Many older Joliet homes have a single chimney stack carrying two or more separate flues, and frequently at least one is abandoned. An improperly capped abandoned flue can allow combustion gases to migrate between passages, which is a carbon monoxide risk that sweeping alone does not address.
Why one stack often has several flues
In older construction it was normal to run several flues up a single masonry stack: one for the fireplace, one for the furnace or boiler, sometimes one for a second fireplace or a long-removed appliance. Joliet’s substantial stock of pre-1940 homes and converted multi-family properties makes this common here.
Over decades, appliances get replaced, heating systems get converted, and flues fall out of use. What frequently does not happen is proper decommissioning. The flue is simply left, or capped in a way that was never intended to be permanent.
The actual hazard
Flues in a shared stack are separated only by their liners and the masonry between them. When liners deteriorate, which they do over sixty to a hundred years, gaps open between adjacent passages.
The result is that exhaust from an active appliance can cross into a disused flue and, from there, into the building. Carbon monoxide is colourless and odourless, and this failure mode produces no smoke and no smell in the room. It is genuinely one of the more dangerous things we find, and it is invisible without a camera.
Sweeping does not detect it, because sweeping cleans a flue rather than evaluating the masonry between flues.
How it gets diagnosed properly
Each flue in the stack has to be scanned individually. A Level 2 inspection runs a camera the full length of every passage, and we record the footage so you can see the condition yourself.
If we find breaches, the remedy is usually stainless relining of the active flue, which restores a continuous sealed path regardless of what the surrounding masonry is doing, plus proper permanent capping of any genuinely disused flue.
If you own a multi-family or converted property in Joliet, this is worth doing once even if nothing seems wrong. Written reports are suitable for landlord and association records.
Talk to a local chimney pro
We cover Joliet as the southern edge of our route, with no trip charge, seven days a week.
Written by Josh Amber, co-owner of Ember Chimney Sweepers, Oswego IL. Published September 28, 2026.