Chimney Relining Ontario 2026: Stainless Steel Liner Cost, When a High-Efficiency Furnace Forces It, and WETT Inspection

When Chimney Relining Is Required

An existing masonry chimney needs relining in one of four specific scenarios. If none of these apply, the chimney is probably fine and a contractor pushing a $4,000 liner retrofit is selling something the house does not need.

The first scenario is a deteriorated clay tile liner. Traditional Ontario masonry chimneys use clay tile inside the brick shell as the actual flue. Clay tile cracks from freeze-thaw, from thermal shock, and from the acidic condensate of modern appliances. Once the tile is cracked, flue gases can leak into wall cavities or adjacent rooms. Spalling brick and pieces of tile falling into the firebox or clean-out are the visible symptoms.

The second is an oversized flue after appliance replacement, which is the scenario this guide focuses on and which captures most of the retrofit work happening in Ontario right now. CSA B149.1, Canada's natural gas and propane installation code, requires that venting systems be sized correctly for the connected load. Replace a furnace and leave a water heater on the same chimney, and the connected load drops by more than half, which makes the existing flue too large.[2]

The third is converting a fireplace or solid-fuel appliance to a new use, such as installing a wood-burning stove or pellet stove in a fireplace that previously burned only firewood. CSA B365 governs solid-fuel-burning appliance installations in Canada and specifies liner requirements for inserts, stoves, and factory-built chimneys.[3]

The fourth is a chimney fire or flue gas event. If you have had a chimney fire in a wood-burning system, or a backdrafting event with a gas appliance, the chimney must be inspected and usually relined before it is put back into service. The Ontario Fire Code, O. Reg. 213/07, requires chimneys and flues serving fuel-burning appliances to be maintained in safe operating condition, and municipal inspectors commonly cite relining as the fix after a documented incident.[5]

Furnace Upgrade Triggers Relining

Ontario's push toward high-efficiency heating is the single biggest driver of chimney relining work right now. A 90%+ AFUE condensing gas furnace extracts so much heat from the combustion gases that the flue exhaust comes out cool, wet, and acidic. It cannot vent into a masonry chimney. Instead, it vents sideways through a wall using PVC or polypropylene pipe, typically 2 or 3 inches in diameter.

That is an unambiguous improvement for the furnace itself. Combustion efficiency goes from around 80% to 96%, annual gas consumption drops, and Natural Resources Canada's own high-efficiency furnace guidance explicitly frames the switch as both an energy and an emissions win.[7] But it creates a second-order problem for the chimney, because most Ontario homes built before 2010 had a shared flue arrangement: the 80% AFUE furnace and the natural draft gas water heater both dumped their exhaust into the same masonry chimney.

When the furnace moves to sidewall venting, the water heater is left alone on a chimney sized for two appliances. This is the root of the retrofit spend and the reason so many post- upgrade homes end up relining within a year or two of the furnace install.

The Orphaned Water Heater Problem

A natural draft gas water heater (the common rental or older purchased unit with a metal draft hood sitting on top) vents by buoyancy. Hot combustion gases rise, create a pressure difference, and pull fresh air in through the burner. That system works only if the chimney is the right size for the load it is carrying.

On a correctly sized chimney, the water heater's flue gases stay hot enough to rise all the way to the chimney top before they cool and condense out. On an oversized chimney, the gases cool partway up, condensation forms on the tile, and that condensate is mildly acidic because modern natural gas combustion produces nitric and sulfuric compounds in small quantities. Over a few years of winters, this acidic condensate eats the mortar joints, cracks the clay tile, and attacks the brick.

Three things can go wrong beyond the chimney damage itself. First, draft can fail entirely and the water heater can backdraft, spilling carbon monoxide into the basement. Second, the chimney cap can ice over in January because the condensate is refreezing near the top, which further blocks the already marginal draft. Third, chunks of tile and mortar can fall down the flue and physically block the water heater exhaust.

The fix has exactly two options. Option one is to install a properly sized stainless steel liner inside the existing chimney, sized per the CSA B149.1 venting tables for the water heater alone. This costs $1,500 to $3,500 installed, and is the most common solution.[2] Option two is to replace the natural draft water heater with a power-vent or direct-vent model that vents sideways through a wall using PVC, abandoning the chimney for combustion use entirely. This costs $2,500 to $4,500 for the tank plus install and eliminates the chimney concern for the water heater.

A good HVAC contractor will raise this issue during the furnace quote, not after the old furnace is already on the truck. If you are getting furnace quotes in Ontario and nobody has asked about your water heater, add that question before you sign anything. See HVAC Replacement Cost Ontario for full furnace pricing and Water Heater Cost Ontario for power-vent and direct-vent alternatives.

Stainless vs Clay Tile vs Cast-in-Place

Once you know the chimney needs relining, the material decision narrows to three real options.

Stainless Steel Flexible Liner

A flexible stainless steel liner is pulled down the chimney from the top, connected to the appliance at the bottom, and terminated with a top plate and rain cap. Install is typically one day for a competent crew. Material costs run $400 to $900 for the liner, top plate, rain cap, and connectors. Labour adds $1,100 to $2,600 depending on chimney height, complexity, and access.[8]

The alloy matters. 304 stainless is adequate for wood-burning applications where the flue gas is hot and dry. 316 or 316L stainless is preferred for gas appliances because it resists the acidic condensate much better. Most reputable installers in Ontario use 316L as their default and carry lifetime limited warranties on the liner itself.

Insulation wrap around the liner is required in some configurations (particularly for wood) and strongly recommended for gas when the existing flue is large relative to the new liner. The wrap keeps the flue gases warm on the way up, improves draft, and reduces condensation. Expect to pay $300 to $600 extra for wrap on a standard two-storey chimney.

Clay Tile Replacement

Clay tile is the original technology in most Ontario masonry chimneys. Replacing cracked tile requires partial dismantling of the chimney from the top, sectional replacement, and repointing. A mason can do this, but it is expensive and invasive: $5,000 to $12,000 is typical, depending on chimney height and extent of damage. Clay tile replacement makes sense only if the chimney serves a masonry fireplace that must look original, or if the chimney structure itself is in good shape and just needs new tile.

Cast-in-Place

Cast-in-place systems (Ahrens, Supaflu, GuardianCF and similar) use an inflatable form lowered down the chimney. A cementitious mix is poured around the form, cures, and leaves a seamless round flue inside the old chimney. The technique works for both gas and wood-burning appliances and has two big advantages: it reinforces deteriorated masonry from the inside, and it leaves a perfectly smooth flue that drafts very well.[8]

Cost is $3,500 to $7,000 for a typical Ontario retrofit. Install requires dry weather for the pour to cure properly, which limits Ontario installs to roughly May through October in most of the province. Cast-in-place is the right answer when the old masonry is structurally compromised but the chimney otherwise has to stay (heritage home, tight side-yard clearances that make exterior rebuild impractical, or a wood-burning fireplace where the original character must be preserved). See Gas Fireplace Cost Ontario 2026 for adjacent fireplace conversion pricing.

Install Cost Ranges (Ontario 2026)

These figures assume a reputable Ontario installer with insurance, warranty, and TSSA or WETT credentials. A handyman quoting half these numbers is not doing the same job.

WETT Inspection Process

WETT (Wood Energy Technology Transfer) is the Canadian credentialing body for professionals who evaluate and install solid-fuel-burning systems. A WETT certified inspector has passed a written exam on CSA B365 installation code and is listed in the WETT public directory.[4]

A Level 1 WETT inspection is a visible-components check: the appliance, the connector pipe, the chimney interior from the top (with mirror or camera), and the clearances to combustibles. It takes about an hour and costs $200 to $350. A Level 2 inspection adds a video scan of the entire flue, runs $300 to $500, and is what most insurers actually want when a policy is first written. Level 3 involves partial dismantling and is rare outside of post-fire investigations.

The inspector issues a WETT inspection report that lists deficiencies (improper clearances, failed liner, missing spark arrestor, wrong connector material) and a pass or fail verdict. Insurance companies use this report directly. A fail usually means you either fix the deficiencies and re-inspect, or stop using the wood appliance and convert to something else (gas insert, electric, or decommission entirely).

Ontario Fire Code and CSA B149.1 Rules

Three documents govern chimney work in Ontario and they work together.

The Ontario Fire Code, O. Reg. 213/07 under the Fire Protection and Prevention Act, requires chimneys and flues serving fuel-burning appliances to be maintained in safe operating condition, accessible for inspection, and free of combustible accumulations.[5] This is the general maintenance obligation that lands on every Ontario homeowner who owns a chimney.

CSA B149.1 is the national installation code for natural gas and propane appliances, adopted into Ontario regulation and enforced by the TSSA.[1][2] It specifies venting sizing tables, material requirements, clearances, and installation practices for gas appliances. When a B149.1 compliant install requires a liner, the liner itself must meet the listed standards for the appliance category and temperature class. Gas work, including liner installation for a gas appliance, must be performed by a TSSA licensed gas fitter (G2 or G1).

CSA B365 is the corresponding code for solid-fuel appliances (wood stoves, wood inserts, pellet stoves, wood-burning fireplaces). It governs liner type, clearances, connectors, and installation practices for wood systems.[3] WETT certified professionals are the population trained against B365 specifically.

The Ontario Building Code (O. Reg. 332/12) sets the minimum standards for chimney construction in new builds and major renovations, including masonry chimney wall thickness, flashing, and clearance to combustibles.[6] For a retrofit liner job in an existing home, B149.1 or B365 is the document that matters most. OBC becomes relevant when the chimney itself is rebuilt or when a major renovation triggers a building permit.

What this means in practice: a retrofit stainless steel liner install for a gas water heater in Ontario involves a TSSA licensed gas fitter, an installation that complies with CSA B149.1 venting sizing, and (depending on the municipality) a gas permit. Homeowner insurance expects the same. If the installer cannot produce a TSSA contractor licence and a written invoice showing B149.1 compliance, the work is not legal in Ontario.

Frequently Asked Questions

Related Guides

• HVAC Replacement Cost Ontario
• Water Heater Cost Ontario
• Gas Fireplace Cost Ontario 2026