What a chimney liner does and why the type matters
A chimney liner keeps heat and combustion gases inside one continuous passage from the appliance to the top of the chimney, so they reach the outdoors instead of the framing or the room. The liner type decides what fuel the flue can safely carry.
Our chimney liner installation page covers the job itself and the posted starting price. This guide is the comparison: what each liner material is, where it belongs, and the questions to ask before anyone quotes you a reline.
The Chimney Safety Institute of America’s written Level 1 procedure tells the sweep to make sure the chimney is appropriate for the appliance, and Portland’s permit guide for stoves says a wood stove vents through a listed metal chimney or a lined masonry chimney. Those two sentences are the whole case for liners.
Clay tile liners are the common original liner
Clay tile is the original liner: fired clay sections stacked inside the brick and set in refractory mortar at the joints as the chimney went up. It is common, rigid, and handles heat well until something cracks it.
Three things crack tile: the heat shock of a chimney fire, settlement and movement of the stack, and water that gets behind the tile through an open crown or joint and freezes. A cracked or shifted tile opens a path for heat and gases into the chimney wall, and the camera is how it gets found.
In Portland the first question is whether there is any tile at all. Many brick chimneys built before the 1930s were never lined, and the Census Bureau counts over a quarter of the city’s homes as built before 1940, so a bare brick flue is no surprise in an older Portland house. Our unlined brick chimney page covers what that means.
Stainless steel liners, flexible or rigid, and what the grade means
A stainless steel liner is a metal flue run down the existing chimney, connected to the appliance below and to a top plate and cap above. It is the usual Portland reline because it suits a flue that is unlined, cracked or oversized.
Flexible liner is corrugated and comes as one continuous length, so it follows the offsets that old chimneys often have and leaves no joints inside the flue. Rigid liner is smooth-walled pipe in sections, which drafts and cleans a little better, but it only fits a straight flue.
The grade matters as much as the shape. One liner manufacturer lists both its 304 and 316 flexible liners for wood, non-condensing gas and oil appliances, and recommends the 316 where more corrosion resistance is wanted, such as a coal stove. Ask which grade is quoted and what the manufacturer lists it for.
A stainless liner for a wood stove or insert also rides along with the appliance’s own permit. Portland requires a mechanical permit and a city inspection to install a stove or insert, and the venting is part of what that inspection covers.
Aluminum liners are for certain gas appliances only
Aluminum liner is a light, thin flexible liner that belongs only where both the liner’s listing and the gas appliance’s manual allow it. It is not a liner for wood, pellets or oil.
One manufacturer lists its aluminum liner for natural gas and propane appliances with a draft hood, such as furnaces, boilers and water heaters, and for appliances listed to use a Type B gas vent. The cost guides treat it as the budget option. For a gas appliance in an old masonry chimney we quote stainless first and treat aluminum as the exception both listings have to approve.
One place aluminum turns up is an older gas furnace or water heater flue. If a high-efficiency furnace has since left the water heater alone in that chimney, the liner size is usually wrong as well as the material; the orphaned chimney guide explains the fix.
Cast-in-place liners rebuild the flue from the inside
A cast-in-place liner is a poured masonry flue formed inside the old chimney: a special refractory mix is poured around a form set down the flue, the form comes out once the mix sets, and the result is one passage with no tile joints.
Its strength is structural. A poured liner can reinforce a weak chimney and serve any heating appliance, though it cannot be taken back out later. The tradeoff is a smaller flue, a longer job, and a price near the top of the reline range.
The four liner types side by side
The table sums up what each liner is made of, where it belongs, what tends to go wrong with it, and how the trade treats it in an old Portland chimney.
| Liner | Made of | Belongs with | What goes wrong | Notes |
|---|---|---|---|---|
| Clay tile | Fired clay sections mortared at the joints | Open masonry fireplaces built with it; older furnace flues | Cracks from heat shock, settlement and water; open joints | Hard to replace in kind; usually relined with stainless or cast in place |
| Stainless, flexible | Corrugated one-piece 304 or 316 stainless | Wood stoves and inserts, gas and oil appliances as listed, unlined or cracked flues with offsets | Kinked during install, wrong grade for the fuel, left uninsulated | The usual Portland reline; insulated for wood |
| Stainless, rigid | Smooth sectional stainless pipe | Straight flues, often furnace and water heater runs | Joints, if poorly assembled | Drafts and sweeps well; only for a straight flue |
| Aluminum | Thin flexible aluminum | Certain draft-hood gas appliances, only where the listings allow | Used outside its listing; not for wood, pellets or oil | The exception, not the default |
| Cast in place | Poured refractory mix formed inside the flue | Rough or structurally weak masonry flues, open fireplaces kept as fireplaces | Smaller flue, longer job, cannot be removed | Can reinforce a weak chimney |
Sizing: the liner has to match the appliance
A liner is sized to the appliance it serves, not to the chimney it runs through. Too small and the fire will not draw; too large and the exhaust cools, slows, and condenses before it reaches the top.
The appliance’s installation manual sets the liner size, and part of a liner’s job is shrinking an oversized flue to fit. That is the reason an insert gets its own liner instead of exhausting into the open fireplace flue around it, and the reason a lone water heater struggles in a flue built for a furnace too.
Sizing is settled by the camera inspection, not the brochure. CSIA’s written Level 2 procedure recommends a Level 2 inspection before a chimney is lined or relined, and the camera run also finds the offsets, cracked tile and mortar lumps a flexible liner has to pass. The inspection levels guide covers the rest.
Insulation, and why a Portland liner usually gets it
Insulation around a stainless liner keeps the flue gases warm all the way up, which means stronger draft, less condensation and less creosote. CSIA’s homeowner guidance says liners serving solid-fuel appliances need to be insulated.
Portland chimneys earn it. A masonry stack on an outside wall sits in rain for the better part of five months a year and runs cold, and a cold flue is a creosote flue. CSIA names blanket insulation or an expanded mica or masonry insulation, and some liners come double-walled with the insulation built in.
Which liner fits which Portland situation
Match the appliance to the liner before comparing quotes, because the appliance decides the material, the grade and the insulation, and the chimney only decides how hard the install will be.
- A wood insert going into an open brick fireplace. Insulated flexible stainless, sized to the insert’s outlet, run from the insert collar to a new top plate and cap; the fireplace insert page explains why the insert cannot exhaust into the old flue.
- A freestanding wood stove venting into a masonry chimney. The same insulated stainless, plus a look at the connector pipe and thimble for clearance; the stove and its venting go through the city permit together.
- An unlined older fireplace flue that will stay an open fireplace. A stainless liner sized to the firebox opening if the flue has room, or a cast-in-place liner that tightens the brick as well.
- A gas furnace or water heater in an old brick flue. Stainless listed for gas, sized to the appliance load; the furnace and water heater flue page covers that chimney.
- A gas insert set into a fireplace. The vent kit the manufacturer lists for that model, run the way its manual says; the gas fireplace and insert page covers what a sweep checks on it.
What a liner costs, in rough terms
A stainless reline is a mid-sized chimney job: more than a sweep and a cap put together, far less than a rebuild. The exact number depends on length, offsets, insulation and the connection at the bottom.
Our posted starting price for a stainless liner covers a typical single flue; longer runs, insulation and tile removal are quoted after the camera run. The chimney sweep cost guide puts liner work next to the other common repairs so you can see the whole board at once.
One rule holds for every liner type: a flue that failed its inspection stays cold until the new liner is in and the system has been looked at again. Keep a carbon monoxide alarm near the appliance in the meantime, since a blocked or failed flue is one of the ways the CDC says carbon monoxide reaches a house.