Chimney Repair, Cleaning & Relining
Core Mechanical Group repairs, relines, sweeps and inspects chimneys, including the masonry flues that vent gas boilers and water heaters in pre-war row houses. We handle stainless liner installation, crown and cap repair, repointing, draft testing, and NFPA 211 Level 1 and Level 2 inspections.
- Water heater or boiler backdrafting
- Carbon monoxide alarm near the boiler
- White staining and crumbling mortar
- Water leaking down an interior wall
- Cracked crown or missing chimney cap
- Spalled brick and open joints
- Unlined or cracked clay tile flue
- Creosote buildup in a fireplace flue
- Smoke pushing back into the room
- Animal or debris blockage
- Chimney inspection for a sale or violation
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Article reviewed and technically verified by Victor Orlov, Core Mechanical Group LLC.
What These Chimneys Are Built Like
Most of the chimneys we work on sit inside brick row houses and brownstones built between 1880 and 1930. They were built as multi-flue masonry stacks for coal, then converted to oil, then to gas. Each conversion left the flue oversized for the appliance now attached to it.
Two structural details drive most of the repairs we quote. The party-wall chimney is shared with the neighbouring building and only the top few feet are exposed, so freeze and thaw cycles concentrate damage at the crown and the top three or four courses of brick. The second is the unlined flue: buildings from that era were commonly built with brick-on-brick flues and no clay tile at all, or with clay tile that has since cracked at the joints.
Neither condition shows up from the street. Both show up on a camera scan, which is why we run one before quoting relining work rather than after.
Chimney Liner Installation and Relining
This is the work that connects most directly to the rest of what we do. When a homeowner replaces an old atmospheric boiler with a high-efficiency condensing unit, the new boiler vents through a PVC pipe out the side wall. The gas water heater that used to share the chimney is left connected to it alone. The industry term for that water heater is orphaned.
A flue sized for a boiler and a water heater together is far too large for the water heater by itself. The exhaust from one 40-gallon tank cannot warm that much masonry, so it never establishes draft. Water vapour in the exhaust condenses on the flue walls instead of leaving the building.
Two things follow. The condensate soaks into the brick and mortar, which produces the white efflorescence staining and the crumbling joints homeowners notice on the interior chimney breast. And when draft fails completely, combustion gases containing carbon monoxide spill out of the draft hood at the top of the water heater into the basement.
How We Size and Fit the Liner
The fix is to resize the flue rather than the appliance. We install a stainless steel liner sized to the water heater's input rating and the vent height, insulate it where the code and the manufacturer's listing require it, and rebuild the vent connector from the draft hood to the thimble at the correct rise and pitch.
Then we run a draft test at the draft hood with the appliance firing and every exhaust fan in the building switched on, because that is the condition under which spillage actually happens.
We do the same relining work after an oil-to-gas conversion, after a chimney fire, and whenever a camera scan shows cracked or missing clay tile. If your boiler or water heater is being replaced, ask about the flue before the old unit comes out. Relining costs less when the connector is already open.
The appliances we most often find on these flues are cast-iron boilers from Weil-McLain, Burnham and Slant/Fin, and atmospheric tank water heaters from A.O. Smith and Bradford White. The full list of equipment we service is on our brands page.
Relining is not the only answer. If the water heater is also due for replacement, a sidewall-vented tankless unit from Navien, Rinnai or Noritz takes the appliance off the chimney entirely, and the flue can then be capped. Households moving to a ductless heat pump for heating end up in the same place. We will tell you which of the two costs less over ten years before you decide.
Symptoms, Likely Causes and What We Check First
| What you notice | Most likely cause | What a technician checks first |
|---|---|---|
| CO alarm near the boiler or water heater | Draft failure on an oversized or blocked flue | Draft test at the draft hood under worst-case depressurisation, then a camera scan for blockage |
| White chalky staining on the chimney breast | Flue gas condensate soaking through unlined masonry | Flue size against appliance input, liner condition, moisture reading on the interior face |
| Water dripping down an interior wall after rain | Failed crown, missing cap, or flashing separation at the roof line | Crown for cracks, cap and screen, counter-flashing and the top courses of brick |
| Brick faces flaking off near the top | Freeze and thaw spalling, usually with saturated mortar joints | Mortar hardness, joint depth, and whether the crown is shedding water away from the brick |
| Smoke pushing back into the room | Blockage, closed or broken damper, or negative pressure in the house | Damper travel, smoke test, and pressure difference with the exhaust fans running |
| Strong smell from the fireplace in summer | Creosote deposits absorbing humidity | Deposit thickness and stage, then whether the flue is drawing the wrong way |
| Chirping, scratching or nesting debris | Animal entry through a missing or damaged cap | Cap and spark screen, then a camera scan for nesting material in the flue |
Chimney Sweeping and Creosote Removal
The Chimney Safety Institute of America sets the practical threshold for a wood-burning fireplace flue at one eighth of an inch of sooty buildup, and calls for the flue to be swept at that point. It also carries the NFPA 211 requirement that chimneys, fireplaces and vents be inspected at least once a year for soundness, freedom from deposits and correct clearances. Both are on the CSIA homeowner resources page.
We sweep with rotary rods and a sealed negative-air vacuum at the fireplace opening, so the soot leaves through the hose rather than into the room. Glazed creosote, the hard shiny stage, does not come off with a brush and needs either a rotary chain head or a chemical treatment followed by a second visit. We tell you which stage you have before we start, because the two jobs cost differently.
Gas appliance flues do not build creosote, so they are cleaned rather than swept. Scale, rust flakes and mortar debris get vacuumed out of the base of the flue and out of the vent connector, which is where blockages usually collect.
Crown, Cap, Flashing and Repointing
The crown is the sloped concrete or mortar wash on top of the stack. Its job is to throw water clear of the brick below. On an older row house the crown is usually the original mortar wash, it has cracked through, and every rainfall is running straight into the top of the masonry. That is the single most common source of the leak that shows up on a top-floor ceiling.
We rebuild crowns as a proper cast crown with an overhang and a bond break at the flue, fit a stainless cap and spark screen sized to the flue, replace counter-flashing where it has pulled away from the brick, and repoint open joints with a mortar mix matched to the softness of the original.
Matching the mortar matters on soft nineteenth-century brick. A hard modern mix is stronger than the brick around it, so the brick face spalls off instead of the joint wearing. Where the top courses have already lost their faces, the repair is a partial rebuild from the roof line up rather than a patch.
Chimney Inspection and Code Compliance
Inspections follow the three levels defined in NFPA 211. The level is set by the circumstances, not by what a customer asks for. Replacing a boiler or water heater counts as an appliance replacement, which puts it in the Level 2 list. So does a sale.
If you are buying a brownstone with a gas boiler on a masonry flue, the video scan is the part of the inspection that finds cracked tile, and it is the part most general home inspections leave out.
| Level | What it covers | When it applies |
|---|---|---|
| Level 1 | Readily accessible parts of the chimney inside and out, the appliance, and the connection to the chimney. Flashlight and mirror. No camera required. | Annual check on a chimney in continued service, with no changes to the system and no known problem. |
| Level 2 | Everything in Level 1, plus a recorded video scan of the full flue interior and inspection of accessible concealed spaces such as the basement, attic and chases. | Fuel change, an appliance added or replaced, after a chimney fire, after storm or impact damage, on sale or transfer of the property, or when a Level 1 finding needs a closer look. |
| Level 3 | Everything in Level 2, plus removal of building materials to reach concealed parts of the chimney. | Only when a Level 2 scan has documented a specific hidden hazard. It should never be proposed without those findings. |
Code, and one thing worth clearing up
Requirements vary by municipality, so confirm yours before work starts. Inside the five boroughs, gas appliance venting falls under Chapter 5 of the NYC Fuel Gas Code, other appliances under Chapter 8 of the Mechanical Code, and masonry chimney construction under Chapter 21 of the Building Code. The height rule people run into most often is the one for appliances operating below 600 °F: the chimney has to terminate at least three feet above the point where it passes through the roof, and at least two feet above anything within ten feet of it. Adding a rear extension or a bulkhead can put an existing chimney out of compliance without anyone touching the chimney itself.
Local Law 152 is a gas piping inspection, not a chimney inspection, and it applies inside New York City only. It requires gas piping in covered buildings to be inspected at least once every four years by a Licensed Master Plumber, on a staggered schedule by community district, and it exempts one- and two-family homes and other Occupancy Group R-3 buildings. The details are on the NYC Department of Buildings gas piping inspection page. A chimney or flue problem found during that inspection is a separate scope of work.
What a Chimney Service Call Looks Like
Victor Orlov and our technicians work the same sequence on every chimney call, whether it started as a leak or a CO alarm.
- Identify every appliance on the flue and record its input rating from the data plate, along with the vent height and the flue's internal dimensions.
- Run a combustion and draft test at the draft hood with the appliance firing and the building at worst-case depressurisation: bath fans, kitchen hood and dryer all running, windows shut.
- Scan the flue on camera from the base and from the top, recording the position of any crack, offset, blockage or missing tile.
- Inspect the crown, cap, flashing and the top courses of brick from the roof.
- Show you the footage and the readings, then quote the work the findings actually support.
Where relining is the answer, we size the liner from the numbers in step one rather than from the size of the existing flue. That is the difference between a liner that drafts and a liner that repeats the original problem in stainless.
Coverage and Booking
We are open seven days a week from 7am to 10pm. How far we travel depends on the job and on the day, so call us with your address and we will tell you straight away whether we can reach you, or check the current list on our service area page. Chimney relining, crown rebuilds and repointing are scheduled work rather than same-day work, because they depend on dry weather and on the camera scan coming first. Draft failures, CO alarms and blocked flues are treated as urgent and dispatched the same day. Related work we handle on the same visit includes boiler repair and installation, heating system repair, new boiler and furnace installation, and the gas line and plumbing work a flue change sometimes needs. Everything mechanical in the building sits under HVAC repair.
