By Daniel Watkins, Noble Chimney Sweepers.
A wood or pellet insert dropped into an existing masonry fireplace needs its own full-length liner running from the insert all the way to the top of the chimney. This is the single most common corner cut we find on inserts installed by a previous owner, and it is not a minor omission. Without that liner the appliance cannot vent the way it was designed to, and the chimney it is sitting in was never built for what an insert produces.
Why the original flue is the wrong size
An open fireplace throws most of its heat up the chimney, and that hot gas is what drives the draft. An insert is built to do the opposite: it holds heat in the room, which means the exhaust leaving it is far cooler and much smaller in volume than the flue above it was sized to carry.
Put cool, slow exhaust into a large masonry flue and it loses temperature fast against all that cold brick. Slow, cooling smoke is exactly the condition that condenses creosote, so the flue loads up quickly, often in a fraction of a season. A correctly sized stainless liner keeps the exhaust hot and moving, which is why it is the fix rather than an upsell.
The gap nobody sees
There is a second problem, and it is the reason a partial connector is not good enough. When an insert vents into a short piece of pipe that stops at the smoke chamber, the space around and above it becomes a dead cavity. Smoke and creosote collect in there, out of reach of both the insert and any normal cleaning, and the deposits sit in the least accessible part of the chimney.
That cavity is also unreachable during a routine sweep, which means a chimney can be swept every year and still be carrying a hazard nobody has laid eyes on. A liner eliminates the cavity entirely by carrying exhaust in one continuous path from the appliance to the cap.
How to tell what you have
Open the insert and look up past the baffle with a flashlight, or look down from the top of the chimney. If you see a metal pipe running continuously upward, you likely have a liner. If the pipe ends a short distance above the appliance and opens into brick, or if you can see the original clay tile flue, you do not.
Two other clues point the same way. Creosote building up unusually fast, or a stubborn smoky smell in the room when the insert is cold, both suggest exhaust is lingering in a space it should not be in. Either way this is best confirmed during a chimney inspection, where the flue can be viewed along its full length rather than guessed at.
What a proper installation includes
A correct setup is a continuous stainless liner sized to the appliance outlet, insulated where the manufacturer calls for it, positively connected to the insert at the bottom, and terminated with a top plate and cap. Insulation matters more here than people expect, because it is what keeps the exhaust warm enough to draft in an exterior chimney through a January cold snap.
It also makes the system serviceable. Sweeping a lined insert is straightforward. Sweeping an unlined one means pulling the appliance out. That difference shows up every year for the life of the installation.
The work itself falls under chimney relining, and every job is quoted before it starts, with rates on our pricing page. Homeowners booking chimney inspection and relining in Lemont often find out an insert they inherited with the house was never lined at all. Noble Chimney Sweepers is certified, bonded and insured, owner-operated, and I have 14 years in this trade. Call (708) 432-5747, 7 days a week, 7 AM to 7 PM.
Frequently asked questions
Does a fireplace insert really need its own liner?
Yes. Insert manufacturers specify a continuous liner from the appliance to the top of the chimney, and the appliance cannot vent as designed without one.
What happens if an insert has no liner?
Cool exhaust enters an oversized masonry flue, loses heat, and deposits creosote quickly. Smoke also collects in the dead space around the connector, where no routine cleaning can reach it.
How can I tell whether my insert is lined?
Look up past the baffle with a flashlight, or look down the chimney from the top. A continuous metal pipe means a liner. Pipe that ends in open brick or a visible clay tile flue means there is none.
Does the liner need to be insulated?
Follow the manufacturer specification. Insulation is especially important on exterior chimneys, where an uninsulated liner cools fast and drafts poorly in deep cold.
Can I line the chimney myself?
We would not recommend it. Sizing, insulation, the connection to the appliance, and the top termination all have to be right together, and mistakes here affect how the appliance vents.
Is a pellet insert different from a wood insert?
The venting requirements differ in the details, but the principle is the same. Both need a dedicated, correctly sized vent path rather than an open masonry flue.
Will lining it make the insert work better?
Usually noticeably. Better draft means easier starts, less smoke rolling into the room when you open the door, and slower creosote buildup between sweeps.
How do I find out what my chimney needs?
Have the flue inspected along its full length so the liner situation is confirmed rather than assumed. Call (708) 432-5747 to book in Lemont or nearby, 7 days a week, 7 AM to 7 PM, with the price quoted up front.
Published September 6, 2026