicitly rated for vent-free appliances in product specifications
• Overpacking media over gas burner ports can cause improper combustion or carbon buildup

Last update on 2026-10-02 / Affiliate links / Images, Product Titles, and Product Highlights from Amazon Product Advertising API

FAQs

Can I install a gas fireplace insert by myself?

You can handle preparatory jobs like cleaning the firebox, measuring the opening, and attaching the decorative trim surround. However, running gas supply lines, making fuel fittings, and checking combustion pressure should be left to a licensed professional. Most local building codes require certified technicians for gas work to protect your home from fire hazards and ensure insurance coverage.

Do I need an electrical outlet inside the fireplace?

Most modern gas inserts require a standard 120-volt wall outlet to power the convection blower fan and electronic ignition modules. While some models feature battery backups to ignite the flame during power outages, the blower fan needs household electricity to push heated air into your living room. An electrician can install an approved outlet inside the firebox.

What happens to the old damper during installation?

The old chimney damper must be removed or clamped permanently open. Direct-vent inserts run two flexible metal pipes through the chimney throat, and a swinging damper plate could crush or puncture those pipes. Most venting kits include a metal clamp to lock the damper blade open so it can never swing shut against the pipes.

What safety permits and inspections are required?

Most local building departments require a mechanical or plumbing permit before running gas piping or venting through a roof. Once the installation is finished, a municipal inspector reviews the gas pressure, pipe joints, and vent termination clearances to verify the work meets national fuel gas standards. Skipping permits can void your appliance warranty and cause problems when selling your home.