Chimney Liners

What a liner does

A chimney's flue is the open passage exhaust travels through. The liner is what forms the walls of that passage. It has three jobs: contain heat so it doesn't reach nearby wood framing, resist the corrosive moisture in exhaust, and give the appliance a passage of the right size and shape to draft well.

Older New Jersey homes most often have clay tile liners, stacked in sections with mortar joints. Some very old chimneys have no liner at all. Our guide to flue vs. liner explains the terms and what "unlined" means.

When a liner needs attention

• Damage. Cracked, shifted or missing tiles, open joints, or damage after a chimney fire.
• A new appliance. A wood stove, insert, or new furnace or boiler often needs a liner sized for it.
• Condensation. Staining or dripping from a flue that vents a gas or oil appliance, often in cold weather.
• An orphaned water heater. When a furnace is replaced with a high-efficiency unit vented elsewhere, the water heater may be left alone in a flue that's now too large. See the orphaned water heater problem.
• No liner. An unlined masonry flue.

How we assess it

Liner decisions depend on what's actually inside the chimney, so the camera does most of the work here. We run a chimney camera through the flue where it allows, recording the condition of each tile and joint, any offsets, and the flue's size. We note which appliance or appliances the flue serves and check their venting requirements. From the roof, when it's safe, we measure the flue top and look at the crown. Where it's safe and accessible, we check the chimney's path through the attic.

You get photos or footage and our findings. If the flue can be repaired rather than relined, that's part of what we show you.

Liner types compared

We install all three types: stainless steel, cast-in-place and clay tile. The choice comes from the appliance, the fuel and the condition and shape of the flue, so the recommendation follows from what the assessment finds.

Our guide to stainless, cast-in-place or clay liners compares them in depth.

Sizing for wood, gas and oil

A liner has to suit the appliance as well as fit the chimney. Too large, and exhaust cools and moves slowly, which causes creosote in wood systems and condensation in gas and oil systems. Too small, and the appliance can't vent its exhaust properly.

• Wood stoves and inserts are sized using the stove manufacturer's instructions. Many stainless liner systems for solid fuel are listed with insulation, and CSIA notes that liners serving solid-fuel appliances require insulation.
• Gas appliances are sized using the appliance manufacturer's and venting tables. Insulation isn't always required but can help performance.
• Oil furnaces and boilers need a liner rated for oil exhaust, which is acidic and sooty. See oil furnace and boiler flues.

If two appliances share one flue, both have to be accounted for. Often each needs its own liner.

Repair or reline?

Not every damaged clay liner needs to be replaced. When the tiles are intact but have gaps, open joints or limited cracking, resurfacing or joint repair can sometimes restore them. That's covered on our flue repair page, and compared in flue resurfacing vs. a new liner.

Relining is usually the better choice when:

• Tiles are badly cracked, displaced or missing
• The flue is the wrong size for a new or existing appliance
• The chimney is unlined
• A new stove or insert needs a direct connection from the appliance to the top

How a relining job usually goes

1. Sweep and cameraThe flue is cleaned and recorded so we know its true size, offsets and condition.
2. Size and selectThe liner type, diameter and any insulation are chosen from the appliance and liner manufacturers' requirements.
3. Prepare the flueIf the existing tile is too tight or broken for the new liner to pass, it may need to be removed.
4. Install and connectThe liner is run through the chimney and connected to the appliance at the bottom and to a cap at the top.
5. DocumentPhotos show the installed liner, the connections and the top.

Limits and what affects the scope

• Flue height, size and offsets
• Whether the old tile has to be removed to fit the new liner
• Fuel type and the appliance's venting requirements
• Insulation requirements
• Number of appliances sharing the chimney
• A permit may be required for appliance and liner installations, depending on your municipality

A liner protects the inside of the chimney. It won't fix leaking brick, flashing or a cracked crown on the outside.

Next step

If you're adding or replacing an appliance, have cracked tiles, or have signs of condensation, request an assessment. Tell us what appliances use the chimney. A team member will contact you to confirm a time.

Request a liner assessment

Questions homeowners ask

Sources

1. CSIA: Frequently asked questions