Southcenter / Tukwila, WA — King, Pierce & Snohomish
Gas Fireplace Insert Installation
Your old wood-burning fireplace can become a clean, efficient gas fireplace without touching your surround or mantle. We install gas fireplace inserts the right way — properly lined, code-compliant, and built to last.
What Is a Gas Fireplace Insert?
A gas fireplace insert is a sealed gas appliance that slides directly into your existing masonry or prefab firebox. Think of it as dropping a high-efficiency gas unit into the shell of your old fireplace — you keep your surround and mantle exactly as they are, but you get all the convenience and warmth of modern gas.
- ✓ Fits your existing firebox — the insert slides into the opening you already have, no major construction required
- ✓ Sealed combustion unit — unlike an open hearth, a gas insert contains combustion gases and pushes warm air efficiently into the room
- ✓ Uses your existing chimney flue with a liner — a flexible stainless steel liner runs up through your existing flue, so your chimney still does its job safely
- ✓ Far more efficient than an open hearth — open wood fireplaces lose most of their heat up the chimney; a gas insert delivers that heat into your living space
Why a Gas Insert Works in Your Existing Firebox
A gas insert is engineered specifically to slide into a wood-burning firebox opening. You're not doing a gut renovation — you're upgrading what's already there.
It fits without structural changes
The insert drops into your existing firebox opening. We add a surround trim kit that covers the old frame cleanly — no drywall work, no framing, no tile demo in most cases.
The liner is sized to the insert
We run a dedicated stainless liner down your existing flue, sized specifically to the insert's venting requirements. This is what makes the system safe and code-compliant — not an afterthought.
Sealed combustion, real heat output
Unlike open gas logs, the insert is a sealed unit. Combustion air is drawn from outside, exhaust goes back out the liner — almost all of the BTUs stay in your room, not your flue.
Looks like it was always there
Quality inserts ship with custom surround panels that give the finished installation a built-in look. Most homeowners can't tell it was retrofitted.
Deciding between an insert and other gas options? We break down all the conversion routes — inserts, gas logs, full conversions — on our Wood to Gas Fireplace Conversion page.
Is a Gas Insert Right for You?
A gas insert is one of the most practical fireplace upgrades we install. Here are six situations where it's usually the right call:
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You have an old wood-burning fireplace you rarely use — because it's too much work to maintain, and a push-button gas fire is what you actually want.
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You want gas convenience without a remodel — a gas insert fits your existing opening, so you keep your surround, mantle, and hearth exactly as they are.
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✓
You want to keep your existing fireplace surround — the insert trim panel fits flush against your current facing, so the finished look is clean and intentional.
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You're done hauling wood and cleaning ash — gas inserts eliminate creosote buildup, ash cleanup, and the hassle of keeping a wood supply stocked and dry.
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✓
You want real heat output, not just ambiance — inserts are rated for efficient room heating and can meaningfully reduce how hard your HVAC works in the space where the fireplace lives.
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✓
Your old masonry fireplace is drafty — the sealed combustion chamber in a gas insert eliminates the cold air infiltration that open-hearth fireplaces are notorious for when not in use.
Our Gas Insert Installation Process
Every gas insert installation we do follows the same four steps — no shortcuts, no guesswork.
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1
Firebox Assessment
We check your firebox dimensions, masonry condition, and flue to nail down the right insert size and venting approach. Fit matters here — a properly sized insert performs better and looks intentional, not crammed in. If there's anything going on with the masonry or flue that needs attention first, we'll tell you before we recommend anything.
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2
Liner & Prep Work
We run a flexible stainless steel liner down through your existing chimney flue — this is standard on every gas insert install, not an upgrade. We also prep the gas connection and confirm your existing line has enough capacity. If a new line or capacity upgrade is needed, we coordinate that before installation day. No surprises when we show up.
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3
Insert Installation
We set the insert into the firebox opening, connect it to the liner and gas supply, and fit the surround trim flush against your existing facing. We protect your hearth and mantle throughout, and we don't call it done until the trim is seated properly and the unit sits right in the opening — not just close enough.
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4
Testing & Commissioning
We run the insert through a full test — ignition, flame adjustment, blower, controls — and confirm there are no leaks and that the venting is drawing the way it should. Before we leave, we walk you through how everything works: the remote or wall switch, flame height, thermostat features, whatever your model has. You shouldn't need to figure anything out on your own.
Who Installs Gas Fireplace Inserts?
A gas insert install crosses three trades — gas line work, chimney lining, and appliance fitting — so the right installer is a licensed gas fireplace contractor, not a general handyman or a chimney-only company. The gas connection must be made and leak-tested by a licensed technician, the stainless liner has to be sized to the insert's venting spec, and the unit itself needs to be set and sealed per the manufacturer's manual to keep the warranty valid.
That's the work we do every week. We're a licensed, insured gas fireplace company based at Southcenter in Tukwila — we handle the insert, liner, gas connection, surround panels, and permits as one job, so nothing falls between trades.
What Affects Gas Insert Installation Cost
Every firebox is different, so we quote each job individually — estimates are free. What moves the number:
The Insert Itself
Quality direct-vent insert units generally run $4,000–$6,000+ before installation, depending on size, configuration, and finish — premium linear and oversized models run well beyond that.
Liner Run & Venting
The stainless liner is sized to the insert and run the full height of your chimney — a taller chimney or a flue that needs prep work adds material and labor.
Gas & Electrical
If the firebox already has a gas stub, connection is simple. Extending a line — or adding the outlet most blower kits need — adds scope. We tell you exactly what's required at the estimate.
Surround & Finish
Standard surround panels are included with most units; oversized openings or custom trim add cost. Liner, gas, electrical, and labor are quoted per job — free estimate, firm number before work starts.
Want a real number? Get a free estimate — firm quote before any work starts.
Service Area
Based at Southcenter in Tukwila, we install gas fireplace inserts throughout King County, Pierce County, and Snohomish County — including Seattle, Bellevue, Renton, Kent, Federal Way, Auburn, Kirkland, Tacoma, Everett, and the surrounding communities.
Frequently Asked Questions
What is a gas fireplace insert?
It's a sealed gas appliance that fits directly into your existing masonry or prefab fireplace opening. It takes the place of your open hearth with an enclosed, efficient gas unit — real flames, reliable heat, push-button convenience — without touching your surround or mantle. The insert connects to a flexible stainless steel liner that runs up through your existing chimney flue, so the structure stays put and the installation is far less disruptive than building from scratch. Most homeowners are genuinely surprised how clean the job is.
Will a gas insert fit in my existing fireplace?
In most cases, yes. We measure your firebox carefully during the initial assessment and match it to an insert that fits the way it's supposed to. Inserts come in a wide range of sizes — compact prefab openings to big masonry hearths — so there's usually something that works. Every now and then a firebox has unusual dimensions or a structural problem that limits the options, and we'll tell you that plainly before anything is ordered or scheduled.
Do I need to keep my chimney for a gas insert?
Yes — your chimney stays put. A gas insert uses a flexible stainless steel liner run inside your existing flue to carry combustion gases safely to the outside. The liner goes through the chimney, not around it, so your footprint doesn't change and the installation is far less invasive than starting fresh. The liner is sized specifically for gas appliances, so it vents correctly even if your original flue was built for a wood-burning fireplace.
How much does a gas insert installation cost?
The unit is the biggest variable — quality direct-vent inserts generally run $4,000–$6,000+ before installation, with premium linear and oversized models well beyond that. Total installed cost depends on liner length, gas line work, and surround finish, so every job gets a free estimate with a firm number before work starts.
Is a gas insert more efficient than a regular gas fireplace?
Yes, significantly. Gas inserts are sealed units with high efficiency ratings — many are 70–80% or better, which means most of the heat they produce actually stays in your room. An open-hearth wood fireplace loses well over half its heat straight up the chimney. If you want to actually warm a room instead of just watching a fire, an insert is one of the most efficient ways to do it. And compared to a natural-vent gas fireplace — which exhausts through an open flue — the insert's efficiency advantage is real if heating output matters to you.
How long does a gas insert last?
With proper maintenance, 15–25 years is a realistic lifespan. The parts that wear — thermocouple, igniter, gas valve — are all serviceable components. They get replaced as needed, not the whole unit. The biggest thing that affects how long an insert lasts is whether it gets serviced regularly. Annual tune-ups catch small problems before they turn expensive and keep the unit running efficiently. Most of the inserts we service are in great shape well into their second decade.
Ready to Convert Your Fireplace?
Call or text to schedule a free assessment. We'll come out, measure your firebox, walk you through what fits, and give you a straight upfront estimate.
Related Services
Gas Fireplace Installation
New gas fireplace installations for any space.
Gas Log Set Installation
Prefer an open hearth? A vented or ventless log set is the simpler alternative to an enclosed insert.
Wood-to-Gas Conversion
Convert your wood-burning fireplace to gas.
Gas Fireplace Services
Repair, maintenance, and all gas fireplace work.