Conversion · Liner · Gas Insert · Eastside WA
Wood-to-gas fireplace
conversion.
Most wood-burning fireplaces on the Eastside go unused. Puget Sound burn bans, the prep and cleanup of seasoned wood, and the unpredictability of actual heat output wear people down. Converting to gas eliminates all of those — and most Eastside masonry fireplaces are stronger conversion candidates than homeowners assume. The existing firebox opening stays. The existing chimney becomes the vent path. What changes is what comes out of it.
The first question is what you’re starting with
Three starting points,
three different paths.
Eastside homes built across four decades have very different fireplace situations. Masonry fireplaces, factory-built prefabs, and homes with no existing fireplace all convert differently — sometimes to an insert, sometimes to a new direct-vent build. A walkthrough confirms which path applies before anything else.
01
Pre-1985 masonry fireplaces
The strongest conversion candidates. Full masonry fireboxes with a brick or stone surround and a masonry chimney above are standard in Bellevue’s established neighborhoods — Newport Hills, Eastgate, Somerset, Lakemont, and downtown Bellevue. A gas insert slides into the existing firebox opening; a flexible stainless liner runs up the existing chimney to handle combustion exhaust. No new exterior penetration. No new chase framing. The chimney structure stays in place.
02
1985–2005 factory-built prefabs
Factory-built zero-clearance units — a steel firebox in a framed chase with a lightweight metal chimney above — are common in Eastside homes built between 1985 and 2005. These can convert to gas, but insert selection is brand-specific: the insert dimensions have to match the existing firebox opening, and the existing chase has to be in serviceable condition. If the prefab is in poor condition or the firebox opening doesn’t accommodate any available insert, the path becomes a new direct-vent new-build.
03
Homes with no existing fireplace
No existing firebox doesn’t mean no path to gas. A new-build direct-vent gas fireplace — which vents through an exterior wall with a co-axial two-pipe system and requires no chimney — is the standard approach. The project scope is larger (new firebox opening, new venting assembly, full surround build), but it opens up format options that a conversion into an existing firebox can’t accommodate: linear wide-format units, see-through fireplaces, and fireplace placement in rooms with no chimney above.
The part most homeowners don’t expect
The liner is what
makes it safe.
When a gas insert converts a masonry fireplace, the existing chimney doesn’t just continue working as-is. A flexible stainless co-linear liner is installed from the insert collar up through the existing flue to a new crown termination cap. This liner is the dedicated vent for the gas appliance — sized to the insert’s BTU output and vent specifications, not the old wood-burning flue dimensions.
- · Why not use the existing flue? A wood-burning flue is sized for wood combustion. Gas appliances vent at different temperatures and exhaust volumes. Using an unlined flue for a gas appliance creates condensation buildup, carbon monoxide risk, and code violation. The liner provides a correctly-sized, properly-sealed vent path.
- · Chimney condition check. Before the liner is installed, the chimney is inspected for structural integrity — crown condition, flue tile condition, mortar joint integrity. Minor wear doesn’t prevent liner installation. Significant deterioration needs to be addressed first. Prime identifies any issues before the liner goes in, not after.
- · Bellevue permits cover the liner. The gas piping permit and mechanical permit required by the City of Bellevue for a gas conversion cover the full installation — including the liner. Prime includes permit fees in the fixed written estimate and pulls the permits before installation begins.
- · The chimney exterior stays intact. The liner runs inside the existing chimney structure. The masonry exterior, the crown, and the cap are replaced or repaired but not rebuilt. The chimney looks the same from outside — the change is all internal.
What the written estimate covers
Five items in every
conversion estimate.
A complete gas conversion estimate isn’t just the insert price. See a full breakdown of cost drivers here. The five items below appear as explicit line items on every Prime estimate.
The gas insert
The appliance itself — make, model, BTU output, flame presentation, and manufacturer warranty. Unit selection happens in the design conversation, before the estimate is written. We discuss the room size, heat objective, and design preference. The insert is chosen based on those inputs, not based on what’s in stock.
Stainless liner assembly
The flexible co-linear liner, sized to the insert’s venting specifications. Includes the liner itself, the connection to the insert collar, and the new crown termination cap. This is a dedicated component of the conversion — not an optional upgrade.
Gas line connection
A new gas supply branch from the nearest gas line to the insert location. For most Eastside homes, the nearest gas line is close — range, furnace, or dryer. For rooms farther from the meter, the run is longer. The estimate states the scope of gas line work explicitly.
Surround and mantel scope
Whether the surround is a simple tile face around the insert, a new mantel installation, or a full custom surround — this is the item most homeowners adjust the most during the design conversation. The existing wood-fireplace trim usually doesn’t suit a gas insert’s proportions, so most conversions include some surround work.
Permits and inspection
The City of Bellevue requires a gas piping permit and mechanical permit for every gas conversion. These are included in the estimate as a line item. Permits are pulled before installation begins. The City inspection happens before the fireplace is commissioned — not as an afterthought.
Common questions
Gas conversion,
answered.
Related
Adjacent projects.
Free in-room walkthrough
The conversion conversation
starts at the firebox.
We assess the existing firebox, confirm candidacy, and put together a fixed written estimate with every line item — insert, liner, gas line, surround, and permits — before any work begins.