How to Install a Flue Liner Like a Pro

You’ll need to know what diameter flue liner you need to buy. If you have a wood stove or a fireplace insert, you can find the liner diameter in the user manual. Otherwise, you should consult with a chimney flue liner pro to determine what diameter liner is best based on your fireplace size and the size of your insulation blanket that will attach to the liner.

After consulting with the user manual or a chimney liner installation pro, you’ll need to measure the length of the chimney, from the top of the chimney crown, which is the concrete, metal, or stone slab at the top of the chimney opening on the roof, all the way down to the connector on the wood stove or fireplace insert or to just above the open fireplace.

You’ll need to note down the diameter and length to purchase the correct flue liner materials. Add about 12 inches to the length total when buying the liner to give yourself some wiggle room.

Head to a home improvement store or order the appropriate flue liner materials when working with a professional chimney installer. For DIY flue liner installation, the easiest option is typically a flexible stainless steel or aluminum flue liner kit. 

Just keep in mind that some materials may not work for all fireplace types and DIY kits often don’t last as long as professionally installed flue liners. For instance, aluminum flue liner kits only last about five years and are only suitable for use in gas fireplaces.

In addition to the flue liner, you’ll need to purchase blanket or pour-in insulation. Blanket insulation is recommended if you have more than a 2-inch gap between the liner and the chimney walls, while pour-in insulation is better for gaps under 2 inches.

Roll out the flue liner from its coil into a straight line and secure it that way with a hose clamp. Gently tighten the clamp with a wrench, but don’t overtighten, or you’ll damage the liner.

To add blanket insulation, measure the circumference of the bottom termination connector, where the flue liner will stop. Then, multiply that measurement by 3.14 (or pi), and add about 1 more inch to make sure you have enough insulation. Apply a spray adhesive on the liner to attach the blanket insulation.

When the insulation is fully applied, you can unclamp the liner and use foil tape to close the seam along the side of the flue liner. The installation kit will include wire mesh to protect the liner and installation from damage during installation. You can now cover the liner with the mesh and use a wrench and hose clamps to hold it in place at the top and bottom of the flue liner. Trim excess wire mesh that extends past the flue liner.

For pour-in insulation, follow the product’s instructions to apply the insulation.

You’ll need a ladder to access the roof, and you’ll need to recruit a friend or neighbor to help with the following steps. If you’re not comfortable getting on the roof to place the flue liner inside the chimney, now is a great time to call in a pro for assistance.

Attach a rope to the flue liner’s bottom connector and climb up the ladder to the roof. Have a friend on the ground start to carefully push the flue liner up to you until you have the liner and the bottom connector, rope included. Now, that friend should head indoors to the fireplace or wood stove area. 

You’ll carefully drop the rope down the chimney to your friend. Then, with the bottom connector centered in the chimney opening, start lowering it down while the person at the bottom guides with the rope to avoid snagging the liner on the inside of the chimney. Continue until the bottom connector is where the flue is set to stop, and clip any excess at the top of the flue liner, leaving at least 4 inches of liner above the chimney crown.

If you are installing a flue liner that will connect to a wood stove or fireplace insert, position that appliance against the flue liner to make sure it will fit properly before securing the top of the flue liner to the chimney crown.

Ask your helper to hold the bottom of the flue liner steady in place while you secure it at the top. To secure the flue liner, apply silicone caulk and then quickly press the chimney top plate down over the flue liner top to seal it with the caulk.

Attach the flue liner and top plate to the chimney with a quick-connect clamp and masonry screws. If you are dealing with concrete, use concrete screw anchors, such as Tapcon brand screws, to hold the liner and top plate in place before you install the flue cover.

If you have a flue cap or cover, which can help keep pests, rain, and debris out of the chimney, install it over the top plate of the chimney with silicone caulk.

For a wood stove or fireplace insert, you’ll need to connect the flue liner to the appliance. Place the stovetop adaptor into the appliance, and use clamps to attach it to the liner. Or, you may need to use tin snips to attach a tee body to the tee snout at the base of the flue liner, depending on the type of fireplace you have and the flue liner you are installing. For a tighter seal, you can also apply furnace cement by following the cement product instructions.

Once the flue liner is installed, make sure the flue is open, and then you’ll be ready to enjoy the warmth of your fireplace.