Category: Chimneys & Fireplaces

An older house in Menasha, gas furnace put in sometime in the nineties, original clay-tile chimney from 1924. The homeowner called me because chunks of orange clay were showing up in the cleanout door. He thought a bird had gotten in.

What he had was thirty years of a modern high-efficiency appliance venting into a flue that was built for coal smoke, and the tile had been coming apart from the inside the whole time.

Why old flues fail on new equipment

A coal or wood fire sends up hot, dry gas. The flue stays well above the temperature where anything condenses, and the clay liner lasts the better part of a century.

Modern gas equipment sends up gas that’s much cooler and full of water vapor. In an oversized masonry flue in a Wisconsin winter, that gas cools before it gets out, and water condenses on the tile — mildly acidic water, running down the inside of the chimney, all season, every season.

That condensate attacks the mortar between the tiles first. Then it gets behind them into the brick. In a climate that freezes and thaws as hard as ours, water sitting in that masonry does the rest. By the time clay shows up in the cleanout, the liner has been failing for years.

What an unlined or failed chimney actually risks

Two things, and they’re different in kind.

With gas appliances the risk is carbon monoxide finding its way through gaps in a deteriorated liner into the house, usually through an adjacent chase or an old fireplace opening. This is the one that matters and it’s silent.

With any solid fuel — a wood stove tied into an old flue, which we still see plenty of around here — the risk is a chimney fire finding an unlined path to framing. That’s why the codes want a continuous liner and clearance to combustibles, and it’s why insurers ask about it.

What relining involves

For gas, a properly sized aluminum or stainless liner dropped down the existing flue, top plate, and connection at the appliance. Sizing matters more than people expect — putting a liner that’s too large in the flue recreates the same condensation problem you’re trying to solve.

For wood, stainless only, usually insulated, and the insulation isn’t optional in an exterior chimney in this climate. An uninsulated stainless liner on a north wall will still run cold enough to condense creosote.

The other path is a cast-in-place liner, where a cement-based mix is poured around a form to build a new smooth flue inside the old one. It’s more disruptive and more expensive, but on a chimney with structural gaps it does two jobs at once.

Whether relining is even the right call depends on the condition of the stack above the roof, which is a separate question I’ve worked through in line it or take it down and rebuild.

Costs and what to check first

A stainless liner for a gas appliance in a straight flue runs $2,200 to $4,500 installed. Insulated stainless for a wood stove is $3,000 to $6,500. Cast-in-place is $6,000 to $12,000. Add a crown rebuild at $600 to $1,800 if the top is cracked, which it usually is on a hundred-year-old chimney.

Before any of that, get a camera inspection — $150 to $400, and it’s the only way anyone can honestly tell you what’s happening inside. A contractor who quotes a reline without running a camera is quoting a guess. The Department of Energy’s material on home heating systems is a reasonable plain-language starting point on how venting fits with the appliance you have.

One more thing worth doing every fall: a carbon monoxide detector on each floor, tested. It costs thirty dollars and it covers you while you decide about the chimney.

Frequently asked questions

Does a gas furnace need a chimney liner? Usually yes when it vents into an old masonry chimney. Modern furnaces produce cooler, wetter exhaust that condenses in an oversized flue, and the acidic condensate breaks down the clay tile and mortar over time.

How do I know if my chimney liner has failed? Pieces of clay tile in the cleanout, staining or damp patches on the chimney breast inside the house, and a strong draft smell are all signs. A camera inspection at $150 to $400 is the only way to confirm it.

How much does relining a chimney cost? A stainless liner for a gas appliance is $2,200 to $4,500. Insulated stainless for a wood stove runs $3,000 to $6,500. Cast-in-place relining is $6,000 to $12,000 and also addresses structural gaps.

A couple in the Catalina Foothills had me build a kiva-style corner fireplace on a covered patio. Beautiful spot, view down the valley, and they wanted to use it on winter evenings. First cold night they lit it, the patio filled with smoke, and they called me sounding like they’d bought a very expensive sculpture.

Nothing was wrong with the masonry. The problem was that a covered patio with a low ceiling and a nine-foot wall on the windward side had no way to feed air to the fire. We cut a vent, and it drew fine after that. But it’s a good illustration of the thing people underestimate — an outdoor fireplace is an air problem before it’s a masonry problem.

Kiva versus box, and what you’re choosing

The traditional kiva shape — the rounded adobe corner fireplace you see all over the Southwest — is small, shallow, and built to throw heat into a room by radiation rather than to burn a lot of fuel. The opening is modest, often under two feet wide. That’s not a limitation; it’s why it drafts well in a corner with a short flue.

A rectangular firebox with a wide opening is a different machine. It burns bigger logs, produces more heat, and it needs proportionally more flue and more air. Where people get into trouble is wanting the kiva look with a box-sized opening. Widen a kiva mouth past about thirty inches and the same flue that used to draw will start spilling smoke.

Whatever the shape, what matters is the ratio of fireplace opening to flue area. The old working number is about a tenth, more if the chimney is short. A mason who builds these regularly sizes it without drama; a general contractor building his first one usually undersizes the flue, and there’s no fixing that afterward except by making the opening smaller.

Height and what’s around it

Two more geometry rules earn their keep outdoors. The flue should terminate at least two feet above anything within ten feet of it, and three feet above where it passes the roof or patio cover. Under a deep patio roof that means the chimney punches through and keeps going, which surprises people who pictured it stopping at the ceiling.

And it needs air from somewhere. On an open patio the air is free. On a covered, walled outdoor room — which is most of what gets built here now — I plan a low intake on the windward side or leave a gap that isn’t going to get closed in later with a screen enclosure.

Materials that survive the swing

The firebox takes firebrick and a refractory mortar, not standard brick and Portland. That’s not a preference, it’s the difference between a firebox that lasts thirty years and one that spalls apart in four. Behind and around it, block or adobe is fine.

Outside, the desert does something a mild climate doesn’t: it heats one face to a hundred and thirty and drops it forty degrees overnight, all year. Anything rigid and applied cracks eventually. I detail a cap with a drip edge, an expansion allowance where the chimney meets a wall, and no film-forming coating on the stack.

If you’re weighing this against a fire pit or a simpler feature, the tradeoffs run deeper than cost, and I’ve laid them out in planning a backyard fire feature in masonry.

Wood, smoke, and the neighbors

Worth knowing before you build: burning conditions get restricted in this region on poor air quality days, particularly in winter when inversions trap smoke in the valley. Wood-burning is generally fine but not unconditionally, and it’s the kind of thing that decides whether a fireplace gets used twice a year or twenty times. The EPA’s Burn Wise program covers what actually reduces smoke — dry seasoned wood, hot fires, and not smoldering — and it makes a real difference to whether your patio is pleasant.

Plenty of clients end up on gas for that reason — the look without the argument, at the cost of the smell and the sound they wanted in the first place.

What it costs

A modest kiva-style corner fireplace, built in place with firebrick and finished in plaster, runs about $6,500 to $12,000 here. A larger rectangular firebox with a stone or adobe face and a taller stack is $14,000 to $30,000, and the stack height is usually what moves the number, not the firebox.

Gas plumbing adds $1,200 to $3,500 depending on the run. Cutting a proper air intake on an enclosed patio afterward, as we did in the Foothills, was about $900 — cheap, but it should have been in the drawing.

Frequently asked questions

Why does my outdoor fireplace smoke? Usually an undersized flue for the opening, a chimney that doesn’t terminate high enough above nearby walls or roof, or no makeup air on an enclosed patio. The first two are geometry and expensive to correct; the third is often a vent that costs under $1,000.

Can a kiva fireplace be built with regular brick? The outer structure can be adobe, block or brick, but the firebox itself needs firebrick set in refractory mortar. Standard brick and Portland mortar break down quickly under direct fire.

How tall does an outdoor chimney need to be? At least three feet above where it passes the roof or patio cover, and two feet above anything within ten feet horizontally. Under a deep patio cover that usually means the stack continues up through the roof rather than stopping at the ceiling.

Nobody rebuilds a whole chimney because a whole chimney failed. They rebuild because one section failed and nobody looked closely enough to say which. A chimney is really three structures stacked on each other, each with its own weather, its own loads, and its own failure mode, and the section that has gone bad is what sets the price of the repair.

A chimney fails in sections, and the section sets the price

At the bottom sits the firebox and the smoke chamber, sheltered inside the house and exposed to the highest temperatures. In the middle is the run through the building, usually the most protected part and the one that most often survives. Above the roofline is the stack, which gets the wind, the rain, the freeze-thaw cycling and the sun, all with masonry that has water coming at it from three sides. Repairs to those three zones are not the same job and should never be quoted as one number.

Above the roofline is where most of the damage lives

If a mason is quoting a rebuild, it is usually a rebuild of the stack. The crown is the first thing to go: a thin skim of mortar troweled on decades ago cracks, water runs straight into the top of the masonry, and every winter after that widens the path. Then joints wash out, the units start to shift, and the top few courses lean. Rebuilding from the roofline up is a well-defined, contained job. It is also the one that is easy to defer until the chimney is genuinely unsafe.

What a liner can and cannot rescue

Relining fixes the flue, and the flue is the passage the exhaust travels through. A stainless liner is the standard answer for a cracked clay tile flue, an oversized flue serving a modern appliance, or a chimney being converted to gas. What relining does not do is repair the masonry around it. If the joints are open, if the stack is leaning, if water is entering through the crown, a liner is a new pipe inside a wall that is still coming apart. The liner will work. The chimney will keep deteriorating around it.

When rebuilding is the cheaper answer

Tear-down becomes the economical choice when the structure has lost its geometry. A stack that is out of plumb, units that can be moved by hand, mortar you can rake out with a key, a crack that runs through the full thickness, or a chimney that has separated from the house: those are not liner problems. There is also a decision people avoid, which is whether an unused chimney is worth keeping at all. If nothing vents through it, taking it down below the roofline and detailing the roof properly ends the maintenance permanently for less than a rebuild.

Get a camera in it before anyone quotes

An internal video inspection is the difference between a diagnosis and a guess, and it costs a small fraction of any repair it might rule out. It shows the condition of the flue tiles, the smoke chamber, and any breach between the flue and the surrounding structure. Combine it with a look at the crown and the joints from a ladder or a drone, and the scope of work becomes an argument about facts rather than opinions. Quotes written without one tend to price the worst case, because the contractor is carrying the uncertainty.

Frequently asked questions

How long does a clay flue liner last? Decades under normal use, but a single flue fire or repeated water intrusion can crack tiles well before that. Cracked tiles let combustion gases reach the surrounding masonry and the framing, which is why a cracked liner is treated as a safety issue rather than a maintenance item.

Can only the top of a chimney be rebuilt? Yes, and it is the most common repair there is. A rebuild from the roofline up with a properly formed and overhanging crown addresses the majority of chimney deterioration, because that is where nearly all of the water gets in.

Is a leaning chimney always an emergency? Not always, but it always needs looking at quickly. Some lean has been present since construction and has not moved in decades; movement that is recent, or a gap opening between the chimney and the wall, means the footing or the structure is failing and the area below it should be treated as unsafe until someone qualified has seen it.

Almost every fire feature conversation starts with a picture the client saved, and almost every one of them ends somewhere different once we walk the yard. The decision is not really fire pit versus fireplace. It is what the prevailing wind does, where people already sit, and how much structure the ground can carry.

Wind and sightlines decide this, not the catalogue

A fire pit is social in the round: everyone faces in, nobody is behind anyone, and it works in an open yard. A fireplace is directional. It gives you a wall, a mantel, shelter from wind coming off one side, and a room-like feel on a patio that otherwise has no edges. On a valley lot where the evening breeze runs the same direction most nights, a fireplace placed to block it turns a patio from occasionally usable into usable most of the year. In a flat, open yard with no dominant wind, the same money buys a lot more seating as a pit.

What sits underneath matters more than the facing

A fireplace is a masonry structure with real weight, often several tons once you count the chimney. It needs its own footing, sized and set below the frost line, and it needs that footing poured on undisturbed soil rather than on backfill or a patio base. Tying it to a slab that was designed to carry patio furniture is how a good-looking fireplace ends up with a stair-step crack through the firebox in its third winter. A fire pit is far more forgiving, but it still wants a compacted base and drainage so the bowl does not hold standing water.

Firebrick is not a line item to trim

Anything the flame touches has to be firebrick laid in refractory mortar. Ordinary brick and standard mortar are not formulated for that temperature cycling, and they spall and crumble quickly once they start. The outer shell can be whatever matches the house, whether brick, stone veneer, or block with a facing, but the firebox and the throat are not the place to economize. The same applies to the flue: an undersized or badly proportioned throat produces a fireplace that smokes into the seating area every time you use it, and that is expensive to correct after the fact.

Fuel, clearances, and what the local rules cover

Gas gives you instant on and off, no smoke, and no wood storage, at the cost of a gas line and a permit for it. Wood costs less to build and more to live with. Either way, distance rules apply: separation from the house, from property lines, from overhanging limbs, and from anything combustible in the seating area. Jurisdictions differ, and open burning is sometimes restricted outright during dry stretches, so the clearances are worth checking before the footing is laid, not after.

Where the budget actually goes

A simple, well-built pit on a proper base is a modest project. A full masonry fireplace with a footing, firebox, flue, hearth, and a veneer that matches an older house is a different order of magnitude, and most of the increase is invisible: excavation, concrete, and the firebox assembly. Seat walls, a hearth extension, and lighting are usually where the number moves after the fact, so they belong in the first conversation.

Frequently asked questions

Do I need a permit for a backyard fireplace? Usually yes for a permanent masonry fireplace, and generally yes for any gas line, while a portable pit typically needs none. Because the rules and setbacks are local, the time to confirm is before excavation.

How far from the house should it sit? Far enough to satisfy the local clearance requirement and to keep smoke out of windows and doors, which is often further than the minimum. Wind direction on summer evenings matters as much as the number in the code.

Can ordinary brick be used in a fire pit? Not on any surface that meets flame. Those faces need firebrick set in refractory mortar, which tolerates heat that cracks common brick and standard mortar. Regular units are fine for the outer structure only. That detail travels: a Staten Island masonry contractor building an outdoor fireplace specifies the same firebrick and refractory mortar we do.