Chimney rebuild and lining.

What the chimney does now

A 1920s River Forest chimney usually holds two or three flues: one for the coal furnace in the basement, one for the fireplace, sometimes one for a kitchen stove. The coal furnace became a gas furnace in the 1950s, sharing its flue with a gas water heater. The kitchen flue was capped. The fireplace flue may or may not have been used since the Bulldogs last won a conference title.

Each of those changes asked the masonry to do something it was not designed for, and the chimney has been quietly deteriorating from all three ever since. Which is why the estimate on your counter probably arrived right after another contractor mentioned the word "liner."

How chimneys fail

From the top down. The crown, the concrete or mortar slab that seals the top of the masonry, cracks and lets water into the brick below. Without a cap, rain falls straight down the flue. Water in the top courses freezes, and the brick spalls and the mortar joints fail. Eventually the top few feet lean, and the flashing where the chimney meets the roof opens up and the leak shows up in the bedroom ceiling.

Inside, flue gases carrying water vapor and acids condense on the clay tile liner and eat the mortar between the tiles. Tiles crack, shift and fall. That damage is invisible from the ground and is exactly what a camera inspection is for.

Look up from the sidewalk before you read any estimate. A crown you can see daylight through and white staining down the brick tell you most of what you need to know.

The furnace connection

The most common trigger for chimney work here is a furnace replacement. An 80% furnace vents hot exhaust up the chimney and keeps the flue warm and dry. A new 96% condensing furnace vents out the side wall through plastic pipe, and the chimney flue it shared is left to the water heater alone.

A water heater's exhaust is small and cool. In a flue sized for two appliances it rises slowly, condenses on the way up, and the acidic condensate runs down the clay tile and eats the mortar joints. Within a few years the liner is failing and, in the worst case, exhaust is leaking into the house. The HVAC guide covers this from the furnace side; the fix from the chimney side is a properly sized liner.

A furnace estimate that does not mention the water heater flue is missing a line. A chimney contractor who asks what furnace you have is doing the job right.

Liners, in plain terms

A liner is a pipe inside the flue that carries the exhaust and protects the masonry. Three kinds turn up on estimates. Clay tile is what your chimney has now; it is repaired by replacing broken tiles, which is rarely practical. Stainless steel, rigid or flexible, is the standard fix: sized to the appliance, insulated, dropped down the flue and connected at the bottom. Cast-in-place liners pour a cement mix around a form inside the flue and also stabilize the masonry; they are used for fireplace flues and deteriorated stacks.

Sizing is the whole trick. A liner for a water heater alone is small, around three or four inches. A liner for a fireplace is large. The estimate should name the appliance the liner serves, the diameter, the material grade, and whether it is insulated. An insulated liner keeps the exhaust warm and stops the condensation that started the problem.

Reading the estimate, row by row

Line these rows up across every estimate you collect. Where two of them differ, that is where the price difference usually lives.

Scope. Which of the top-down items, and how many courses.

Liner type and size. Appliance served, diameter, material grade, insulated or not.

Crown and cap. A poured concrete crown with a drip edge lasts decades. A mortar wash, mortar troweled over the top course, is the old way and cracks within a couple of winters.

Brick and mortar. Same rules as the walls: matched salvage brick and a lime-rich mortar. The tuckpointing guide explains why.

Crown, cap and the top courses

The crown should be concrete, two inches thick at the edge, overhanging the brick with a drip edge so water falls clear of the face, with a bond break around the flue tiles so they can expand. A cap over each flue keeps rain, leaves and raccoons out; a full-coverage stainless cap over the whole crown protects the crown itself.

If the top courses are spalled, loose or leaning, they come down and get relaid. Typically three to ten courses. Below that line the brick has usually stayed dry enough to keep.

Rebuild from the roofline

When the damage runs past the top courses, the standard repair is to take the chimney down to the roofline and rebuild it: new brick or salvaged, new flue tile or a liner, new crown, cap and flashing. It is a two-to-four-day job with scaffolding and it is what most "chimney rebuild" estimates in River Forest actually describe.

A rebuild below the roofline, into the attic or down to the ground, is rare and expensive and usually means the chimney has structural problems, not weather problems. Get a second mason's eyes on it.

Flashing

Where the chimney passes through the roof, sheet metal step flashing woven into the shingles and counter flashing let into the mortar joints above it keep water out. It is the most common source of a chimney leak, and the cheapest to fix, and it gets caulked instead of replaced by contractors who do not want to cut into the brick.

New flashing means cutting a reglet into the mortar joint, setting the counter flashing into it, and sealing with mortar or a proper sealant. Caulk smeared along the joint is a one-season patch. If the estimate says "seal flashing," ask what that means.

Fireplaces

If you burn wood, the fireplace flue needs its own Level 2 inspection: a camera run down the flue looking for cracked tiles, missing mortar, and creosote. A cracked tile liner on a wood-burning flue is a fire hazard, not a maintenance item, and the fix is a stainless or cast-in-place liner sized to the firebox. Damper repair and a top-sealing damper are small adds that pay back in heating bills.

If you do not burn wood and never will, capping the fireplace flue and having the damper sealed is a reasonable way to stop paying to heat the sky.

What drives the price

Scope, by an order of magnitude: crown and cap in the low four figures, liner in the mid four figures, rebuild from the roofline in the high four to low five figures. Then height and roof pitch, which set the staging. Then the liner grade and insulation. Then brick matching and lime mortar, which add hundreds and are worth it.

Red flags

• A liner quoted with no diameter and no appliance named.
• A mortar-wash crown.
• "Seal flashing" instead of replace.
• Type N mortar on a 1920s stack.
• No camera inspection before a rebuild recommendation.
• No permit line. Chimneys and flues are both on the Village list.

Questions to ask

• What did the camera show, and can I see the video?
• Which appliance is the liner for, what diameter, and is it insulated?
• Is the crown poured concrete with a drip edge?
• Are you replacing the flashing or sealing it?
• What mortar, and where does the brick come from?
• How many courses come down, and how did you decide?

The short list

Camera first. Liner sized to the appliance and insulated. Poured crown with a drip edge. Flashing replaced, not sealed. Lime mortar and matched brick. Permit included. Six items, and the chimney that has been quietly failing since the Eisenhower administration gets another fifty years.

Permits, programs and the Village