Every gas or wood-burning appliance has a specific flue sizing requirement from its manufacturer, and an oversized flue, a common issue when adding a smaller insert to an old, large masonry flue, can actually cause poor draft and condensation problems rather than solve anything.
Why insert conversions almost always need a new liner
A big open masonry fireplace flue was sized for the volume of an open fire. Drop a smaller wood or gas insert into that same fireplace without relining, and the exhaust gases cool too much in the oversized space before they exit, which causes weak draft, creosote buildup in gas appliances that should not have any, and sometimes backdrafting into the room. A correctly sized liner solves this by matching the flue diameter to what the new appliance actually needs.
What we install
Stainless steel flexible liner
The most common choice for insert conversions, flexible enough to route through an existing flue’s bends.
Stainless rigid liner
Used where a straight run allows it, for maximum durability.
Cast-in-place liner
Poured in place to rebuild structural integrity in a severely deteriorated masonry flue.
Insulated liner kits
Recommended for wood-burning appliances to maintain proper flue temperature and draft.
Frequently asked questions
Do I really need a new liner if I’m just adding a gas log set?
It depends on the flue size relative to the log set’s requirements. Some gas log installations can use the existing flue; others, especially in oversized older fireplaces, need relining for safe, efficient operation. We’ll assess your specific setup.
How long does a full reline take?
Most flexible liner installations are completed in a single day, including connecting the new liner to the appliance and sealing the top.
Will relining reduce my fireplace’s opening size?
The liner runs inside the existing flue, not the firebox opening, so it does not change how the fireplace itself looks or how large a fire you can build in an open masonry setup.
Is a cast-in-place liner more expensive than stainless?
Generally yes, since it’s used specifically for structural rebuilding rather than routine relining, but it’s the right call when the masonry itself has deteriorated significantly.