Choosing a Chimney Liner: Material, Size, Insulation and Termination

The size the appliance requires, which comes from its documentation, not from the chimney's dimensions. Fitting larger because there is room is the most common and most consequential mistake in relining.

Draft depends on flue gases staying warm and moving. A passage larger than the appliance needs lets them expand, slow and cool, which produces weak draft, smoke returning into the room and creosote forming much faster.

The one appropriate to the fuel being burned, because wood, gas and oil produce different corrosive by-products. A specification question worth asking directly, since it is invisible once installed and it determines the liner's real life.

Often, and especially on an exterior chimney in this climate. It keeps gases warm enough to draft correctly, reduces creosote, and can be what allows a required clearance to be met where the chimney passes through framing.

The chimney decides. Rigid sections suit a straight run and have a smoother interior. Flexible negotiates offsets. A question of what the flue geometry allows instead of a preference between two grades of product.

It stays if there is room for the correct liner diameter inside it, and it is broken out if there is not. Legitimate work and it belongs in the scope explicitly, since a quote silent on it may be planning an undersized liner instead.

The alloy relative to the fuel, how the appliance is run, and whether it is kept clean. A correctly specified liner is a long-term component; one in the wrong alloy for the fuel is not, and it fails from the inside.

It fixes a draft problem caused by an oversized, leaking or cold flue, which covers a large share of them. It does not fix one caused by house pressure, a blocked cap, a short chimney or a fireplace opening out of proportion to its flue. Diagnose first.

As a general matter, appliances need their own flue, and connecting two into one is a serious finding, not an economy. Where anyone proposes it, that is a question to put to the technician explicitly and get answered in writing.

The installation should be documented and the appliance connection checked as part of the job. Keep that documentation: it tells the next technician and any insurer what is inside the chimney, which is otherwise unknowable.

Material and grade, diameter, whether it is insulated, how it terminates, and what happens to the existing tile. With those five stated you can compare. Without them you are comparing two numbers attached to unknown work.

Less than people expect. Most of the work happens at the top of the chimney and at the appliance connection, and it is commonly a matter of a day or so on a straightforward chimney instead of a building project.