How these chimneys came to be
The Massachusetts Historical Commission’s survey of New Bedford describes two-family houses through the 1880s and then, from the 1890s, large districts of three-deckers along Cove Street in the South End and Acushnet Avenue in the North End, with Clark’s Point building three-deckers on Brock Avenue and two-families behind. Those buildings were heated floor by floor with coal or wood stoves, and each stove needed a flue.
That is why so many of the city’s multifamily chimneys are tall, slim brick stacks with several flues side by side, rising well above a three-story roof. Most were built before clay flue liners were routine, so some flues are bare brick inside and others had liners added later.
What the flues do now
Almost no three-decker still burns coal on every floor. Most switched to central heat, then often to gas, and many now have separate boilers or furnaces and water heaters for each unit. Old stove flues were reused, closed or simply left. It is common to find one flue venting a gas boiler, another a water heater, and the rest unused or abandoned in ways nobody recorded.
Reuse is where trouble starts. A tall masonry flue built for hot coal smoke is often too large and too cold for a modern gas appliance. The cooler, wetter exhaust can condense on the way up, and the condensate attacks mortar and brick from inside. Staining, crumbling mortar at the base, tile fragments in the cleanout and water at the connector are the typical signs.
Problems that come up again and again
- Weathered tops: the exposed section above a three-story roof takes the most wind, rain and salt, so loose top courses and cracked crowns are common.
- Open flues: flues without caps let in rain and give birds a nesting site, and one ordinary cap rarely covers a multi-flue stack.
- Condensation damage: oversized flues venting gas appliances can damage the masonry from inside.
- Unknown history: owners often don’t know which flue serves which unit, or whether unused flues are properly closed.
- Access: reaching the top safely on a three-story roof takes the right equipment and care.
Who is responsible
Where one owner rents out the units, the owner is responsible for the chimney, including flues serving tenants’ appliances. Tenants who notice smoke, odors, stains or debris should tell the owner or manager rather than booking work themselves.
In buildings converted to condominiums, the chimney is usually a common element under the condominium documents, and the association arranges and pays for exterior work. Read the master deed and bylaws before booking anything.
A simple routine for owners
- Write down which flue serves which unit, appliance or fireplace, and which flues are unused.
- Have every flue inspected once a year, as NFPA 211 recommends for chimneys and vents, not just any working fireplace.
- Make sure every flue in use has a cap, and that unused flues are properly closed at the top.
- Ask for a camera inspection of a flue before a new boiler or water heater is connected to it.
- Keep findings and photographs with the building records for the next owner or board.
When an appliance is replaced
The best moment to think about the chimney is when a boiler, furnace or water heater is replaced. A new high-efficiency appliance may vent through the wall and not use the chimney at all, leaving a flue unused or serving only one smaller appliance. Or it may use the chimney but need a liner sized for it.
Either way, the appliance’s venting instructions and the local code decide what the flue needs. NFPA 211 calls for a Level 2 inspection, including a video scan, when the appliance, fuel or liner changes, which gives the installer and the chimney contractor a shared picture before connection day.
Unused flues in a working stack
Most three-deckers have at least one flue that no longer serves anything. How it was left matters. A flue that is open at the top takes in rain, which soaks the masonry around the working flues beside it. A flue open at the bottom, behind an old stove thimble or a boarded-up fireplace, lets warm, moist air from the apartment drift into a cold flue, where it condenses and wets the brick from inside.
Unused flues are best closed deliberately: a cover at the top that keeps out rain and animals, and a proper closure at the bottom where the flue opens into a unit. Before anything is closed, make sure nothing is still connected to it; in older buildings, a forgotten water heater on a supposedly abandoned flue is not unusual.
Carbon monoxide alarms
Massachusetts requires carbon monoxide alarms in residences with fossil-fuel-burning equipment or enclosed parking. In a multifamily building, every unit needs working alarms. A blocked or damaged heating flue can push exhaust back into a unit, and the alarm is the warning. Test them, and replace them on the manufacturer’s schedule.
Sources we checked
- Massachusetts Historical Commission: Reconnaissance Survey Town Report, New Bedford
- City of New Bedford: Department of Inspectional Services (budget and service description)
- NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances
- Chimney Safety Institute of America: The Three Levels of Chimney Inspections
- Mass.gov: Massachusetts law about carbon monoxide detectors
General information for homeowners from Chimney Champ’s New Bedford. It cannot stand in for an inspection of your own chimney, and questions about code are decided by your local building or fire official.